Subjects -> METEOROLOGY (Total: 113 journals)
 Showing 1 - 36 of 36 Journals sorted alphabetically Acta Meteorologica Sinica       (Followers: 4) Advances in Atmospheric Sciences       (Followers: 45) Advances in Climate Change Research       (Followers: 39) Advances in Meteorology       (Followers: 28) Advances in Statistical Climatology, Meteorology and Oceanography       (Followers: 10) Aeolian Research       (Followers: 6) Agricultural and Forest Meteorology       (Followers: 20) American Journal of Climate Change       (Followers: 34) Atmósfera       (Followers: 3) Atmosphere       (Followers: 29) Atmosphere-Ocean       (Followers: 16) Atmospheric and Oceanic Science Letters       (Followers: 13) Atmospheric Chemistry and Physics (ACP)       (Followers: 48) Atmospheric Chemistry and Physics Discussions (ACPD)       (Followers: 16) Atmospheric Environment       (Followers: 75) Atmospheric Environment : X       (Followers: 3) Atmospheric Research       (Followers: 71) Atmospheric Science Letters       (Followers: 40) Boundary-Layer Meteorology       (Followers: 32) Bulletin of Atmospheric Science and Technology       (Followers: 5) Bulletin of the American Meteorological Society       (Followers: 51) Carbon Balance and Management       (Followers: 5) Ciencia, Ambiente y Clima       (Followers: 3) Climate       (Followers: 6) Climate and Energy       (Followers: 7) Climate Change Economics       (Followers: 33) Climate Change Responses       (Followers: 18) Climate Dynamics       (Followers: 44) Climate of the Past (CP)       (Followers: 5) Climate of the Past Discussions (CPD) Climate Policy       (Followers: 51) Climate Research       (Followers: 6) Climate Resilience and Sustainability       (Followers: 21) Climate Risk Management       (Followers: 7) Climate Services       (Followers: 3) Climatic Change       (Followers: 68) Current Climate Change Reports       (Followers: 10) Developments in Atmospheric Science       (Followers: 31) Dynamics and Statistics of the Climate System       (Followers: 5) Dynamics of Atmospheres and Oceans       (Followers: 19) Earth Perspectives - 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Similar Journals
 Monthly Notices of the Royal Astronomical SocietyJournal Prestige (SJR): 2.346 Citation Impact (citeScore): 4Number of Followers: 16      Hybrid journal (It can contain Open Access articles) ISSN (Print) 0035-8711 - ISSN (Online) 1365-2966 Published by Oxford University Press  [415 journals]
• The formation of M101-alike galaxies in the cold dark matter model

Authors: Zhang D; Luo Y, Kang X, et al.
Pages: 1555 - 1562
Abstract: ABSTRACTThe population of satellite galaxies in a host galaxy is a combination of the cumulative accretion of subhaloes and their associated star formation efficiencies; therefore, the luminosity distribution of satellites provides valuable information of both dark matter properties and star formation physics. Recently, the luminosity function of satellites in nearby Milky Way-mass galaxies has been well measured to satellites as faint as Leo I with MV ∼ −8. In addition to the finding of the diversity in the satellite luminosity functions, it has been noticed that there is a big gap among the magnitude of satellites in some host galaxies, such as M101, where the gap is around 5 in magnitude, noticeably larger than the prediction from the halo abundance matching method. The reason of this gap is still unknown. In this paper, we use a semi-analytical model of galaxy formation, combined with high-resolution N-body simulation, to investigate the probability and origin of such big gap in M101-alike galaxies. We found that, although M101 analogues are very rare with probability of $\sim 0.1\ \mathrm{ to}\ 0.2\,{{\rm per\, cent}}$ in the local universe, their formation is a natural outcome of the cold dark matter model. The gap in magnitude is mainly due to the mass of the accreted subhaloes, not from the stochastic star formation in them. We also found that the gap is correlated with the total satellite mass and host halo mass. By tracing the formation history of M101-type galaxies, we find that they were likely formed after z ∼ 1 due to the newly accreted bright satellites. The gap is not in a stable state, and it will disappear in 7 Gyr due to mergers of bright satellites with the central galaxy.
PubDate: Wed, 15 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2621
Issue No: Vol. 508, No. 2 (2021)

• Predictions for anisotropic X-ray signatures in the circumgalactic medium:
imprints of supermassive black hole driven outflows

Authors: Truong N; Pillepich A, Nelson D, et al.
Pages: 1563 - 1581
Abstract: ABSTRACTThe circumgalactic medium (CGM) encodes signatures of the galaxy-formation process, including the interaction of galactic outflows driven by stellar and supermassive black hole (SMBH) feedback with the gaseous halo. Moving beyond spherically symmetric radial profiles, we study the angular dependence of CGM properties around z = 0 massive galaxies in the IllustrisTNG simulations. We characterize the angular signal of density, temperature, and metallicity of the CGM as a function of galaxy stellar mass, halo mass, distance, and SMBH mass, via stacking. TNG predicts that the CGM is anisotropic in its thermodynamical properties and chemical content over a large mass range, $M_*\sim 10^{10-11.5}\, \mathrm{M}_\odot$. Along the minor axis directions, gas density is diluted, whereas temperature and metallicity are enhanced. These feedback-induced anisotropies in the CGM have a magnitude of 0.1−0.3 dex, extend out to the halo virial radius, and peak at Milky Way-like masses, $M_*\sim 10^{10.8}\, \mathrm{M}_\odot$. In TNG, this mass scale corresponds to the onset of efficient SMBH feedback and the production of strong outflows. By comparing the anisotropic signals predicted by TNG versus other simulations – Illustris and EAGLE – we find that each simulation produces distinct signatures and mass dependencies, implying that this phenomenon is sensitive to the underlying physical models. Finally, we explore X-ray emission as an observable of this CGM anisotropy, finding that future X-ray observations, including the eROSITA all-sky survey, will be able to detect and characterize this signal, particularly in terms of an angular modulation of the X-ray hardness.
PubDate: Fri, 17 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2638
Issue No: Vol. 508, No. 2 (2021)

• The diffuse ionized gas (DIG) in star-forming galaxies: the influence of
aperture effects on local H ii regions

Authors: Mannucci F; Belfiore F, Curti M, et al.
Pages: 1582 - 1589
Abstract: ABSTRACTThe diffuse ionized gas (DIG) contributes to the nebular emission of galaxies, resulting in emission line flux ratios that can be significantly different from those produced by H ii regions. Comparing the emission of [SII]λ6717,31 between pointed observations of H ii regions in nearby galaxies and integrated spectra of more distant galaxies, it has been recently claimed that the DIG can also deeply affect the emission of bright, star-forming galaxies, and that a large correction must be applied to observed line ratios to recover the genuine contribution from H ii regions. Here, we show instead that the e'ect of DIG on the integrated spectra of star-forming galaxies is lower than assumed in previous work. Here we show that, in contrast, aperture effects on the spectroscopy of nearby H ii regions are largely responsible for the observed difference: When spectra of local H ii regions are extracted using large enough apertures while still avoiding the DIG, the observed line ratios are the same as in more distant galaxies. This result is highly relevant for the use of strong-line methods to measure metallicity.
PubDate: Mon, 20 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2648
Issue No: Vol. 508, No. 2 (2021)

• Prospects of direct detection of 48V gamma-rays from thermonuclear
supernovae

Authors: Panther F; Seitenzahl I, Ruiter A, et al.
Pages: 1590 - 1598
Abstract: ABSTRACTDetection of gamma-rays emitted by radioactive isotopes synthesized in stellar explosions can give important insights into the processes that power transients such as supernovae, as well as providing a detailed census of the abundance of different isotope species relevant to the chemical evolution of the Universe. Observations of nearby supernovae have yielded observational proof that 57Co powered the late-time evolution of SN1987A’s light curve, and conclusive evidence that 56Ni and its daughter nuclei power the light curves of Type Ia supernovae. In this paper, we describe the prospects for detecting nuclear decay lines associated with the decay of 48V, the daughter nucleus of 48Cr, which is expected to be synthesized in large quantities – $M_{\mathrm{Cr}}\sim 1.9\times 10^{-2}\, \mathrm{M_\odot }$ – in transients initiated by explosive helium burning (α-capture) of a thick helium shell. We calculate emergent gamma-ray line fluxes for a simulated explosion model of a thermonuclear explosion of carbon–oxygen white dwarf core of mass $0.45\, \mathrm{ M}_{\odot }$ surrounded by a thick helium layer of mass $0.21\, \mathrm{ M}_{\odot }$. We present observational limits on the presence of 48V in nearby SNe Ia 2014J using the INTEGRAL space telescope, excluding a 48Cr production on the surface of more than $0.1\, \mathrm{M_{\odot }}$. We find that the future gamma-ray mission the All-Sky Medium Energy Gamma-Ray Observatory (AMEGO) will have an approximately 5 per cent chance of observing 48V gamma-rays from such events during the currently planned operational lifetime, based on our birthrate predictions of faint thermonuclear transients. We describe the conditions for a 3σ detection by the gamma-ray telescopes INTEGRAL/SPI, Compton Spectrometer and Imager (COSI) , and AMEGO.
PubDate: Thu, 23 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2701
Issue No: Vol. 508, No. 2 (2021)

• First deep images catalogue of extended IPHAS PNe

Authors: Sabin L; Guerrero M, Ramos-Larios G, et al.
Pages: 1599 - 1617
Abstract: ABSTRACTWe present the first instalment of a deep imaging catalogue containing 58 True, Likely, and Possible extended PNe detected with the Isaac Newton Telescope Photometric H α Survey (IPHAS). The three narrow-band filters in the emission lines of H α, [N ii] λ6584 Å, and [O iii] λ5007 Å used for this purpose allowed us to improve our description of the morphology and dimensions of the nebulae. In some cases even the nature of the source has been reassessed. We were then able to unveil new macro- and micro-structures, which will without a doubt contribute to a more accurate analysis of these PNe. It has been also possible to perform a primary classification of the targets based on their ionization level. A Deep Learning classification tool has also been tested. We expect that all the PNe from the IPHAS catalogue of new extended planetary nebulae will ultimately be part of this deep H α, [N ii], and [O iii] imaging catalogue.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2477
Issue No: Vol. 508, No. 2 (2021)

• Asteroseismic fingerprints of stellar mergers

Authors: Rui N; Fuller J.
Pages: 1618 - 1631
Abstract: ABSTRACTStellar mergers are important processes in stellar evolution, dynamics, and transient science. However, it is difficult to identify merger remnant stars because they cannot easily be distinguished from single stars based on their surface properties. We demonstrate that merger remnants can potentially be identified through asteroseismology of red giant stars using measurements of the gravity mode period spacing together with the asteroseismic mass. For mergers that occur after the formation of a degenerate core, remnant stars have overmassive envelopes relative to their cores, which is manifested asteroseismically by a g-mode period spacing smaller than expected for the star’s mass. Remnants of mergers that occur when the primary is still on the main sequence or whose total mass is less than $\approx \! 2 \, {\rm M}_\odot$ are much harder to distinguish from single stars. Using the red giant asteroseismic catalogues of Vrard, Mosser & Samadi and Yu et al., we identify 24 promising candidates for merger remnant stars. In some cases, merger remnants could also be detectable using only their temperature, luminosity, and asteroseismic mass, a technique that could be applied to a larger population of red giants without a reliable period spacing measurement.
PubDate: Thu, 09 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2528
Issue No: Vol. 508, No. 2 (2021)

• improved Master for the LSS: fast and accurate analysis of the two-point
power spectra and correlation functions

Authors: Singh S.
Pages: 1632 - 1651
Abstract: ABSTRACTWe review the methodology for measurements of two-point functions of the cosmological observables, both power spectra and correlation functions. For pseudo-Cℓ estimators, we will argue that the window-weighted overdensity field can yield more optimal measurements as the window acts as an inverse noise weight, an effect that becomes more important for surveys with a variable selection function. We then discuss the impact of approximations made in the Master algorithm and suggest improvements, the iMaster algorithm, which uses the theoretical model to give unbiased results for arbitrarily complex windows provided that the model satisfies weak accuracy conditions. The methodology of iMaster algorithm is also generalized to the correlation functions to reconstruct the binned power spectra, for E/B mode separation, or to properly convolve the correlation functions to account for the scale cuts in the Fourier space model. We also show that the errors in the window estimation lead to both additive and multiplicative effects on the overdensity field. Accurate estimation of window power can be required up to scales of ∼2ℓmax or larger. Mis-estimation of the window power leads to biases in the measured power spectra, which scale as ${\delta C_\ell }\sim M^W_{\ell \ell ^{\prime }}\delta W_{\ell ^{\prime }}$, where the $M^W_{\ell \ell ^{\prime }}$ scales as ∼(2ℓ + 1)Cℓ leading to effects that can be important at high ℓ. While the notation in this paper is geared towards photometric galaxy surveys, the discussion is equally applicable to spectroscopic galaxy, intensity mapping, and Cosmic Microwave Background radiation (CMB) surveys.
PubDate: Mon, 13 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2559
Issue No: Vol. 508, No. 2 (2021)

• The cumulative star formation histories of dwarf galaxies with TNG50. I:
environment-driven diversity and connection to quenching

Authors: Joshi G; Pillepich A, Nelson D, et al.
Pages: 1652 - 1674
Abstract: ABSTRACTWe present the cumulative star formation histories (SFHs) of >15 000 dwarf galaxies ($M_{\rm *}=10^{7-10}\, {\rm M}_{\odot }$) simulated with the TNG50 run of the IllustrisTNG suite across a vast range of environments. The key factors that determine the dwarfs’ SFHs are their central/satellite status and stellar mass, with centrals and more massive dwarfs assembling their stellar mass at later times, on average, compared to satellites and lower mass dwarfs. Satellites (in hosts of mass $M_{\rm 200c, host}=10^{12-14.3}\, {\rm M}_{\odot }$) assembled 90 per cent of their stellar mass ${\sim}7.0_{-5.5}^{+3.3}$ Gyr ago, on average and within the 10th to 90th percentiles, while the centrals did so only ${\sim}1.0_{-0.5}^{+4.0}$ Gyr ago. TNG50 predicts a large diversity in SFHs, so that individual dwarfs can have significantly different cumulative SFHs compared to the stacked median SFHs. Satellite dwarfs with the highest stellar mass to host cluster mass ratios have the latest stellar mass assembly. Conversely, satellites at fixed stellar and host halo mass found closer to the cluster centre or accreted at earlier times show significantly earlier stellar mass assembly. These trends and the shapes of the SFHs themselves are a manifestation of the varying proportions within a given subsample of quenched versus star-forming galaxies, which exhibit markedly distinct SFH shapes. Finally, satellite dwarfs in the most massive hosts have higher SFRs at early times, well before accretion into their z = 0 host, compared to a control sample of centrals mass-matched at the time of accretion. This is the result of the satellites being preprocessed in smaller hosts prior to accretion. Our findings are useful theoretical predictions for comparison to future resolved stellar population observations.
PubDate: Mon, 13 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2573
Issue No: Vol. 508, No. 2 (2021)

• The dispersal of protoplanetary discs – II: photoevaporation models with

Authors: Ercolano B; Picogna G, Monsch K, et al.
Pages: 1675 - 1685
Abstract: ABSTRACTYoung solar-type stars are known to be strong X-ray emitters and their X-ray spectra have been widely studied. X-rays from the central star may play a crucial role in the thermodynamics and chemistry of the circumstellar material as well as in the atmospheric evolution of young planets. In this paper, we present model spectra based on spectral parameters derived from the observations of young stars in the Orion nebula cluster from the Chandra Orion Ultradeep Project (COUP). The spectra are then used to calculate new photoevaporation prescriptions that can be used in disc and planet population synthesis models. Our models clearly show that disc wind mass loss rates are controlled by the stellar luminosity in the soft ($100\, \mathrm{eV}$ to $1\, \mathrm{keV}$) X-ray band. New analytical relations are provided for the mass loss rates and profiles of photoevaporative winds as a function of the luminosity in the soft X-ray band. The agreement between observed and predicted transition disc statistics moderately improved using the new spectra, but the observed population of strongly accreting large cavity discs can still not be reproduced by these models. Furthermore, our models predict a population of non-accreting transition discs that are not observed. This highlights the importance of considering the depletion of millimetre-sized dust grains from the outer disc, which is a likely reason why such discs have not been detected yet.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2590
Issue No: Vol. 508, No. 2 (2021)

• Assessing the sources of reionization: a spectroscopic case study of a
30× lensed galaxy at z ∼ 5 with Lyα, C iv, Mg ii, and [Ne iii]

Authors: Witstok J; Smit R, Maiolino R, et al.
Pages: 1686 - 1700
Abstract: ABSTRACTWe present a detailed spectroscopic analysis of a galaxy at z ≃ 4.88 that is, by chance, magnified ∼30× by gravitational lensing. Only three sources at z ≳ 5 are known with such high magnification. This particular source has been shown to exhibit widespread, high equivalent width ${{\rm C\, \small {IV}}}\ \lambda 1549\, \mathring{\rm A}$ emission, implying it is a unique example of a metal-poor galaxy with a hard radiation field, likely representing the galaxy population responsible for cosmic reionization. Using ultraviolet (UV) nebular line ratio diagnostics, Very Large Telescope (VLT)/X-shooter observations rule out strong active galactic nuclei (AGN) activity, indicating a stellar origin of the hard radiation field instead. We present a new detection of ${[{\rm Ne\, \small {III}}]}\ \lambda 3870\, \mathring{\rm A}$ and use the [${\rm Ne\, \small {III}}$]/[${\rm O\, \small {II}}$] line ratio to constrain the ionization parameter and gas-phase metallicity. Closely related to the commonly used [${\rm O\, \small {III}}$]/[${\rm O\, \small {II}}$] ratio, our [${\rm Ne\, \small {III}}$]/[${\rm O\, \small {II}}$] measurement shows this source is similar to local ‘Green Pea’ galaxies and Lyman-continuum leakers. It furthermore suggests this galaxy is more metal poor than expected from the fundamental metallicity relation, possibly as a consequence of excess gas accretion diluting the metallicity. Finally, we present the highest redshift detection of ${{\rm Mg\, \small {II}}}\ \lambda 2796\, \mathring{\rm A}$, observed at high equivalent width in emission, in contrast to more evolved systems predominantly exhibiting ${\rm Mg\, \small {II}}$ absorption. Strong ${\rm Mg\, \small {II}}$ emission has been observed in most z ∼ 0 Lyman-continuum leakers known and has recently been proposed as an indirect tracer of escaping ionizing radiation. In conclusion, this strongly lensed galaxy, observed just $300\, \mathrm{Myr}$ after reionization ends, enables testing of observational diagnostics proposed to constrain the physical properties of distant galaxies in the James Webb Space Telescope (JWST)/Extremely Large Telescope (ELT) era.
PubDate: Tue, 13 Jul 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2591
Issue No: Vol. 508, No. 2 (2021)

• Probing the physical properties of the intergalactic medium using blazars

Authors: Dalton T; Morris S, Fumagalli M, et al.
Pages: 1701 - 1718
Abstract: ABSTRACTWe use Swift blazar spectra to estimate the key intergalactic medium (IGM) properties of hydrogen column density ($\mathit {N}\small {\rm HXIGM}$), metallicity, and temperature over a redshift range of 0.03 ≤ z ≤ 4.7, using a collisional ionization equilibrium model for the ionized plasma. We adopted a conservative approach to the blazar continuum model given its intrinsic variability and use a range of power-law models. We subjected our results to a number of tests and found that the $\mathit {N}\small {\rm HXIGM}$ parameter was robust with respect to individual exposure data and co-added spectra for each source, and between Swift and XMM–Newton source data. We also found no relation between $\mathit {N}\small {\rm HXIGM}$ and variations in source flux or intrinsic power laws. Though some objects may have a bulk Comptonization component that could mimic absorption, it did not alter our overall results. The $\mathit {N}\small {\rm HXIGM}$ from the combined blazar sample scales as (1 + z)1.8 ± 0.2. The mean hydrogen density at z = 0 is n0 = (3.2 ± 0.5) × 10−7 cm−3. The mean IGM temperature over the full redshift range is log(T/K) =6.1 ± 0.1, and the mean metallicity is [X/H] = −1.62 ± 0.04(Z ∼ 0.02). When combining with the results with a gamma-ray burst (GRB) sample, we find the results are consistent over an extended redshift range of 0.03 ≤ z ≤ 6.3. Using our model for blazars and GRBs, we conclude that the IGM contributes substantially to the total absorption seen in both blazar and GRB spectra.
PubDate: Tue, 14 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2597
Issue No: Vol. 508, No. 2 (2021)

• The dust and gas environment of comet 8P/Tuttle

Authors: Gutiérrez P; Lara L, Moreno F.
Pages: 1719 - 1731
Abstract: ABSTRACTComet 8P/Tuttle has been selected as a possible backup target for the Comet Interceptor mission (ESA). This comet was observed intensively during its previous perihelion passage, in 2008 January. From those observations, important information was obtained about the physical properties of the nucleus and coma. This study focuses on the coma of 8P/Tuttle using visible spectra and images to derive gas and dust production rates. The production rates obtained suggest that this comet can be considered as ‘typical’ concerning the C2/CN and C3/CN ratios, although, depending on the criteria adopted, it could be defined as C3 depleted. NH2 production rates suggest an enrichment of this molecule. Visible and infrared images have been analysed using a Monte Carlo dust tail model. At comparatively large heliocentric distances, the coma is characterized by a dust-to-water ratio around or less than 1. Nevertheless, when the comet approaches perihelion, and the subsolar latitude crosses the equator, the coma dust-to-water ratio increases significantly, reaching values larger than six. Such a high dust-to-gas ratio around perihelion suggests that the nucleus of 8P/Tuttle is also ‘typical’ regarding the refractory content, considering the comparatively high values of that magnitude estimated for different comets.
PubDate: Mon, 13 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2609
Issue No: Vol. 508, No. 2 (2021)

• General-relativistic treatment of tidal g-mode resonances in coalescing
binaries of neutron stars – II. As triggers for precursor flares of
short gamma-ray bursts

Authors: Kuan H; Suvorov A, Kokkotas K.
Pages: 1732 - 1744
Abstract: ABSTRACTIn some short gamma-ray bursts, precursor flares occurring ∼ seconds prior to the main episode have been observed. These flares may then be associated with the last few cycles of the inspiral when the orbital frequency is a few hundred Hz. During these final cycles, tidal forces can resonantly excite quasi-normal modes in the inspiralling stars, leading to a rapid increase in their amplitude. It has been shown that these modes can exert sufficiently strong strains on to the neutron star crust to instigate yieldings. Due to the typical frequencies of g- modes being ∼100 Hz, their resonances with the orbital frequency match the precursor timings and warrant further investigation. Adopting realistic equations of state and solving the general-relativistic pulsation equations, we study g-mode resonances in coalescing quasi-circular binaries, where we consider various stellar rotation rates, degrees of stratification, and magnetic field structures. We show that for some combination of stellar parameters, the resonantly excited g1 and g2 modes may lead to crustal failure and trigger precursor flares.
PubDate: Thu, 16 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2658
Issue No: Vol. 508, No. 2 (2021)

• Advances in control of a pyramid single conjugate adaptive optics system

Authors: Agapito G; Rossi F, Plantet C, et al.
Pages: 1745 - 1755
Abstract: ABSTRACTAdaptive optics systems are an essential technology for the modern astronomy for ground-based telescopes. One of the most recent revolution in the field is the introduction of the pyramid wavefront sensor. The higher performance of this device is paid with increased complexity in the control. In this work, we report about advances in the adaptive optics (AO) system control obtained with SOUL at the Large Binocular Telescope. The first is an improved Tip/Tilt temporal control able to recover the nominal correction even in presence of high temporal frequency resonances. The second one is a modal gain optimization that has been successfully tested on sky for the first time. Pyramid wavefront sensors are the key technology for the first light AO systems of all Extremely Large Telescopes and the reported advances can be relevant contributions for such systems.
PubDate: Fri, 17 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2665
Issue No: Vol. 508, No. 2 (2021)

• Radiation hydrodynamical simulations of the birth of intermediate-mass
black holes in the first galaxies

Authors: Latif M; Khochfar S, Schleicher D, et al.
Pages: 1756 - 1767
Abstract: ABSTRACTThe leading contenders for the seeds of z > 6 quasars are direct-collapse black holes (DCBHs) forming in atomically cooled haloes at z ∼ 20. However, the Lyman–Werner (LW) UV background required to form DCBHs of 105 M⊙ are extreme, about 104 J21, and may have been rare in the early universe. Here we investigate the formation of intermediate-mass black holes (IMBHs) under moderate LW backgrounds of 100 and 500 J21, which were much more common at early times. These backgrounds allow haloes to grow to a few 106–107 M⊙ and virial temperatures of nearly 104 K before collapsing, but do not completely sterilize them of H2. Gas collapse then proceeds via Lyα and rapid H2 cooling at rates that are 10–50 times those in normal Pop III star-forming haloes, but less than those in purely atomically cooled haloes. Pop III stars accreting at such rates become blue and hot, and we find that their ionizing UV radiation limits their final masses to 1800–2800 M⊙ at which they later collapse to IMBHs. Moderate LW backgrounds thus produced IMBHs in far greater numbers than DCBHs in the early universe.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2708
Issue No: Vol. 508, No. 2 (2021)

• How to inflate a wind-blown bubble

Authors: Pittard J; Wareing C, Kupilas M.
Pages: 1768 - 1776
Abstract: ABSTRACTStellar winds are one of several ways that massive stars can affect the star formation process on local and galactic scales. In this paper, we investigate the numerical resolution needed to inflate an energy-driven stellar wind bubble in an external medium. We find that the radius of the wind injection region, rinj, must be below a maximum value, rinj,max, in order for a bubble to be produced, but must be significantly below this value if the bubble properties are to closely agree with analytical predictions. The final bubble momentum is within 25 per cent of the value from a higher resolution reference model if χ = rinj/rinj,max = 0.1. Our work has significance for the amount of radial momentum that a wind-blown bubble can impart to the ambient medium in simulations, and thus on the relative importance of stellar wind feedback.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2712
Issue No: Vol. 508, No. 2 (2021)

• Shocks in the stacked Sunyaev–Zel’dovich profiles of clusters – I.
Analysis with the Three Hundred simulations

Authors: Baxter E; Adhikari S, Vega-Ferrero J, et al.
Pages: 1777 - 1787
Abstract: ABSTRACTGas infalling into the gravitational potential wells of massive galaxy clusters is expected to experience one or more shocks on its journey to becoming part of the intracluster medium (ICM). These shocks are important for setting the thermodynamic properties of the ICM and can therefore impact cluster observables such as X-ray emission and the Sunyaev–Zel’dovich (SZ) effect. We investigate the possibility of detecting signals from cluster shocks in the averaged thermal SZ profiles of galaxy clusters. Using zoom-in hydrodynamic simulations of massive clusters from the Three Hundred Project, we show that if cluster SZ profiles are stacked as a function of R/R200m, shock-induced features appear in the averaged SZ profile. These features are not accounted for in standard fitting formulae for the SZ profiles of galaxy clusters. We show that the shock features should be detectable with samples of clusters from ongoing and future SZ surveys. We also demonstrate that the location of these features is correlated with the cluster accretion rate, as well as the location of the cluster splashback radius. Analyses of ongoing and future surveys, such as SPT-3g, AdvACT, Simons Observatory, and CMB-S4, which include gas shocks will gain a new handle on the properties and dynamics of the outskirts of massive haloes, both in gas and in mass.
PubDate: Thu, 23 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2720
Issue No: Vol. 508, No. 2 (2021)

• GALE xtin: an alternative online tool to determine the interstellar
extinction in the Milky Way

Authors: Amôres E; Jesus R, Moitinho A, et al.
Pages: 1788 - 1797
Abstract: ABSTRACTEstimates of interstellar extinction are essential in a broad range of astronomical research. In the last decades, several maps and models of the large-scale interstellar extinction in the Galaxy have been published. However, these maps and models have been developed in different programming languages, with different user interfaces and input/output formats, which makes using and comparing results from these maps and models difficult. To address this issue, we have developed a tool called GALE xtin (http://www.galextin.org), which estimates interstellar extinction based on both available 3D models/maps and 2D maps. The user only needs to provide a list with coordinates (and distance) and to choose a model/map. GALE xtin will then provide an output list with extinction estimates. It can be implemented in any other portal or model that requires interstellar extinction estimates. Here, a general overview of GALE xtin is presented, along with its capabilities, validation, performance and some results.
PubDate: Thu, 07 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2248
Issue No: Vol. 508, No. 2 (2021)

• The nature of the extreme X-ray variability in the NLS1 1H 0707-495

Authors: Parker M; Alston W, Härer L, et al.
Pages: 1798 - 1816
Abstract: ABSTRACTWe examine archival XMM-Newton data on the extremely variable narrow-line Seyfert 1 active galactic nucleus (AGN) 1H 0707-495. We construct fractional excess variance (Fvar) spectra for each epoch, including the recent 2019 observation taken simultaneously with eROSITA. We explore both intrinsic and environmental absorption origins for the variability in different epochs, and examine the effect of the photoionized emission lines from outflowing gas. In particular, we show that the unusual soft variability first detected by eROSITA in 2019 is due to a combination of an obscuration event and strong suppression of the variance at 1 keV by photoionized emission, which makes the variance below 1 keV appear more extreme. We also examine the variability on long time-scales, between observations, and find that it is well described by a combination of intrinsic variability and absorption variability. We suggest that the typical extreme high frequency variability, which 1H 0707-495 is known for, is intrinsic to the source, but the large amplitude, low frequency variability that causes prolonged low-flux intervals is likely dominated by variable low-ionization, low-velocity absorption.
PubDate: Mon, 30 Aug 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2434
Issue No: Vol. 508, No. 2 (2021)

• Galaxy and mass assembly (GAMA): The environmental impact on SFR and
metallicity in galaxy groups

Authors: Sotillo-Ramos D; Lara-López M, Pérez-García A, et al.
Pages: 1817 - 1830
Abstract: ABSTRACTWe present a study of the relationships and environmental dependencies between stellar mass, star formation rate, and gas metallicity for more than 700 galaxies in groups up to redshift 0.35 from the Galaxy And Mass Assembly (GAMA) survey. To identify the main drivers, our sample was analysed as a function of group-centric distance, projected galaxy number density, and stellar mass. By using control samples of more than 16 000 star-forming field galaxies and volume-limited samples, we find that the highest enhancement in SFR (0.3 dex) occurs in galaxies with the lowest local density. In contrast to previous work, our data show small enhancements of ∼0.1 dex in SFR for galaxies at the highest local densities or group-centric distances. Our data indicates quenching in SFR only for massive galaxies, suggesting that stellar mass might be the main driver of quenching processes for star forming galaxies. We can discard a morphological driven quenching, since the Sérsic index distribution for group and control galaxies are similar. The gas metallicity does not vary drastically. It increases ∼0.08 dex for galaxies at the highest local densities, and decreases for galaxies at the highest group-centric distances, in agreement with previous work. Altogether, the local density, rather than group-centric distance, shows the stronger impact in enhancing both, the SFR and gas metallicity. We applied the same methodology to galaxies from the IllustrisTNG simulations, and although we were able to reproduce the general observational trends, the differences between group and control samples only partially agree with the observations.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2641
Issue No: Vol. 508, No. 2 (2021)

• Signature and escape of highly fractionated plasma in an active region

Authors: Brooks D; Yardley S.
Pages: 1831 - 1841
Abstract: ABSTRACTAccurate forecasting of space weather requires knowledge of the source regions where solar energetic particles (SEP) and eruptive events originate. Recent work has linked several major SEP events in 2014, January, to specific features in the host active region (AR 11944). In particular, plasma composition measurements in and around the footpoints of hot, coronal loops in the core of the active region were able to explain the values later measured in situ by the Wind spacecraft. Due to important differences in elemental composition between SEPs and the solar wind, the magnitude of the Si/S elemental abundance ratio emerged as a key diagnostic of SEP seed population and solar wind source locations. We seek to understand if the results are typical of other active regions, even if they are not solar wind sources or SEP productive. In this paper, we use a novel composition analysis technique, together with an evolutionary magnetic field model, in a new approach to investigate a typical solar active region (AR 11150), and identify the locations of highly fractionated (high Si/S abundance ratio) plasma. Material confined near the footpoints of coronal loops, as in AR 11944, that in this case have expanded to the AR periphery, show the signature, and can be released from magnetic field opened by reconnection at the AR boundary. Since the fundamental characteristics of closed field loops being opened at the AR boundary is typical of active regions, this process is likely to be general.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2681
Issue No: Vol. 508, No. 2 (2021)

• On the terminal spins of accreting stars and planets: boundary layers

Authors: Dittmann A.
Pages: 1842 - 1852
Abstract: ABSTRACTThe origin of the spins of giant planets is an open question in astrophysics. As planets and stars accrete from discs, if the specific angular momentum accreted corresponds to that of a Keplerian orbit at the surface of the object, it is possible for planets and stars to be spun-up to near-break-up speeds. However, accretion cannot proceed on to planets and stars in the same way that accretion proceeds through the disc. For example, the magneto-rotational instability cannot operate in the region between the nearly Keplerian disc and more slowly rotating surface because of the sign of the angular velocity gradient. Through this boundary layer where the angular velocity sharply changes, mass and angular momentum transport is thought to be driven by acoustic waves generated by global supersonic shear instabilities and vortices. We present the first study of this mechanism for angular momentum transport around rotating stars and planets using 2D vertically integrated moving-mesh simulations of ideal hydrodynamics. We find that above rotation rates of ∼0.4−0.6 times the Keplerian rate at the surface the rate at which angular momentum is transported inwards through the boundary layer by waves decreases by ∼1−3 orders of magnitude depending on the gas sound speed. We also find that the accretion rate through the boundary layer decreases commensurately and becomes less variable for faster rotating objects. Our results provide a purely hydrodynamic mechanism for limiting the spins of accreting planets and stars to factors of a few less than the break-up speed.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2682
Issue No: Vol. 508, No. 2 (2021)

• The mean free path of ionizing photons at 5 < z < 6: evidence for
rapid evolution near reionization

Authors: Becker G; D’Aloisio A, Christenson H, et al.
Pages: 1853 - 1869
Abstract: ABSTRACTThe mean free path of ionizing photons, λmfp, is a key factor in the photoionization of the intergalactic medium (IGM). At z ≳ 5, however, λmfp may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of λmfp that address this bias and extend up to z ∼ 6 for the first time. Our measurements at z ∼ 5 are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At z ∼ 6 we use QSO spectra from Keck ESI and VLT X-Shooter. We measure $\lambda _{\rm mfp} = 9.09^{+1.62}_{-1.28}$ proper Mpc and $0.75^{+0.65}_{-0.45}$ proper Mpc (68 per cent confidence) at z = 5.1 and 6.0, respectively. The results at z = 5.1 are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At z = 6.0, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at z = 6.0 falls well below extrapolations from lower redshifts, indicating rapid evolution in λmfp over 5 < z < 6. This evolution disfavours models in which reionization ended early enough that the IGM had time to fully relax hydrodynamically by z = 6, but is qualitatively consistent with models wherein reionization completed at z = 6 or even significantly later. Our mean free path results are most consistent with late reionization models wherein the IGM is still 20 per cent neutral at z = 6, although our measurement at z = 6.0 is even lower than these models prefer.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2696
Issue No: Vol. 508, No. 2 (2021)

• AutoProf – I. An automated non-parametric light profile pipeline for
modern galaxy surveys

Authors: Stone C; Arora N, Courteau S, et al.
Pages: 1870 - 1887
Abstract: ABSTRACTWe present an automated non-parametric light profile extraction pipeline called autoprof. All steps for extracting surface brightness (SB) profiles are included in autoprof, allowing streamlined analyses of galaxy images. autoprof improves upon previous non-parametric ellipse fitting implementations with fit-stabilization procedures adapted from machine learning techniques. Additional advanced analysis methods are included in the flexible pipeline for the extraction of alternative brightness profiles (along radial or axial slices), smooth axisymmetric models, and the implementation of decision trees for arbitrarily complex pipelines. Detailed comparisons with widely used photometry algorithms (photutils, xvista, and galfit) are also presented. These comparisons rely on a large collection of late-type galaxy images from the PROBES catalogue. The direct comparison of SB profiles shows that autoprof can reliably extract fainter isophotes than other methods on the same images, typically by >2 mag arcsec−2. Contrasting non-parametric elliptical isophote fitting with simple parametric models also shows that two-component fits (e.g. Sérsic plus exponential) are insufficient to describe late-type galaxies with high fidelity. It is established that elliptical isophote fitting, and in particular autoprof, is ideally suited for a broad range of automated isophotal analysis tasks. autoprof is freely available to the community at: https://github.com/ConnorStoneAstro/AutoProf.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2709
Issue No: Vol. 508, No. 2 (2021)

• Ion acceleration to 100 keV by the ExB wave mechanism in
collision-less shocks

Authors: Stasiewicz K; Eliasson B.
Pages: 1888 - 1896
Abstract: ABSTRACTIt is shown that ions can be accelerated to about 100 keV in the direction perpendicular to the magnetic field by the ExB mechanism of electrostatic waves. The acceleration occurs in discrete steps of duration being a small fraction of the gyroperiod and can explain observations of ion energization to 10 keV at quasi-perpendicular shocks and to hundreds keV at quasi-parallel shocks. A general expression is provided for the maximum energy of ions accelerated in shocks of arbitrary configuration. The waves involved in the acceleration are related to three cross-field current-driven instabilities: the lower hybrid drift (LHD) instability induced by the density gradients in shocks and shocklets, followed by the modified two-stream (MTS) and electron cyclotron drift (ECD) instabilities, induced by the ExB drift of electrons in the strong LHD wave electric field. The ExB wave mechanism accelerates heavy ions to energies proportional to the atomic mass number, which is consistent with satellite observations upstream of the bow shock and also with observations of post-shocks in supernovae remnants. The results are compared with other acceleration mechanisms traditionally discussed in the literature.
PubDate: Fri, 24 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2739
Issue No: Vol. 508, No. 2 (2021)

• Measuring the baryonic Tully–Fisher relation below the detection
threshold

Authors: Pan H; Jarvis M, Ponomareva A, et al.
Pages: 1897 - 1907
Abstract: ABSTRACTWe present a novel 2D flux density model for observed H i emission lines combined with a Bayesian stacking technique to measure the baryonic Tully–Fisher relation below the nominal detection threshold. We simulate a galaxy catalogue, which includes H i lines described with either Gaussian or busy function profiles, and H i data cubes with a range of noise and survey areas similar to the MeerKAT International Giga-Hertz Tiered Extragalactic Exploration (MIGHTEE) survey. With prior knowledge of redshifts, stellar masses, and inclinations of spiral galaxies, we find that our model can reconstruct the input baryonic Tully–Fisher parameters (slope and zero-point) most accurately in a relatively broad redshift range from the local Universe to z = 0.3 for all the considered levels of noise and survey areas and up to z = 0.55 for a nominal noise of 90 $\mu$Jy/channel over 5 deg2. Our model can also determine the $M_{\rm H\, \small {I}} - M_{\star }$ relation for spiral galaxies beyond the local Universe and account for the detailed shape of the H i emission line, which is crucial for understanding the dynamics of spiral galaxies. Thus, we have developed a Bayesian stacking technique for measuring the baryonic Tully–Fisher relation for galaxies at low stellar and/or H i masses and/or those at high redshift, where the direct detection of H i requires prohibitive exposure times.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2601
Issue No: Vol. 508, No. 2 (2021)

• Fine and hyperfine excitation of nitric oxide by collision with para-H2 at
low temperature

Authors: Ben Khalifa M; Loreau J.
Pages: 1908 - 1914
Abstract: ABSTRACTNitric oxide is an open-shell molecule abundantly detected in the interstellar medium. A precise modelling of its radiative and collisional processes opens the path to a precise estimate of its abundance. We present here the first rate coefficients for fine and hyperfine (de-)excitation of NO by collisions with the most ubiquitous collision partner in the interstellar medium, para-H2 hydrogen molecules, using a recently developed accurate interaction potential. We report quantum scattering calculations for transitions involving the first 74 fine levels and the corresponding 442 hyperfine levels belonging to both F1 and F2 spin–orbit manifolds. To do so, we have calculated cross-sections by means of the quantum mechanical close-coupling approach up to 1000 cm−1 of total energy and rate coefficients from 5 to 100 K. Propensity rules are discussed and the new NO–H2 rates are compared to those available in the literature, based on scaled NO–He rates. Large differences are observed between the two sets of rate coefficients, and this comparison shows that the new collision rates must be used in interpreting NO emission lines. We also examined the effect of these new rates on the NO excitation in cold clouds by performing radiative transfer calculations of the excitation and brightness temperatures for the two NO lines at 150.176 and 250.4368 GHz. This shows that the local thermodynamic equilibrium is not fulfilled for this species for typical conditions. We expect the use of the rates presented in this study to improve the constraints on the abundance of NO.
PubDate: Mon, 20 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2630
Issue No: Vol. 508, No. 2 (2021)

• Lyman-alpha emitters and the 21 cm power spectrum as probes of
density–ionization correlation in the epoch of reionization

Authors: Pagano M; Liu A.
Pages: 1915 - 1928
Abstract: ABSTRACTDue to the large cross-section of Ly α photons with hydrogen, Lyman-alpha emitters (LAEs) are sensitive to the presence of neutral hydrogen in the intergalactic medium (IGM) during the epoch of reionization (EoR): the period in the Universe’s history where neutral hydrogen in the IGM is ionized. The type of correlation between the ionized regions of the IGM with respect to the underlying intrinsic LAEs has a pronounced effect on the number of observed LAEs and their apparent clustering. As a result, observations of LAEs during the EoR can be used as a probe of the EoR morphology. Here, we build on previous works where we parametrize the density–ionization correlation during the EoR, and study how the observed number density and angular correlation function (ACF) of LAEs depend on this parametrization. Using Subaru measurements of the number density of LAEs and their ACF at z = 6.6, we place constraints on the EoR morphology. We find that measurements of LAEs at z = 6.6 alone cannot distinguish between different density–ionization models at $68{{\ \rm per\ cent}}$ credibility. However, adding information regarding the number density, and ACF, of LAEs at z = 6.6 to 21 cm power spectrum measurements using the hydrogen Epoch of Reionization Array at the mid-point of reionization can rule out uncorrelated and outside-in reionization at $99{{\ \rm per\ cent}}$ credibility.
PubDate: Thu, 16 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2656
Issue No: Vol. 508, No. 2 (2021)

• The Galactic neutron star population – I. An extragalactic view of the
Milky Way and the implications for fast radio bursts

Authors: Chrimes A; Levan A, Groot P, et al.
Pages: 1929 - 1946
Abstract: ABSTRACTA key tool astronomers have to investigate the nature of extragalactic transients is their position on their host galaxies. Galactocentric offsets, enclosed fluxes, and the fraction of light statistic are widely used at different wavelengths to help infer the nature of transient progenitors. Motivated by the proposed link between magnetars and fast radio bursts (FRBs), we create a face-on image of the Milky Way using best estimates of its size, structure, and colour. We place Galactic magnetars, pulsars, low-mass, and high-mass X-ray binaries on this image, using the available distance information. Galactocentric offsets, enclosed fluxes, and fraction of light distributions for these systems are compared to extragalactic transient samples. We find that FRBs follow the distributions for Galactic neutron stars closest, with 24 (75 per cent) of the Anderson–Darling tests we perform having a p-value greater than 0.05. This suggests that FRBs are located on their hosts in a manner consistent with Galactic neutron stars on the Milky Way’s light, although we cannot determine which specific neutron star population is the best match. The Galactic distributions are consistent with other extragalactic transients much less often across the range of comparisons made, with type Ia SNe in second place, at only 33 per cent of tests exceeding 0.05. Overall, our results provide further support for FRB models invoking isolated young neutron stars, or binaries containing a neutron star.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2676
Issue No: Vol. 508, No. 2 (2021)

• Narrow-band giant pulses from the Crab pulsar

Authors: Thulasiram P; Lin H.
Pages: 1947 - 1953
Abstract: ABSTRACTWe used a new spectral-fitting technique to identify a subpopulation of 6 narrow-band giant pulses from the Crab pulsar out of a total of 1578. These giant pulses were detected in 77 min of observations with the 46-m dish at the Algonquin Radio Observatory at 400–800 MHz. The narrow-band giant pulses consist of both main- and inter-pulses, thereby being more likely to be caused by an intrinsic emission mechanism as opposed to a propagation effect. Fast radio bursts (FRBs) have demonstrated similar narrow-band features, while only little has been observed in the giant pulses of pulsars. We report the narrow-band giant pulses with Δν/ν of the order of 0.1, which is close to the value of 0.05 reported for the repeater FRB 20190711A. Hence, the connection between FRBs and giant pulses of pulsars is further established.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2692
Issue No: Vol. 508, No. 2 (2021)

• Revealing the formation histories of the first stars with the cosmic
near-infrared background

Authors: Sun G; Mirocha J, Mebane R, et al.
Pages: 1954 - 1972
Abstract: ABSTRACTThe cosmic near-infrared background (NIRB) offers a powerful integral probe of radiative processes at different cosmic epochs, including the pre-reionization era when metal-free, Population III (Pop III) stars first formed. While the radiation from metal-enriched, Population II (Pop II) stars likely dominates the contribution to the observed NIRB from the reionization era, Pop III stars – if formed efficiently – might leave characteristic imprints on the NIRB, thanks to their strong Lyα emission. Using a physically motivated model of first star formation, we provide an analysis of the NIRB mean spectrum and anisotropy contributed by stellar populations at z > 5. We find that in circumstances where massive Pop III stars persistently form in molecular cooling haloes at a rate of a few times $10^{-3}\, \mathrm{ M}_\odot \ \mathrm{yr}^{-1}$, before being suppressed towards the epoch of reionization (EoR) by the accumulated Lyman–Werner background, a unique spectral signature shows up redward of $1\, \mu$m in the observed NIRB spectrum sourced by galaxies at z > 5. While the detailed shape and amplitude of the spectral signature depend on various factors including the star formation histories, initial mass function, LyC escape fraction and so forth, the most interesting scenarios with efficient Pop III star formation are within the reach of forthcoming facilities, such as the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer. As a result, new constraints on the abundance and formation history of Pop III stars at high redshifts will be available through precise measurements of the NIRB in the next few years.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2697
Issue No: Vol. 508, No. 2 (2021)

• Seeds don’t sink: even massive black hole ‘seeds’ cannot migrate to
galaxy centres efficiently

Authors: Ma L; Hopkins P, Ma X, et al.
Pages: 1973 - 1985
Abstract: ABSTRACTPossible formation scenarios of supermassive black holes (BHs) in the early universe include rapid growth from less massive seed BHs via super-Eddington accretion or runaway mergers, yet both of these scenarios would require seed BHs to efficiently sink to and be trapped in the Galactic Centre via dynamical friction. This may not be true for their complicated dynamics in clumpy high-z galaxies. In this work, we study this ‘sinking problem’ with state-of-the-art high-resolution cosmological simulations, combined with both direct N-body integration of seed BH trajectories and post-processing of randomly generated test particles with a newly developed dynamical friction estimator. We find that seed BHs less massive than $10^8\, \mathrm{M}_\odot$ (i.e. all but the already-supermassive seeds) cannot efficiently sink in typical high-z galaxies. We also discuss two possible solutions: dramatically increasing the number of seeds such that one seed can end up trapped in the Galactic Centre by chance, or seed BHs being embedded in dense structures (e.g. star clusters) with effective masses above the mass threshold. We discuss the limitations of both solutions.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2713
Issue No: Vol. 508, No. 2 (2021)

• Temporal and spectral study of PKS B1222 + 216 flares in 2014

Authors: Chatterjee A; Roy A, Sarkar A, et al.
Pages: 1986 - 2001
Abstract: ABSTRACTWe report on a temporal and spectral study of a flat-spectrum radio quasar, PKS B1222 + 216, in a flare state to get insight into the acceleration and emission mechanisms inside the jet. It is one of the brightest and highly active blazars in the MeV–GeV regime. The long-term multiwaveband light curves of this object showed flaring activity in 2014, with two distinct flares. The work presented here includes the study of flux-index variation, flare fitting, and hardness ratio, and the spectral modelling of X-ray and γ-ray data. The flux-index correlation found in the MeV–GeV regime indicates a ‘softer when brighter’ feature. The modelling of γ-ray light curves suggests that low-energy particles initiate both the flares, followed by the injection of high-energy particles. The short rise time indicates the presence of Fermi first-order acceleration. A single-zone leptonic model is used to fit the multiwaveband spectral energy distributions generated for both flares. The spectral energy distribution modelling shows that inverse Compton scattering of the photon field reprocessed from the broad-line region primarily accounts for the GeV emission. In addition, we have reported a shift in the break energy in the soft X-ray regime during flares, which is due to a rapid change in the injection spectrum.
PubDate: Fri, 08 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2747
Issue No: Vol. 508, No. 2 (2021)

• Outbursts and stellar properties of the classical Be star HD 6226

Authors: Richardson N; Thizy O, Bjorkman J, et al.
Pages: 2002 - 2018
Abstract: ABSTRACTThe bright and understudied classical Be star HD 6226 has exhibited multiple outbursts in the last several years during which the star grew a viscous decretion disc. We analyse 659 optical spectra of the system collected from 2017 to 2020, along with a ultraviolet spectrum from the Hubble Space Telescope and high cadence photometry from both Transiting Exoplanet Survey Satellite (TESS) and the Kilodegree Extremely Little Telescope (KELT) survey. We find that the star has a spectral type of B2.5IIIe, with a rotation rate of 74 per cent of critical. The star is nearly pole-on with an inclination of 13${_{.}^{\circ}}$4. We confirm the spectroscopic pulsational properties previously reported, and report on three photometric oscillations from KELT photometry. The outbursting behaviour is studied with equivalent width measurements of H α and H β, and the variations in both of these can be quantitatively explained with two frequencies through a Fourier analysis. One of the frequencies for the emission outbursts is equal to the difference between two photometric oscillations, linking these pulsation modes to the mass ejection mechanism for some outbursts. During the TESS observation time period of 2019 October 7 to 2019 November 2, the star was building a disc. With a large data set of H α and H β spectroscopy, we are able to determine the time-scales of dissipation in both of these lines, similar to past work on Be stars that has been done with optical photometry. HD 6226 is an ideal target with which to study the Be disc-evolution given its apparent periodic nature, allowing for targeted observations with other facilities in the future.
PubDate: Mon, 27 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2759
Issue No: Vol. 508, No. 2 (2021)

• LeMMINGs III. The e-MERLIN legacy survey of the Palomar sample: exploring
the origin of nuclear radio emission in active and inactive galaxies
through the [O iii] – radio connection

Authors: Baldi R; Williams D, Beswick R, et al.
Pages: 2019 - 2038
Abstract: ABSTRACTWhat determines the nuclear radio emission in local galaxies' To address this question, we combine optical [O iii] line emission, robust black hole (BH) mass estimates, and high-resolution e-MERLIN 1.5-GHz data, from the LeMMINGs survey, of a statistically complete sample of 280 nearby optically active (LINER and Seyfert) and inactive [H ii and absorption line galaxies (ALGs)] galaxies. Using [O iii] luminosity ($L_{\rm [O\, \small {III}]}$) as a proxy for the accretion power, local galaxies follow distinct sequences in the optical–radio planes of BH activity, which suggest different origins of the nuclear radio emission for the optical classes. The 1.5-GHz radio luminosity of their parsec-scale cores (Lcore) is found to scale with BH mass (MBH) and [O iii] luminosity. Below MBH ∼ 106.5 M⊙, stellar processes from non-jetted H ii galaxies dominate with $L_{\rm core} \propto M_{\rm BH}^{0.61\pm 0.33}$ and $L_{\rm core} \propto L_{\rm [O\, \small {III}]}^{0.79\pm 0.30}$. Above MBH ∼ 106.5 M⊙, accretion-driven processes dominate with $L_{\rm core} \propto M_{\rm BH}^{1.5-1.65}$ and $L_{\rm core} \propto L_{\rm [O\, \small {III}]}^{0.99-1.31}$ for active galaxies: radio-quiet/loud LINERs, Seyferts, and jetted H ii galaxies always display (although low) signatures of radio-emitting BH activity, with $L_{\rm 1.5\, GHz}\gtrsim 10^{19.8}$ W Hz−1 and MBH ≳ 107 M⊙, on a broad range of Eddington-scaled accretion rates ($\dot{m}$). Radio-quiet and radio-loud LINERs are powered by low-$\dot{m}$ discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-$\dot{m}$ discs account for the compact and edge-brightened jets of Seyferts, respectively. Jetted H ii galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. In conclusion, specific accretion–ejection states of active BHs determine the radio production and the optical classification of local active galaxies.
PubDate: Fri, 15 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2613
Issue No: Vol. 508, No. 2 (2021)

• Deep learning applications based on SDSS photometric data: detection and
classification of sources

Authors: He Z; Qiu B, Luo A, et al.
Pages: 2039 - 2052
Abstract: ABSTRACTMost astronomical source classification algorithms based on photometric data struggle to classify sources as quasars, stars, and galaxies reliably. To achieve this goal and build a new Sloan Digital Sky Survey photometric catalogue in the future, we apply a deep learning source detection network built on YOLO v4 object detection framework to detect sources and design a new deep learning classification network named APSCnet (astronomy photometric source classification network) to classify sources. In addition, a photometric background image generation network is applied to generate background images in the process of data sets synthesis. Our detection network obtains a mean average precision score of 88.02 when IOU = 0.5. As for APSCnet, in a magnitude range with 14–25, we achieve a precision of 84.1 ${{\ \rm per\ cent}}$ at 93.2 ${{\ \rm per\ cent}}$ recall for quasars, a precision of 94.5 ${{\ \rm per\ cent}}$ at 84.6 ${{\ \rm per\ cent}}$ recall for stars, and a precision of 95.8 ${{\ \rm per\ cent}}$ at 95.1 ${{\ \rm per\ cent}}$ recall for galaxies; and in a magnitude range with less than 20, we achieve a precision of 96.6 ${{\ \rm per\ cent}}$ at 94.7${{\ \rm per\ cent}}$ recall for quasars, a precision of 95.7${{\ \rm per\ cent}}$ at 97.4${{\ \rm per\ cent}}$ recall for stars, and a precision of 98.9 ${{\ \rm per\ cent}}$ at 99.2 ${{\ \rm per\ cent}}$ recall for galaxies. We have proved the superiority of our algorithm in the classification of astronomical sources through comparative experiments between multiple sets of methods. In addition, we also analysed the impact of point spread function on the classification results. These technologies may be applied to data mining of the next generation sky surveys, such as LSST, WFIRST, and CSST etc.
PubDate: Wed, 04 Aug 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2243
Issue No: Vol. 508, No. 2 (2021)

• Widely distributed exogenic materials of varying compositions and
morphologies on asteroid (101955) Bennu

Authors: Tatsumi E; Popescu M, Campins H, et al.
Pages: 2053 - 2070
Abstract: ABSTRACTUsing the multiband imager MapCam on board the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft, we identified 77 instances of proposed exogenic materials distributed globally on the surface of the B-type asteroid (101955) Bennu. We identified materials as exogenic on the basis of an absorption near 1 $\mu$m that is indicative of anhydrous silicates. The exogenic materials are spatially resolved by the telescopic camera PolyCam. All such materials are brighter than their surroundings, and they are expressed in a variety of morphologies: homogeneous, breccia-like, inclusion-like, and others. Inclusion-like features are the most common. Visible spectrophotometry was obtained for 46 of the 77 locations from MapCam images. Principal component analysis indicates at least two trends: (i) mixing of Bennu's average spectrum with a strong 1-$\mu$m band absorption, possibly from pyroxene-rich material, and (ii) mixing with a weak 1-$\mu$m band absorption. The end member with a strong 1-$\mu$m feature is consistent with Howardite-Eucrite-Diogenite (HED) meteorites, whereas the one showing a weak 1-$\mu$m feature may be consistent with HEDs, ordinary chondrites, or carbonaceous chondrites. The variation in the few available near-infrared reflectance spectra strongly suggests varying compositions among the exogenic materials. Thus, Bennu might record the remnants of multiple impacts with different compositions to its parent body, which could have happened in the very early history of the Solar system. Moreover, at least one of the exogenic objects is compositionally different from the exogenic materials found on the similar asteroid (162173) Ryugu, and they suggest different impact tracks.
PubDate: Mon, 13 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2548
Issue No: Vol. 508, No. 2 (2021)

• Shock and splash: gas and dark matter halo boundaries around ΛCDM
galaxy clusters

Authors: Aung H; Nagai D, Lau E.
Pages: 2071 - 2078
Abstract: ABSTRACTRecent advances in simulations and observations of galaxy clusters suggest that there exists a physical outer boundary of massive cluster-size dark matter (DM) haloes. In this work, we investigate the locations of the outer boundaries of DM and gas around cluster-size DM haloes, by analysing a sample of 65 massive DM haloes extracted from the Omega500 zoom-in hydrodynamical cosmological simulations. We show that the location of accretion shock is offset from that of the DM splashback radius, contrary to the prediction of the self-similar models. The accretion shock radius is larger than all definitions of the splashback radius in the literature by $20-100{{\ \rm per\ cent}}$. The accretion shock radius defined using the steepest drop in the entropy and pressure profiles is approximately 1.89 times larger than the splashback radius defined by the steepest slope in the DM density profile, and it is ≈1.2 times larger than the edge of the DM phase space structure. We discuss implications of our results for multiwavelength studies of galaxy clusters.
PubDate: Thu, 23 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2598
Issue No: Vol. 508, No. 2 (2021)

• Periodic activity from fast radio burst FRB180916 explained in the frame
of the orbiting asteroid model

Authors: Voisin G; Mottez F, Zarka P.
Pages: 2079 - 2089
Abstract: ABSTRACTObservation of fast radio bursts (FRBs) are rising very quickly with the advent of specialized instruments and surveys, and it has recently been shown that some of them repeat quasi-periodically. In particular, evidence of a P = 16.35 d period has been reported for FRB 180916.J0158+65. We seek an explanation within the frame of our orbiting asteroid model, whereby FRBs are produced in the plasma wake of asteroids immersed in the wind of a pulsar or a magnetar. We used the data reported by the CHIME/FRB collaboration in order to infer the orbital characteristics of asteroid swarms, and performed parametric studies to explore the possible characteristics of the pulsar, its wind, and of the asteroids, under the constraint that the latter remain dynamically and thermally stable. We found a plausible configuration in which a young pulsar is orbited by a main ∼10−3 M⊙ companion with a period 3P = 49 d, three times longer than the apparent periodicity P. Asteroids responsible for FRBs are located in three dynamical swarms near the L3, L4, and L5 Lagrange points, in a 2:3 orbital resonance akin to the Hildas class of asteroids in the Solar system. In addition, asteroids could be present in the Trojan swarms at the L4 and L5 Lagrange points. Together, these swarms form a carousel that explains the apparent P periodicity and dispersion. We estimated that the presence of at least a few thousand asteroids, of size ∼20 km, is necessary to produce the observed burst rate. We show how radius-to-frequency mapping in the wind and small perturbations by turbulence can suffice to explain downward-drifting sub-pulses, micro-structures, and narrow spectral occupancy.
PubDate: Fri, 17 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2622
Issue No: Vol. 508, No. 2 (2021)

• Density estimation with Gaussian processes for gravitational wave
posteriors

Authors: D’Emilio V; Green R, Raymond V.
Pages: 2090 - 2097
Abstract: ABSTRACTThe properties of black hole and neutron-star binaries are extracted from gravitational waves (GW) signals using Bayesian inference. This involves evaluating a multidimensional posterior probability function with stochastic sampling. The marginal probability distributions of the samples are sometimes interpolated with methods such as kernel density estimators. Since most post-processing analysis within the field is based on these parameter estimation products, interpolation accuracy of the marginals is essential. In this work, we propose a new method combining histograms and Gaussian processes (GPs) as an alternative technique to fit arbitrary combinations of samples from the source parameters. This method comes with several advantages such as flexible interpolation of non-Gaussian correlations, Bayesian estimate of uncertainty, and efficient resampling with Hamiltonian Monte Carlo.
PubDate: Mon, 20 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2623
Issue No: Vol. 508, No. 2 (2021)

• A panoramic view of the Local Group dwarf galaxy NGC 6822

Authors: Zhang S; Mackey D, Da Costa G.
Pages: 2098 - 2113
Abstract: ABSTRACTWe present a panoramic survey of the isolated Local Group dwarf irregular galaxy NGC 6822. Our photometry reaches ∼2–3 mag deeper than most previous studies and spans the widest area around the dwarf compared to any prior work. We observe no stellar overdensities in the outskirts of NGC 6822 to V ∼ 30 mag arcsec−2 and a projected radius of 16.5 kpc. This indicates that NGC 6822 has not experienced any recent interaction with a companion galaxy, despite previous suggestions to the contrary. Similarly, we find no evidence for any dwarf satellites of NGC 6822 to a limiting luminosity MV ≈ −5. NGC 6822 contains a disc of H i gas and young stars, oriented at ∼60○ to an extended spheroid composed of old stellar populations. We observe no correlation between the distribution of young stars and spheroid members. Our imaging allows us to trace the spheroid to nearly 11 kpc along its major axis, commensurate with the extent of the NGC 6822 globular cluster system. We find that the spheroid becomes increasingly flattened at larger radii, and its position angle twists by up to 40○. We use Gaia EDR3 astrometry to measure a proper motion for NGC 6822, and then sample its orbital parameter space. While this galaxy has spent the majority of its life in isolation, we find that it likely passed within the virial radius of the Milky Way ∼3–4 Gyr ago. This may explain the apparent flattening and twisting observed in the outskirts of its spheroid.
PubDate: Wed, 15 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2642
Issue No: Vol. 508, No. 2 (2021)

• Parker Solar Probe observations of helical structures as boundaries for
energetic particles

Authors: Pecora F; Servidio S, Greco A, et al.
Pages: 2114 - 2122
Abstract: ABSTRACTEnergetic particle transport in the interplanetary medium is known to be affected by magnetic structures. It has been demonstrated for solar energetic particles in near-Earth orbit studies, and also for the more energetic cosmic rays. In this paper, we show observational evidence that intensity variations of solar energetic particles can be correlated with the occurrence of helical magnetic flux tubes and their boundaries. The analysis is carried out using data from Parker Solar Probe orbit 5, in the period 2020 May 24 to June 2. We use FIELDS magnetic field data and energetic particle measurements from the Integrated Science Investigation of the Sun (IS⊙IS) suite on the Parker Solar Probe. We identify magnetic flux ropes by employing a real-space evaluation of magnetic helicity, and their potential boundaries using the Partial Variance of Increments method. We find that energetic particles are either confined within or localized outside of helical flux tubes, suggesting that the latter act as transport boundaries for particles, consistent with previously developed viewpoints.
PubDate: Fri, 17 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2659
Issue No: Vol. 508, No. 2 (2021)

• Thermonuclear X-ray bursts from 4U 1636 − 536
observed with AstroSat

Authors: Roy P; Beri A, Bhattacharyya S.
Pages: 2123 - 2133
Abstract: ABSTRACTWe report results obtained from the study of 12 thermonuclear X-ray bursts in six AstroSat observations of a neutron star X-ray binary and well-known X-ray burster, 4U 1636 − 536. Burst oscillations (BOs) at ∼ 581 Hz are observed with 4–5σ confidence in three of these X-ray bursts. The rising phase BOs show a decreasing trend of the fractional rms amplitude at 3σ confidence, by far the strongest evidence of thermonuclear flame spreading observed with AstroSat. During the initial 0.25 s of the rise a very high value ($34.0\pm 6.7{{{\ \rm per\ cent}}}$) is observed. The concave shape of the fractional amplitude profile provides a strong evidence of latitude-dependent flame speeds, possibly due to the effects of the Coriolis force. We observe decay phase oscillations with amplitudes comparable to that observed during the rising phase, plausibly due to the combined effect of both surface modes, as well as the cooling wake. The Doppler shifts due to the rapid rotation of the neutron star might cause hard pulses to precede the soft pulses, resulting in a soft lag. The distance to the source estimated using the photospheric radius expansion bursts is consistent with the known value of ∼6 kpc.
PubDate: Mon, 20 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2680
Issue No: Vol. 508, No. 2 (2021)

• Plasma screening of nuclear fusion reactions in liquid layers of compact
degenerate stars: a first-principle study

Authors: Baiko D.
Pages: 2134 - 2141
Abstract: ABSTRACTA reliable description of nuclear fusion reactions in inner layers of white dwarfs and envelopes of neutron stars is important for realistic modelling of a wide range of observable astrophysical phenomena from accreting neutron stars to Type Ia supernovae. We study the problem of screening of the Coulomb barrier impeding the reactions by a plasma surrounding the fusing nuclei. Numerical calculations of the screening factor are performed from the first principles with the aid of quantum-mechanical path integrals in the model of a one-component plasma of atomic nuclei for temperatures and densities typical for dense liquid layers of compact degenerate stars. We do not rely on various quasi-classic approximations widely used in the literature, such as factoring out the tunnelling process, tunnelling in an average spherically symmetric mean-force potential, usage of classic free energies and pair correlation functions, linear mixing rule, and so on. In general, a good agreement with earlier results from the thermonuclear limit to Γ ∼ 100 is found. For a very strongly coupled liquid 100 ≲ Γ ≤ 175, a deviation from currently used parametrizations of the reaction rates is discovered and approximated by a simple analytic expression. The developed method of nuclear reaction rate calculations with account of plasma screening can be extended to ion mixtures and crystallized phases of stellar matter.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2702
Issue No: Vol. 508, No. 2 (2021)

• Formation and evolution of protostellar accretion discs – II. From 3D
simulation to a simple semi-analytic model of Class 0/I discs

Authors: Xu W; Kunz M.
Pages: 2142 - 2168
Abstract: ABSTRACTWe use a 3D radiative non-ideal magnetohydrodynamic simulation to investigate the formation and evolution of a young protostellar disc from a magnetized pre-stellar core. The simulation covers the first ${\sim }10\, {\rm kyr}$ after protostar formation and shows a massive, weakly magnetized disc with radius that initially grows and then saturates at ${\sim }30\, {\rm au}$. The disc is gravitationally unstable with prominent large-amplitude spiral arms. We use our simulation results and a series of physical arguments to construct a predictive and quantitative physical picture of Class 0/I protostellar disc evolution from several aspects, including (i) the angular-momentum redistribution in the disc, self-regulated by gravitational instability to make most of the disc marginally unstable; (ii) the thermal profile of the disc, well-approximated by a balance between radiative cooling and accretion heating; and (iii) the magnetic-field strength and magnetic-braking rate inside the disc, regulated by non-ideal magnetic diffusion. Using these physical insights, we build a simple 1D semi-analytic model of disc evolution. We show that this 1D model, when coupled to a computationally inexpensive simulation for the evolution of the surrounding pseudo-disc, can be used reliably to predict disc evolution in the Class 0/I phase. The predicted long-term evolution of disc size, which saturates at ${\sim }30\, {\rm au}$ and eventually shrinks, is consistent with a recent observational survey of Class 0/I discs. Such hierarchical modelling of disc evolution circumvents the computational difficulty of tracing disc evolution through Class 0/I phase with direct, numerically converged simulations.
PubDate: Thu, 23 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2715
Issue No: Vol. 508, No. 2 (2021)

• Detectability of Population III stellar remnants as X-ray binaries from
tidal captures in the local Universe

Authors: Husain R; Liu B, Bromm V.
Pages: 2169 - 2178
Abstract: ABSTRACTWe assess the feasibility of detecting the compact object remnants from Population III (Pop III) stars in nearby dense star clusters, where they become luminous again as X-ray binaries (XRBs) and tidal disruption events (TDEs) via strong tidal encounters. Analytically modelling the formation of Pop III stars, coupled with a top-heavy initial mass function predicted by numerical simulations, we derive the number of (active) Pop III XRBs and TDEs in the present-day Milky Way (MW) nuclear star cluster as ${\sim} 0.06\!-\!0.3$ and ≲4 × 10−6, rendering any detection unlikely. The detection probability, however, can be significantly boosted when surveying all massive star clusters from the MW and neighbouring galaxy clusters. Specifically, we predict ∼1.5–6.5 and ∼40–2800 active Pop III XRBs in the MW and the Virgo Cluster, respectively. Our Pop III XRBs are dominated (${\sim} 99{{\ \rm per\ cent}}$) by black holes with a typical mass and luminosity of ${\sim} 45\, \rm M_{\odot }$ and ${\sim} 10^{36}\, \rm erg\, s^{-1}$. Deep surveys of nearby (${\lesssim} 30\!-\!300\, \rm Mpc$) galaxy clusters for such Pop III XRBs are well within reach of next-generation X-ray telescopes, such as Athena and Lynx.
PubDate: Fri, 24 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2744
Issue No: Vol. 508, No. 2 (2021)

• Fundamental parameters of the massive eclipsing binary HM1 8

Authors: Rodríguez C; Ferrero G, Benvenuto O, et al.
Pages: 2179 - 2193
Abstract: ABSTRACTWe present a comprehensive study of the massive binary system HM1 8, based on multi-epoch high-resolution spectroscopy, V-band photometry, and archival X-ray data. Spectra from the OWN Survey, a high-resolution optical monitoring of Southern O and WN stars, are used to analyse the spectral morphology and perform quantitative spectroscopic analysis of both stellar components. The primary and secondary components are classified as O4.5 IV(f) and O9.7 V, respectively. From a radial velocity (RV) study, we derived a set of orbital parameters for the system. We found an eccentric orbit (e = 0.14 ± 0.01) with a period of P = 5.87820 ± 0.00008 d. Through the simultaneous analysis of the RVs and the V-band light curve, we derived an orbital inclination of 70.0° ± 2.0 and stellar masses of $M_a=33.6^{+1.4}_{-1.2}~\text{M}_{\odot }$ for the primary, and $M_b=17.7^{+0.5}_{-0.7}~\text{M}_{\odot }$ for the secondary. The components show projected rotational velocities vasin i = 105 ± 14 km s−1 and vbsin i = 82 ± 15 km s−1, respectively. A tidal evolution analysis is also performed and found to be in agreement with the orbital characteristics. Finally, the available X-ray observations show no evidence of a colliding winds region; therefore, the X-ray emission is attributed to stellar winds.
PubDate: Tue, 12 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2699
Issue No: Vol. 508, No. 2 (2021)

• Charge-exchange soft X-ray emission of highly charged ions with inclusion
of multiple-electron capture

Authors: Liang G; Zhu X, Wei H, et al.
Pages: 2194 - 2203
Abstract: ABSTRACTCharge exchange has been recognized as a primary source of soft X-ray emission in many astrophysical outflow environments, including cometary and planetary exospheres impacted by the solar wind. Some models have been set up by using different data collections of charge-exchange cross-sections. However, multiple-electron transfer has not been included in these models. In this paper, we set up a charge-exchange model with the inclusion of double-electron capture (DEC), and make a detailed investigation of this process on X-ray emissions of highly charged carbon, nitrogen, oxygen, and neon ions by using available experimental cross-sections. We also study the effect of different n-selective cross-sections on soft X-ray emission by using available experimental n-distributions. This work reveals that DEC enhancement on line intensity is linearly proportional to the ratio of ion abundance in the solar wind. It is more obvious for soft X-rays from carbon ions (C4+) in collision with CO2, and the enhancement on line intensity can be up to 53 per cent with typical ion abundances [Advanced Composition Explorer (ACE)] in the solar wind. The synthetic spectra with parameters from the Ulysses mission for the solar wind reveal velocity dependence, target dependence, as well as the non-negligible contribution from the DEC.
PubDate: Mon, 13 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2537
Issue No: Vol. 508, No. 2 (2021)

• Gamma-rays and neutrinos from RX J1713–3946 in a

Authors: Cristofari P; Niro V, Gabici S.
Pages: 2204 - 2209
Abstract: ABSTRACTThe gamma-ray emission of RX J1713–3946, despite being extensively studied in the GeV and TeV domains, remains poorly understood. This is mostly because, in this range, two competing mechanisms can efficiently produce gamma-rays: the inverse Compton scattering of accelerated electrons, and interactions of accelerated protons with the nuclei of the interstellar medium (ISM). In addition to the acceleration of particles from the thermal pool, the re-acceleration of pre-existing cosmic rays is often overlooked, and has in fact also been taken into account. Especially, because of the distance to the SNR (∼1 kpc), and the low density in which the shock is currently expanding (∼10−2 cm−3), the re-acceleration of cosmic-ray electrons pre-existing in the ISM can account for a significant fraction of the observed gamma-ray emission, and contribute to the shaping of the spectrum in the GeV–TeV range. Remarkably, this emission of leptonic origin is found to be close to the level of the gamma-ray signal in the TeV range, provided that the spectrum of pre-exisiting cosmic-ray electrons is similar to that observed in the local ISM. The overall gamma-ray spectrum of RX J1713–3946 is naturally produced as the sum of leptonic emission from re-accelerated cosmic-ray electrons, and a subdominant hadronic emission from accelerated protons. We also argue that neutrino observations with next-generation detectors might lead to a detection even in the case of a lepto–hadronic origin of the gamma-ray emission.
PubDate: Tue, 12 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2380
Issue No: Vol. 508, No. 2 (2021)

• Resonant and non-resonant relaxation of globular clusters

Authors: Fouvry J; Hamilton C, Rozier S, et al.
Pages: 2210 - 2225
Abstract: ABSTRACTGlobular clusters contain a finite number of stars. As a result, they inevitably undergo secular evolution (‘relaxation’) causing their mean distribution function (DF) to evolve on long time-scales. On one hand, this long-term evolution may be interpreted as driven by the accumulation of local deflections along each star’s mean field trajectory – so-called ‘non-resonant relaxation’ (NR). On the other hand, it can be thought of as driven by non-local, collectively dressed, and resonant couplings between stellar orbits, a process termed ‘resonant relaxation’ (RR). In this paper, we consider a model globular cluster represented by a spherical, isotropic isochrone DF, and compare in detail the predictions of both RR and NR theories against tailored direct N-body simulations. In the space of orbital actions (namely the radial action and total angular momentum), we find that both RR and NR theories predict the correct morphology for the secular evolution of the cluster’s DF, although the NR theory overestimates the amplitude of the relaxation rate by a factor of ∼2. We conclude that the secular relaxation of hot isotropic spherical clusters is not dominated by collectively amplified large-scale potential fluctuations, despite the existence of a strong ℓ = 1 damped mode. Instead, collective amplification affects relaxation only marginally even on the largest scales. The predicted contributions to relaxation from smaller scale fluctuations are essentially the same from RR and NR theories.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2596
Issue No: Vol. 508, No. 2 (2021)

• The binary central star of the bipolar pre-planetary nebula
IRAS 08005−2356 (V510 Pup)

Authors: Manick R; Miszalski B, Kamath D, et al.
Pages: 2226 - 2235
Abstract: ABSTRACTCurrent models predict that binary interactions are a major ingredient in the formation of bipolar planetary nebulae (PNe) and pre-planetary nebulae (PPNe). Despite years of radial velocity (RV) monitoring, the paucity of known binaries amongst the latter systems means data are insufficient to examine this relationship in detail. In this work, we report on the discovery of a long-period (P = 2654 ± 124 d) binary at the centre of the Galactic bipolar PPN IRAS 08005−2356 (V510 Pup), determined from long-term spectroscopic and near-infrared time-series data. The spectroscopic orbit is fitted with an eccentricity of 0.36 ± 0.05, which is similar to that of other long-period post-AGB binaries. Time-resolved Hα profiles reveal high-velocity outflows (jets) with deprojected velocities up to 231$_{-27}^{+31}$ km s−1 seen at phases when the luminous primary is behind the jet. The outflow traced by Hα is likely produced via accretion on to a main-sequence companion, for which we calculate a mass of 0.63 ± 0.13 M⊙. This discovery is one of the first cases of a confirmed binary PPN and demonstrates the importance of high-resolution spectroscopic monitoring surveys using large telescopes in revealing binarity among these systems.
PubDate: Tue, 07 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2428
Issue No: Vol. 508, No. 2 (2021)

• Solar oxygen abundance

Authors: Bergemann M; Hoppe R, Semenova E, et al.
Pages: 2236 - 2253
Abstract: ABSTRACTMotivated by the controversy over the surface metallicity of the Sun, we present a re-analysis of the solar photospheric oxygen (O) abundance. New atomic models of O and Ni are used to perform non-local thermodynamic equilibrium (NLTE) calculations with 1D hydrostatic (MARCS) and 3D hydrodynamical (Stagger and Bifrost) models. The Bifrost 3D MHD simulations are used to quantify the influence of the chromosphere. We compare the 3D NLTE line profiles with new high-resolution, R$\approx 700\, 000$, spatially resolved spectra of the Sun obtained using the IAG FTS instrument. We find that the O i lines at 777 nm yield the abundance of log A(O) = 8.74 ± 0.03 dex, which depends on the choice of the H-impact collisional data and oscillator strengths. The forbidden [O i] line at 630 nm is less model dependent, as it forms nearly in LTE and is only weakly sensitive to convection. However, the oscillator strength for this transition is more uncertain than for the 777 nm lines. Modelled in 3D NLTE with the Ni i blend, the 630 nm line yields an abundance of log A(O) = 8.77 ± 0.05 dex. We compare our results with previous estimates in the literature and draw a conclusion on the most likely value of the solar photospheric O abundance, which we estimate at log A(O) = 8.75 ± 0.03 dex.
PubDate: Fri, 30 Jul 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2160
Issue No: Vol. 508, No. 2 (2021)

• Planetary nebulae with Wolf–Rayet-type central stars – II. Dissecting
the compact planetary nebula M 2-31 with GTC MEGARA

Authors: Rechy-García J; Toalá J, Cazzoli S, et al.
Pages: 2254 - 2265
Abstract: ABSTRACTWe present a comprehensive analysis of the compact planetary nebula M 2-31 investigating its spectral properties, spatio-kinematical structure, and chemical composition using Gran Telescopio Canarias (GTC) Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía (MEGARA) integral field spectroscopic observations and Nordic Optical Telescope(NOT) Alhambra Faint Object Spectrograph and Camera (ALFOSC) medium-resolution spectra and narrow-band images. The GTC MEGARA high-dispersion observations have remarkable tomographic capabilities, producing an unprecedented view of the morphology and kinematics of M 2-31 that discloses a fast spectroscopic bipolar outflow along position angles 50○ and 230○, an extended shell, and a toroidal structure or waist surrounding the central star perpendicularly aligned with the fast outflows. These observations also show that the C ii emission is confined in the central region and enclosed by the [N ii] emission. This is the first time that the spatial segregation revealed by a two-dimensional map of the C ii line implies the presence of multiple plasma components. The deep NOT ALFOSC observations allowed us to detect broad Wolf–Rayet (WR) features from the central star of M 2-31, including previously undetected broad O vi lines that suggest a reclassification as a [WO4]-type star.
PubDate: Sat, 11 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2531
Issue No: Vol. 508, No. 2 (2021)

• Cooling and instabilities in colliding flows

Authors: Markwick R; Frank A, Carroll-Nellenback J, et al.
Pages: 2266 - 2278
Abstract: ABSTRACTCollisional self-interactions occurring in protostellar jets give rise to strong shocks, the structure of which can be affected by radiative cooling within the flow. To study such colliding flows, we use the AstroBEAR AMR code to conduct hydrodynamic simulations in both one and three dimensions with a power-law cooling function. The characteristic length and time-scales for cooling are temperature dependent and thus may vary as shocked gas cools. When the cooling length decreases sufficiently and rapidly, the system becomes unstable to the radiative shock instability, which produces oscillations in the position of the shock front; these oscillations can be seen in both the one- and three-dimensional cases. Our simulations show no evidence of the density clumping characteristic of a thermal instability, even when the cooling function meets the expected criteria. In the three-dimensional case, the nonlinear thin shell instability (NTSI) is found to dominate when the cooling length is sufficiently small. When the flows are subjected to the radiative shock instability, oscillations in the size of the cooling region allow NTSI to occur at larger cooling lengths, though larger cooling lengths delay the onset of NTSI by increasing the oscillation period.
PubDate: Tue, 14 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2577
Issue No: Vol. 508, No. 2 (2021)

Authors: Cheong P; Lam A, Ng H, et al.
Pages: 2279 - 2301
Abstract: ABSTRACTWe present an update on the General-relativistic multigrid numerical (Gmunu) code, a parallelized, multidimensional curvilinear, general relativistic magnetohydrodynamics code with an efficient non-linear cell-centred multigrid elliptic solver, which is fully coupled with an efficient block-based adaptive mesh refinement module. To date, as described in this paper, Gmunu is able to solve the elliptic metric equations in the conformally flat condition approximation with the multigrid approach and the equations of ideal general-relativistic magnetohydrodynamics by means of high-resolution shock-capturing finite-volume method with reference metric formularised multidimensionally in Cartesian, cylindrical, or spherical geometries. To guarantee the absence of magnetic monopoles during the evolution, we have developed an elliptical divergence cleaning method by using the multigrid solver. In this paper, we present the methodology, full evolution equations and implementation details of Gmunu and its properties and performance in some benchmarking and challenging relativistic magnetohydrodynamics problems.
PubDate: Thu, 16 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2606
Issue No: Vol. 508, No. 2 (2021)

• Exploring the role of binarity in the origin of the bimodal rotational
velocity distribution in stellar clusters

Authors: Kamann S; Bastian N, Usher C, et al.
Pages: 2302 - 2306
Abstract: ABSTRACTMany young- and intermediate-age massive stellar clusters host bimodal distributions in the rotation rates of their stellar populations, with a dominant peak of rapidly rotating stars and a secondary peak of slow rotators. The origin of this bimodal rotational distribution is currently debated and two main theories have been put forward in the literature. The first is that all/most stars are born as rapid rotators and that interacting binaries break a fraction of the stars, resulting in two populations. The second is that the rotational distribution is a reflection of the early evolution of pre-main sequence stars, in particular, whether they are able to retain or lose their protoplanetary discs during the first few Myr. Here, we test the binary channel by exploiting multi-epoch Very Large Telescope/MUSE observations of NGC 1850, an ∼100 Myr massive cluster in the Large Magellanic Cloud, to search for differences in the binary fractions of the slow- and fast-rotating populations. If binarity is the cause of the rotational bimodality, we would expect that the slowly rotating population should have a much larger binary fraction than the rapid rotators. However, in our data we detect similar fractions of binary stars in the slow and rapidly rotating populations (5.9 ± 1.1 and 4.5 ± 0.6 per cent, respectively). Hence, we conclude that binarity is not a dominant mechanism in the formation of the observed bimodal rotational distributions.
PubDate: Thu, 16 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2643
Issue No: Vol. 508, No. 2 (2021)

• The SAMI galaxy survey: Mass and environment as independent drivers of
galaxy dynamics

Authors: van de Sande J; Croom S, Bland-Hawthorn J, et al.
Pages: 2307 - 2328
Abstract: ABSTRACTThe kinematic morphology–density relation of galaxies is normally attributed to a changing distribution of galaxy stellar masses with the local environment. However, earlier studies were largely focused on slow rotators; the dynamical properties of the overall population in relation to environment have received less attention. We use the SAMI Galaxy Survey to investigate the dynamical properties of ∼1800 early and late-type galaxies with log (M⋆/M⊙) > 9.5 as a function of mean environmental overdensity (Σ5) and their rank within a group or cluster. By classifying galaxies into fast and slow rotators, at fixed stellar mass above log (M⋆/M⊙) > 10.5, we detect a higher fraction (∼3.4σ) of slow rotators for group and cluster centrals and satellites as compared to isolated-central galaxies. We find similar results when using Σ5 as a tracer for environment. Focusing on the fast-rotator population, we also detect a significant correlation between galaxy kinematics and their stellar mass as well as the environment they are in. Specifically, by using inclination-corrected or intrinsic $\lambda _{R_{\rm {e}}}$ values, we find that, at fixed mass, satellite galaxies on average have the lowest $\lambda _{\, R_{\rm {e}},\rm {intr}}$, isolated-central galaxies have the highest $\lambda _{\, R_{\rm {e}},\rm {intr}}$, and group and cluster centrals lie in between. Similarly, galaxies in high-density environments have lower mean $\lambda _{\, R_{\rm {e}},\rm {intr}}$ values as compared to galaxies at low environmental density. However, at fixed Σ5, the mean $\lambda _{\, R_{\rm {e}},\rm {intr}}$ differences for low and high-mass galaxies are of similar magnitude as when varying Σ5 ($\Delta \lambda _{\, R_{\rm {e}},\rm {intr}} \sim 0.05$, with σrandom = 0.025, and σsyst < 0.03). Our results demonstrate that after stellar mass, environment plays a significant role in the creation of slow rotators, while for fast rotators we also detect an independent, albeit smaller, impact of mass and environment on their kinematic properties.
PubDate: Wed, 15 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2647
Issue No: Vol. 508, No. 2 (2021)

• Planet-driven density waves in protoplanetary discs: Numerical
verification of non-linear evolution theory

Authors: Cimerman N; Rafikov R.
Pages: 2329 - 2349
Abstract: ABSTRACTGravitational coupling between protoplanetary discs and planets embedded in them leads to the emergence of spiral density waves, which evolve into shocks as they propagate through the disc. We explore the performance of a semi-analytical framework for describing the non-linear evolution of the global planet-driven density waves, focusing on the low planet mass regime (below the so-called thermal mass). We show that this framework accurately captures the (quasi-)self-similar evolution of the wave properties expressed in terms of properly rescaled variables, provided that certain theoretical inputs are calibrated using numerical simulations (an approximate, first principles calculation of the wave evolution based on the inviscid Burgers equation is in qualitative agreement with simulations but overpredicts wave damping at the quantitative level). We provide fitting formulae for such inputs, in particular, the strength and global shape of the planet-driven shock accounting for non-linear effects. We use this non-linear framework to theoretically compute vortensity production in the disc by the global spiral shock and numerically verify the accuracy of this calculation. Our results can be used for interpreting observations of spiral features in discs, kinematic signatures of embedded planets in CO line emission (‘kinks’), and for understanding the emergence of planet-driven vortices in protoplanetary discs.
PubDate: Thu, 16 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2652
Issue No: Vol. 508, No. 2 (2021)

• How stars formed in warps settle into (and contaminate) thick discs

Authors: Khachaturyants T; Beraldo e Silva L, Debattista V.
Pages: 2350 - 2369
Abstract: ABSTRACTIn recent years star formation has been discovered in the Milky Way’s warp. These stars formed in the warp (warp stars) must eventually settle into the plane of the disc. We use an N-body+smooth particle hydrodynamics model of a warped galaxy to study how warp stars settle into the disc. By following warp stars in angular momentum space, we show that they first tilt to partially align with the main disc in a time-scale of ${\sim} 1\mbox{$\, {\rm Gyr}$}$. Then, once differential precession halts this process, they phase mix into an axisymmetric distribution on a time-scale of ${\sim} 6 \mbox{$\, {\rm Gyr}$}$. The warp stars end up contaminating the geometric thick disc. Because the warp in our fiducial simulation is growing, the warp stars settle to a distribution with a negative vertical age gradient as younger stars settle further from the mid-plane. While vertically extended, warp star orbits are still nearly circular and they are therefore subject to radial migration, with a net movement inwards. As a result warp stars can be found throughout the disc. The density distribution of a given population of warp stars evolves from a torus to an increasingly centrally filled-in density distribution. Therefore we argue that, in the Milky Way, warp stars should be found in the Solar Neighbourhood. Moreover, settled warp stars may constitute part of the young flaring population seen in the Milky Way’s outskirts.
PubDate: Thu, 16 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2653
Issue No: Vol. 508, No. 2 (2021)

• Revisiting the Cygnus OB associations

Authors: Quintana A; Wright N.
Pages: 2370 - 2385
Abstract: ABSTRACTOB associations play an important role in Galactic evolution, though their origins and dynamics remain poorly studied, with only a small number of systems analysed in detail. In this paper, we revisit the existence and membership of the Cygnus OB associations. We find that of the historical OB associations only Cyg OB2 and OB3 stand out as real groups. We search for new OB stars using a combination of photometry, astrometry, evolutionary models, and an SED-fitting process, identifying 4680 probable OB stars with a reliability of >90 per cent. From this sample, we search for OB associations using a new and flexible clustering technique, identifying six new OB associations. Two of these are similar to the associations Cyg OB2 and OB3, though the others bear no relationship to any existing systems. We characterize the properties of the new associations, including their velocity dispersions and total stellar masses, all of which are consistent with typical values for OB associations. We search for evidence of expansion and find that all are expanding, albeit anisotropically, with stronger and more significant expansion in the direction of Galactic longitude. We also identify two large-scale (160 pc and 25 km s−1) kinematic expansion patterns across the Cygnus region, each including three of our new associations, and attribute this to the effects of feedback from a previous generation of stars. This work highlights the need to revisit the existence and membership of the historical OB associations, if they are to be used to study their properties and dynamics.
PubDate: Thu, 16 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2663
Issue No: Vol. 508, No. 2 (2021)

• Simulating highly eccentric common envelope jet supernova impostors

Authors: Schreier R; Hillel S, Shiber S, et al.
Pages: 2386 - 2398
Abstract: ABSTRACTWe conduct three-dimensional hydrodynamical simulations of eccentric common envelope jet supernova (CEJSN) impostors, i.e. a neutron star that crosses through the envelope of a red supergiant star on a highly eccentric orbit and launches jets as it accretes mass from the envelope. Because of numerical limitations, we apply a simple prescription where we inject the assumed jets’ power into two opposite conical regions inside the envelope. We find the outflow morphology to be very complicated, clumpy, and non-spherical, having a large-scale symmetry only about the equatorial plane. The outflow morphology can substantially differ between simulations that differ by their jets’ power. We estimate by simple means the light curve to be very bumpy, to have a rise time of one to a few months, and to slowly decay in about a year to several years. These eccentric CEJSN impostors will be classified as ‘gap’ objects, i.e. having a luminosity between those of classical novae and typical supernovae (termed also ILOTs for intermediate luminosity optical transients). We strengthen a previous conclusion that CEJSN impostors might account for some peculiar ILOTs, in particular those that might repeat over time-scales of months to years.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2687
Issue No: Vol. 508, No. 2 (2021)

• Modelling spin-up episodes in accreting millisecond X-ray pulsars

Authors: Glampedakis K; Suvorov A.
Pages: 2399 - 2411
Abstract: ABSTRACTAccreting millisecond X-ray pulsars are known to provide a wealth of physical information during their successive states of outburst and quiescence. Based on the observed spin-up and spin-down rates of these objects, it is possible, among other things, to infer the stellar magnetic field strength and test models of accretion disc flow. In this paper, we consider the three accreting X-ray pulsars (XTE J1751–305, IGR J00291+5934 and SAX J1808.4–3658) with the best available timing data, and model their observed spin-up rates with the help of a collection of standard torque models that describe a magnetically threaded accretion disc truncated at the magnetospheric radius. Whilst none of these models is able to explain the observational data, we find that the inclusion of the physically motivated phenomenological parameter ξ, which controls the uncertainty in the location of the magnetospheric radius, leads to an enhanced disc-integrated accretion torque. These ‘new’ torque models are compatible with the observed spin-up rates as well as the inferred magnetic fields of these objects provided that ξ ≈ 0.1−0.5. Our results are supplemented with a discussion of the relevance of additional physics effects that include the presence of a multipolar magnetic field and general relativistic gravity.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2689
Issue No: Vol. 508, No. 2 (2021)

• Limits on long-time-scale radio transients at 150 MHz using the TGSS ADR1
and LoTSS DR2 catalogues

Authors: de Ruiter I; Leseigneur G, Rowlinson A, et al.
Pages: 2412 - 2425
Abstract: ABSTRACTWe present a search for transient radio sources on time-scales of 2–9 yr at 150 MHz. This search is conducted by comparing the first Alternative Data Release of the TIFR GMRT Sky Survey (TGSS ADR1) and the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2). The overlapping survey area covers 5570 $\rm {deg}^2$ on the sky, or 14 per cent of the total sky. We introduce a method to compare the source catalogues that involves a pair match of sources, a flux density cutoff to meet the survey completeness limit and a newly developed compactness criterion. This method is used to identify both transient candidates in the TGSS source catalogue that have no counterpart in the LoTSS catalogue and transient candidates in LoTSS without a counterpart in TGSS. We find that imaging artefacts and uncertainties and variations in the flux density scales complicate the transient search. Our method to search for transients by comparing two different surveys, while taking into account imaging artefacts around bright sources and misaligned flux scales between surveys, is universally applicable to future radio transient searches. No transient sources were identified, but we are able to place an upper limit on the transient surface density of <5.4 × 10−4 deg−2 at 150 MHz for compact sources with an integrated flux density over 100 mJy. Here we define a transient as a compact source with flux density greater than 100 mJy that appears in the catalogue of one survey without a counterpart in the other survey.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2695
Issue No: Vol. 508, No. 2 (2021)

• Non-linear resonant torus oscillations as a model of Keplerian disc warp
dynamics

Authors: Fairbairn C; Ogilvie G.
Pages: 2426 - 2446
Abstract: ABSTRACTObservations of distorted discs have highlighted the ubiquity of warps in a variety of astrophysical contexts. This has been complemented by theoretical efforts to understand the dynamics of warp evolution. Despite significant efforts to understand the dynamics of warped discs, previous work fails to address arguably the most prevalent regime – non-linear warps in Keplerian discs for which there is a resonance between the orbital, epicyclic and vertical oscillation frequencies. In this work, we implement a novel non-linear ring model, developed recently by Fairbairn and Ogilvie, as a framework for understanding such resonant warp dynamics. Here, we uncover two distinct non-linear regimes as the warp amplitude is increased. Initially, we find a smooth modulation theory that describes warp evolution in terms of the averaged Lagrangian of the oscillatory vertical motions of the disc. This hints towards the possibility of connecting previous warp theory under a generalized secular framework. Upon the warp amplitude exceeding a critical value, which scales as the square root of the aspect-ratio of our ring, the disc enters into a bouncing regime with extreme vertical compressions twice per orbit. We develop an impulsive theory that predicts special retrograde and prograde precessing warped solutions, which are identified numerically using our full equation set. Such solutions emphasize the essential activation of non-linear vertical oscillations within the disc and may have important implications for energy and warp dissipation. Future work should search for this behaviour in detailed numerical studies of the internal flow structure of warped discs.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2717
Issue No: Vol. 508, No. 2 (2021)

• Revealing the nature of the transient source MAXI J0637-430 through
spectro-temporal analysis

Authors: Baby B; Bhuvana G, Radhika D, et al.
Pages: 2447 - 2457
Abstract: ABSTRACTWe study the spectral and temporal properties of MAXI J0637-430 during its 2019–2020 outburst using Neutron Star Interior Composition Explorer (NICER), AstroSat , and Swift–XRT data. The source was in a disc dominant state within a day of its detection and traces out a ‘c’ shaped profile in the HID, similar to the ‘mini’-outbursts of the recurrent BHB 4U 1630-472. Energy spectrum is obtained in the 0.5−10 keV band with NICER and Swift–XRT, and 0.5−25 keV with AstroSat. The spectra can be modelled using a multicolour disc emission (DISKBB) convolved with a thermal Comptonization component (thcomp). The disc temperature decreases from 0.6 to 0.1 keV during the decay with a corresponding decrease in photon index (Γ) from 4.6 to 1.8. The fraction of Compton-scattered photons (fcov) remains <0.3 during the decay upto 2020 mid-January and gradually increases to 1 as the source reaches hard state. Power density spectra generated in the 0.01−100 Hz range display no quasi-periodic oscillations, although band-limited noise is seen towards the end of 2020 January. During AstroSat observations, Γ lies in the range 2.3−2.6 and rms increases from 11 to 20 per cent, suggesting that the source was in an intermediate state till 2019 November 21. Spectral fitting with the relativistic disc model (kerrbb), in conjunction with the soft-hard transition luminosity, favour a black hole with mass $3\!-\!19\, \mathrm{ M}_{\odot }$ with retrograde spin at a distance <15 kpc. Finally, we discuss the possible implications of our findings.
PubDate: Thu, 23 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2719
Issue No: Vol. 508, No. 2 (2021)

• NGC 5746: Formation history of a massive disc-dominated galaxy

Authors: Martig M; Pinna F, Falcón-Barroso J, et al.
Pages: 2458 - 2478
Abstract: ABSTRACTThe existence of massive galaxies lacking a classical bulge has often been proposed as a challenge to ΛCDM. However, recent simulations propose that a fraction of massive disc galaxies might have had very quiescent merger histories, and also that mergers do not necessarily build classical bulges. We test these ideas with deep MUSE observations of NGC 5746, a massive (∼1011 M⊙) edge-on disc galaxy with no classical bulge. We analyse its stellar kinematics and stellar populations, and infer that a massive and extended disc formed very early: 80 per cent of the galaxy’s stellar mass formed more than 10 Gyr ago. Most of the thick disc and the bar formed during that early phase. The bar drove gas towards the centre and triggered the formation of the nuclear disc followed by the growth of a boxy/peanut-shaped bulge. Around ∼8 Gyr ago, a ∼1:10 merger happened, possibly on a low-inclination orbit. The satellite did not cause significant vertical heating, did not contribute to the growth of a classical bulge, and did not destroy the bar and the nuclear disc. It was however an important event for the galaxy: by depositing its stars throughout the whole galaxy it contributed ∼30 per cent of accreted stars to the thick disc. NGC 5746 thus did not completely escape mergers, but the only relatively recent significant merger did not damage the galaxy and did not create a classical bulge. Future observations will reveal if this is representative of the formation histories of massive disc galaxies.
PubDate: Thu, 23 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2729
Issue No: Vol. 508, No. 2 (2021)

• On the road to per cent accuracy – V. The non-linear power spectrum
beyond ΛCDM with massive neutrinos and baryonic feedback

Authors: Bose B; Wright B, Cataneo M, et al.
Pages: 2479 - 2491
Abstract: ABSTRACTIn the context of forthcoming galaxy surveys, to ensure unbiased constraints on cosmology and gravity when using non-linear structure information, per cent-level accuracy is required when modelling the power spectrum. This calls for frameworks that can accurately capture the relevant physical effects, while allowing for deviations from Lambda cold dark matter (ΛCDM). Massive neutrino and baryonic physics are two of the most relevant such effects. We present an integration of the halo model reaction frameworks for massive neutrinos and beyond ΛCDM cosmologies. The integrated halo model reaction, combined with a pseudo-power spectrum modelled by HMCode2020 is then compared against N-body simulations that include both massive neutrinos and an f(R) modification to gravity. We find that the framework is 4 per cent accurate down to at least $k\approx 3 \, h\, {\rm Mpc}^{-1}$ for a modification to gravity of fR0 ≤ 10−5 and for the total neutrino mass Mν ≡ ∑mν ≤ 0.15 eV. We also find that the framework is 4 per cent consistent with EuclidEmulator2 as well as the Bacco emulator for most of the considered νwCDM cosmologies down to at least $k \approx 3 \, h$ Mpc−1. Finally, we compare against hydrodynamical simulations employing HMCode2020’s baryonic feedback modelling on top of the halo model reaction. For νΛCDM cosmologies, we find 2 per cent accuracy for Mν ≤ 0.48 eV down to at least k ≈ 5h Mpc−1. Similar accuracy is found when comparing to νwCDM hydrodynamical simulations with Mν = 0.06 eV. This offers the first non-linear, theoretically general means of accurately including massive neutrinos for beyond-ΛCDM cosmologies, and further suggests that baryonic, massive neutrino, and dark energy physics can be reliably modelled independently.
PubDate: Thu, 23 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2731
Issue No: Vol. 508, No. 2 (2021)

• Erratum: Dispersal of protoplanetary discs by the combination of
magnetically driven and photoevaporative winds

Authors: Kunitomo M; Suzuki T, Inutsuka S.
Pages: 2492 - 2492
Abstract: errata, addendaaccretion, accretion discsprotoplanetary discsstars: winds, outflows
PubDate: Tue, 12 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2748
Issue No: Vol. 508, No. 2 (2021)

• A slim disc approach to external photoevaporation of discs

Authors: Owen J; Altaf N.
Pages: 2493 - 2504
Abstract: ABSTRACTThe photoevaporation of protoplanetary discs by nearby massive stars present in their birth cluster plays a vital role in their evolution. Previous modelling assumes that the disc behaves like a classical Keplerian accretion disc out to a radius where the photoevaporative outflow is launched. There is then an abrupt change in the angular velocity profile, and the outflow is modelled by forcing the fluid parcels to conserve their specific angular momenta. Instead, we model externally photoevaporating discs using the slim disc formalism. The slim disc approach self-consistently includes the advection of radial and angular momentum as well as angular momentum redistribution by internal viscous torques. Our resulting models produce a smooth transition from a rotationally supported Keplerian disc to a photoevaporative driven outflow, where this transition typically occurs over ∼4–5 scale heights. The penetration of ultraviolet photons predominately sets the radius of the transition and the viscosity’s strength plays a minor role. By studying the entrainment of dust particles in the outflow, we find a rapid change in the dust size and surface density distribution in the transition region due to the steep gas density gradients present. This rapid change in the dust properties leaves a potentially observable signature in the continuum spectral index of the disc at mm wavelengths. Using the slim disc formalism in future evolutionary calculations will reveal how both the gas and dust evolve in their outer regions and the observable imprints of the external photoevaporation process.
PubDate: Fri, 24 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2749
Issue No: Vol. 508, No. 2 (2021)

• Comparison of the characteristics of magnetars born in death of massive
stars and merger of compact objects with swift gamma-ray burst data

Authors: Zou L; Liang E, Zhong S, et al.
Pages: 2505 - 2514
Abstract: ABSTRACTAssuming that the shallow-decaying phase in the early X-ray light curves of gamma-ray bursts (GRBs) is attributed to the dipole radiations (DRs) of a newborn magnetar, we present a comparative analysis for the magnetars born in death of massive stars and merger of compact binaries with long and short GRB (lGRB and sGRB) data observed with the Swift mission. We show that the typical braking index (n) of the magnetars is ∼3 in the sGRB sample, and it is ∼4 for the magnetars in the lGRB sample. Selecting a sub-sample of the magnetars whose spin-down is dominated by DRs (n ≲ 3) and adopting a universal radiation efficiency of 0.3, we find that the typical magnetic field strength (Bp) is 1016 G versus 1015 G and the typical initial period (P0) is ∼20 ms versus 2 ms for the magnetars in the sGRBs versus lGRBs. They follow the same relation between P0 and the isotropic GRB energy as $P_0\propto E_{\rm jet}^{-0.4}$. We also extend our comparison analysis to superluminous supernovae (SLSNe) and stable pulsars. Our results show that a magnetar born in merger of compact stars tends to have a stronger Bp and a longer P0 by about one order of magnitude than that born in collapse of massive stars. Its spin-down is dominated by the magnetic DRs as old pulsars, being due to its strong magnetic field strength, whereas the early spin-down of magnetars born in massive star collapse is governed by both the DRs and gravitational wave (GW) emission. A magnetar with a faster rotation speed should power a more energetic jet, being independent of its formation approach.
PubDate: Sat, 25 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2766
Issue No: Vol. 508, No. 2 (2021)

• Constraints on planets in nearby young moving groups detectable by
high-contrast imaging and Gaia astrometry

Authors: Wallace A; Ireland M, Federrath C.
Pages: 2515 - 2523
Abstract: ABSTRACTThe formation of giant planets can be studied through direct imaging by observing planets both during and after formation. Giant planets are expected to form either by core accretion, which is typically associated with low initial entropy (cold-start models) or by gravitational instability, associated with high initial entropy of the gas (hot-start models). Thus, constraining the initial entropy can provide insight into a planet’s formation process and determines the resultant brightness evolution. In this study, we find that, by observing planets in nearby moving groups of known age both through direct imaging and astrometry with Gaia, it will be possible to constrain the initial entropy of giant planets. We simulate a set of planetary systems in stars in nearby moving groups identified by BANYAN Σ and assume a model for planet distribution consistent with radial-velocity detections. We find that Gaia should be able to detect approximately 25 per cent of planets in nearby moving groups greater than $\sim 0.3\, M_\text{J}$. Using 5σ contrast limits of current and future instruments, we calculate the flux uncertainty, and using models for the evolution of the planet brightness, we convert this to an initial entropy uncertainty. We find that future instruments such as METIS on E-ELT as well as GRAVITY and VIKiNG with VLTI should be able to constrain the entropy to within 0.5 kB/baryon, which implies that these instruments should be able to distinguish between hot- and cold-start models.
PubDate: Mon, 27 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2769
Issue No: Vol. 508, No. 2 (2021)

• Gravitational self-lensing in populations of massive black hole binaries

Authors: Kelley L; D’Orazio D, Di Stefano R.
Pages: 2524 - 2536
Abstract: ABSTRACTThe community may be on the verge of detecting low-frequency gravitational waves from massive black hole binaries (MBHBs), but no examples of binary active galactic nuclei (AGN) have been confirmed. Because MBHBs are intrinsically rare, the most promising detection methods utilize photometric data from all-sky surveys. Gravitational self-lensing has recently been proposed as a method of detecting AGN in close separation binaries. In this study, we calculate the detectability of lensing signatures in realistic populations of simulated MBHBs. Within our model assumptions, we find that VRO’s LSST should be able to detect tens to hundreds of self-lensing binaries, with the rate uncertainty depending primarily on the orientation of AGN discs relative to their binary orbits. Roughly a quarter of lensing detectable systems should also show detectable Doppler boosting signatures. If AGN discs tend to be aligned with the orbit, lensing signatures are very nearly achromatic, while in misaligned configurations, the bluer optical bands are lensed more than redder ones. Whether substantial obscuring material (e.g. a dusty torus) will be present in close binaries remains uncertain, but our estimates suggest that a substantial fraction of systems would still be observable in this case.
PubDate: Sat, 02 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2776
Issue No: Vol. 508, No. 2 (2021)

• Testing extensions to ΛCDM on small scales with forthcoming cosmic
shear surveys

Authors: Stafford S; McCarthy I, Kwan J, et al.
Pages: 2537 - 2555
Abstract: ABSTRACTWe investigate the constraining power of forthcoming Stage-IV weak lensing surveys (Euclid, lsst, and NGRST) for extensions to the Lambda cold dark matter model on small scales, via their impact on the cosmic shear power spectrum. We use high-resolution cosmological simulations to calculate how warm dark matter (WDM), self-interacting dark matter (SIDM), and a running of the spectral index affect the non-linear matter power spectrum, P(k), as a function of scale and redshift. We evaluate the cosmological constraining power using synthetic weak lensing observations derived from these power spectra and that take into account the anticipated source densities, shape noise, and cosmic variance errors of upcoming surveys. We show that upcoming Stage-IV surveys will be able to place useful, independent constraints on both WDM models (ruling out models with a particle mass of ≲0.5 keV) and SIDM models (ruling out models with a velocity-independent cross-section of ≳10 cm2 g−1) through their effects on the small-scale cosmic shear power spectrum. Similarly, they will be able to strongly constrain cosmologies with a running spectral index. Finally, we explore the error associated with the cosmic shear cross-spectrum between tomographic bins, finding that it can be significantly affected by Poisson noise (the standard assumption is that the Poisson noise cancels between tomographic bins). We provide a new analytic form for the error on the cross-spectrum that accurately captures this effect.
PubDate: Sat, 02 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2787
Issue No: Vol. 508, No. 2 (2021)

• Large binocular telescope observations of new six compact star-forming
galaxies with [Ne v] λ3426 Å emission

Authors: Izotov Y; Thuan T, Guseva N.
Pages: 2556 - 2574
Abstract: ABSTRACTWe report the discovery of [Ne v] λ3426 emission, in addition to He ii λ4686 emission, in six compact star-forming galaxies. These observations considerably increase the sample of eight such galaxies discovered earlier by our group. For four of the new galaxies, the optical observations are supplemented by near-infrared spectra. All galaxies, but one, have H ii regions that are dense, with electron number densities of ∼ 300–700 cm−3. They are all characterized by high H β equivalent widths EW(H β) ∼ 190–520 Å and high O32 = [O iii] λ5007/[O ii] λ3727 ratios of 10–30, indicating young starburst ages and the presence of high ionization radiation. All are low-metallicity objects with 12 + logO/H = 7.46–7.88. The spectra of all galaxies show a low-intensity broad component of the H α line and five of six objects show Wolf–Rayet features. Comparison with photoionization models shows that pure stellar ionization radiation from massive stars is not hard enough to produce such strong [Ne v] and He ii emission in our galaxies. The [Ne v] λ3426/He ii λ4686 flux ratio of ∼1.2 in J1222+3602 is consistent with some contribution of active galactic nucleus ionizing radiation. However, in the remaining five galaxies, this ratio is considerably lower, $\lesssim$ 0.4. The most plausible models are likely to be non-uniform in density, where He ii and [Ne v] lines are emitted in low-density channels made by outflows and illuminated by harder ionizing radiation from radiative shocks propagating through these channels, whereas [O iii] emission originates in denser regions exposed to softer stellar ionizing sources.
PubDate: Sat, 02 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2798
Issue No: Vol. 508, No. 2 (2021)

• Using in situ solar-wind observations to generate inner-boundary
conditions to outer-heliosphere simulations – I. Dynamic time warping
applied to synthetic observations

Authors: Owens M; Nichols J.
Pages: 2575 - 2582
Abstract: ABSTRACTThe structure and dynamics of the magnetospheres of the outer planets, particularly Saturn and Jupiter, have been explored through both remote and in situ observations. Interpreting these observations often necessitates simultaneous knowledge of the solar-wind conditions impinging on the magnetosphere. Without an available upstream monitor, solar-wind context is typically provided using models initiated with either the output of magnetogram-constrained coronal models or, more commonly, in situ observations from 1 au. While 1-au observations provide a direct measure of solar-wind conditions, they are single-point observations and thus require interpolation to provide inputs to outer-heliosphere solar-wind models. In this study, we test the different interpolation methods using synthetic 1-au observations of time-evolving solar-wind structure. The simplest method is ‘corotation’, which assumes solar-wind structure is a steady state and rotates with the Sun. This method of reconstruction produces discontinuities in the solar-wind inputs as new observations become available. This can be reduced by corotating both backwards and forwards in time, but this still introduces large errors in the magnitude and timing of solar-wind streams. We show how the dynamic time warping (DTW) algorithm can provide around an order-of-magnitude improvement in solar-wind inputs to the outer-heliosphere model from in situ observations near 1 au. This is intended to build the foundation for further work demonstrating and validating methods to improve inner-boundary conditions of outer-heliosphere solar-wind models, including dealing with solar-wind transients and quantifying the improvements at Saturn and Jupiter.
PubDate: Thu, 16 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2512
Issue No: Vol. 508, No. 2 (2021)

• The young protostellar disc in IRAS 16293−2422 B is hot and shows
signatures of gravitational instability

Authors: Zamponi J; Maureira M, Zhao B, et al.
Pages: 2583 - 2599
Abstract: ABSTRACTDeeply embedded protostars are actively fed from their surrounding envelopes through their protostellar disc. The physical structure of such early discs might be different from that of more evolved sources due to the active accretion. We present 1.3 and 3 mm ALMA continuum observations at resolutions of 6.5 and 12 au, respectively, towards the Class 0 source IRAS 16293−2422 B. The resolved brightness temperatures appear remarkably high, with Tb > 100 K within ∼30 au and Tb peak over 400 K at 3 mm. Both wavelengths show a lopsided emission with a spectral index reaching values less than 2 in the central ∼20 au region. We compare these observations with a series of radiative transfer calculations and synthetic observations of magnetohydrodynamic and radiation hydrodynamic protostellar disc models formed after the collapse of a dense core. Based on our results, we argue that the gas kinematics within the disc may play a more significant role in heating the disc than the protostellar radiation. In particular, our radiation hydrodynamic simulation of disc formation, including heating sources associated with gravitational instabilities, is able to generate the temperatures necessary to explain the high fluxes observed in IRAS 16293B. Besides, the low spectral index values are naturally reproduced by the high optical depth and high inner temperatures of the protostellar disc models. The high temperatures in IRAS 16293B imply that volatile species are mostly in the gas phase, suggesting that a self-gravitating disc could be at the origin of a hot corino.
PubDate: Mon, 20 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2657
Issue No: Vol. 508, No. 2 (2021)

• Observations of compact sources in galaxy clusters using MUSTANG2

Authors: Dicker S; Battistelli E, Bhandarkar T, et al.
Pages: 2600 - 2612
Abstract: ABSTRACTCompact sources can cause scatter in the scaling relationships between the amplitude of the thermal Sunyaev–Zel’dovich Effect (tSZE) in galaxy clusters and cluster mass. Estimates of the importance of this scatter vary – largely due to limited data on sources in clusters at the frequencies at which tSZE cluster surveys operate. In this paper, we present 90 GHz compact source measurements from a sample of 30 clusters observed using the MUSTANG2 instrument on the Green Bank Telescope. We present simulations of how a source’s flux density, spectral index, and angular separation from the cluster’s centre affect the measured tSZE in clusters detected by the Atacama Cosmology Telescope (ACT). By comparing the MUSTANG2 measurements with these simulations we calibrate an empirical relationship between 1.4 GHz flux densities from radio surveys and source contamination in ACT tSZE measurements. We find 3 per cent of the ACT clusters have more than a 20 per cent decrease in Compton-y but another 3 per cent have a 10 per cent increase in the Compton-y due to the matched filters used to find clusters. As sources affect the measured tSZE signal and hence the likelihood that a cluster will be detected, testing the level of source contamination in the tSZE signal using a tSZE-selected catalogue is inherently biased. We confirm this by comparing the ACT tSZE catalogue with optically and X-ray-selected cluster catalogues. There is a strong case for a large, high-resolution survey of clusters to better characterize their source population.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2679
Issue No: Vol. 508, No. 2 (2021)

• Vibrational and rotational spectral data for possible interstellar
detection of AlH3OH2, SiH3OH, and SiH3NH2

Authors: Watrous A; Westbrook B, Davis M, et al.
Pages: 2613 - 2619
Abstract: ABSTRACTThis work provides the first full set of vibrational and rotational spectral data needed to aid in the detection of AlH3OH2, SiH3OH (silanol), and SiH3NH2 (silylamine) in astrophysical or simulated laboratory environments through the use of quantum chemical computations at the CCSD(T)-F12b level of theory employing quartic force fields for the three molecules of interest. Previous work has shown that SiH3OH and SiH3NH2 contain some of the strongest bonds of the most abundant elements in space. AlH3OH2 also contains highly abundant atoms and represents an intermediate along the reaction pathway from H2O and AlH3 to AlH2OH. All three of these molecules are also polar with AlH3OH2 having the largest dipole of 4.58 D and the other two having dipole moments in the 1.10–1.30 D range, large enough to allow for the detection of these molecules in space through rotational spectroscopy. The molecules also have substantial infrared intensities with many of the frequencies being over 90 km mol−1 and falling within the currently uncertain 12–17 μm region of observed infrared spectra. The most intense frequency for AlH3OH2 is ν9 that has an intensity of 412 km mol−1 at 777.0 cm−1 (12.87 μm). SiH3OH has an intensity of 183 km mol−1 at 1007.8 cm−1 (9.92 μm) for ν5, and SiH3NH2 has an intensity of 215 km mol−1 at 1000.0 cm−1 (10.00 μm) for ν7.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2683
Issue No: Vol. 508, No. 2 (2021)

• Identifying potential exomoon signals with convolutional neural networks

Authors: Teachey A; Kipping D.
Pages: 2620 - 2633
Abstract: ABSTRACTTargeted observations of possible exomoon host systems will remain difficult to obtain and time-consuming to analyse in the foreseeable future. As such, time-domain surveys such as Kepler, K2, and TESS will continue to play a critical role as the first step in identifying candidate exomoon systems, which may then be followed up with premier ground- or space-based telescopes. In this work, we train an ensemble of convolutional neural networks (CNNs) to identify candidate exomoon signals in single-transit events observed by Kepler. Our training set consists of ∼27 000 examples of synthetic, planet-only, and planet + moon single transits, injected into Kepler light curves. We achieve up to 88 per cent classification accuracy with individual CNN architectures and 97 per cent precision in identifying the moons in the validation set when the CNN ensemble is in total agreement. We then apply the CNN ensemble to light curves from 1880 Kepler Objects of Interest with periods >10 d (∼57 000 individual transits), and further test the accuracy of the CNN classifier by injecting planet transits into each light curve, thus quantifying the extent to which residual stellar activity may result in false positive classifications. We find a small fraction of these transits contain moon-like signals, though we caution against strong inferences of the exomoon occurrence rate from this result. We conclude by discussing some ongoing challenges to utilizing neural networks for the exomoon search.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2694
Issue No: Vol. 508, No. 2 (2021)

• Intracluster light properties in a fossil cluster at z = 0.47

Authors: Yoo J; Ko J, Kim J, et al.
Pages: 2634 - 2649
Abstract: ABSTRACTGalaxy clusters contain a diffuse stellar component outside the cluster’s galaxies, which is observed as faint intracluster light (ICL). Using Gemini/GMOS-N deep imaging and multiobject spectroscopy of a massive fossil cluster at a redshift of z = 0.47, RX J105453.3+552102 (J1054), we improve the observational constraints on the formation mechanism of the ICL. We extract the ICL surface brightness and colour profiles out to 155 kpc from the brightest cluster galaxy (BCG) with a detection limit of 28.7 mag arcsec−2 (1σ, 4.8 × 4.8arcsec2; i band). The colour of the diffuse light is similar to that of the BCG and central bright galaxies out to ∼ 70 kpc, becoming slightly bluer toward the outside. We find that the ICL distribution shows better agreement with the spatial distribution of member galaxies than with the BCG-dominated cluster luminosity distribution. We report the ICL fraction of J1054 as $15.07 \pm 4.57 {{\ \rm per\ cent}}$ in the range of 60 ∼ 155 kpc from the BCG, which appears to be higher than the ICL fraction-redshift trend in previous studies. Our findings suggest that intracluster stars seems not to be explained by one dominant production mechanism. However, a significant fraction of the ICL of J1054 may have been generated from the outskirts of infalling/satellite galaxies more recently rather than by the BCG at the early stage of the cluster.
PubDate: Tue, 21 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2707
Issue No: Vol. 508, No. 2 (2021)

• Star formation in the nearby dwarf galaxy DDO 53: interplay between gas
accretion and stellar feedback

Authors: Egorov O; Lozinskaya T, Vasiliev K, et al.
Pages: 2650 - 2667
Abstract: ABSTRACTWe present the results of a multiwavelength study of the nearby dwarf galaxy DDO 53 – a relatively isolated member of the M 81 group. We analyse the atomic and ionized gas kinematics (based on the observations with Fabry–Perot interferometer in H α line and archival data in H i 21 cm line), distribution, excitation, and oxygen abundance of the ionized gas (based on the long-slit and integral-field spectroscopy and on imaging with narrow-band filters), and their relation with the young massive stars (based on archival HST data). We detect a faint 2-kpc sized supershell of ionized gas surrounding the galaxy. Most probably, this structure represents a large-scale gas outflow, however, it could be also created by the ionizing quanta leaking from star-forming regions to the marginally detected atomic hydrogen surrounding the galactic disc. We analyse the properties of the anomalous H i in the north part of the galaxy and find that its peculiar kinematics is also traced by ionized gas. We argue that this H i feature is related to the accreting gas cloud captured from the intergalactic medium or remaining after the merger event occurred >1 Gyr ago. The infalling gas produces shocks in the interstellar medium and could support the star formation activity in the brightest region in DDO 53.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2710
Issue No: Vol. 508, No. 2 (2021)

• Physical conditions and chemical abundances in PN M 2-36. Results from
deep echelle observations

Authors: Espíritu J; Peimbert A.
Pages: 2668 - 2687
Abstract: ABSTRACTWe present a spectrum of the planetary nebula (PN) M 2-36 obtained using the Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large Telescope. 446 emission lines are detected. We perform an analysis of the chemical composition using multiple electron temperature (Te) and density (ne) diagnostics. Te and ne are computed using a variety of methods, including collisionally excited line (CEL) ratios, O++ optical recombination lines (ORLs), and measuring the intensity of the Balmer jump. Besides the classical CEL abundances, we also present robust ionic abundances from ORLs of heavy elements. From CELs and ORLs of O++, we obtain a new value for the Abundance Discrepancy Factor (ADF) of this nebula, being ADF(O++) = 6.76 ± 0.50. From all the different line ratios that we study, we find that the object cannot be chemically homogeneous; moreover, we find that two-phased photoionization models are unable to simultaneously reproduce critical ${\rm O\, \small {II}}$ and [${\rm O\, \small {III}}$] line ratios. However, we find a three-phased model able to adequately reproduce such ratios. While we consider this to be a toy model, it is able to reproduce the observed temperature and density line diagnostics. Our analysis shows that it is important to study high ADF PNe with high spectral resolution, since its physical and chemical structure may be more complicated than previously thought.
PubDate: Mon, 27 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2746
Issue No: Vol. 508, No. 2 (2021)

• Isochrone fitting of Galactic globular clusters – III. NGC 288,
NGC 362, and NGC 6218 (M12)

Authors: Gontcharov G; Khovritchev M, Mosenkov A, et al.
Pages: 2688 - 2705
Abstract: ABSTRACTWe present new isochrone fits to colour–magnitude diagrams of the Galactic globular clusters NGC 288, NGC 362, and NGC 6218 (M12). We utilize a lot of photometric bands from the ultraviolet to mid-infrared by use of data from the HST, Gaia, unWISE, Pan-STARRS, and other photometric sources. In our isochrone fitting, we use theoretical models and isochrones from the Dartmouth Stellar Evolution Program and Bag of Stellar Tracks and Isochrones for α-enhanced abundance [α/Fe] = +0.40, different helium abundances, and a metallicity of about [Fe/H] = −1.3 adopted from the literature. We derive the most probable distances 8.96 ± 0.05, 8.98 ± 0.06, and 5.04 ± 0.05 kpc, ages 13.5 ± 1.1, 11.0 ± 0.6, and 13.8 ± 1.1 Gyr, extinctions AV = 0.08 ± 0.03, 0.11 ± 0.04, and 0.63 ± 0.03 mag, and reddenings E(B − V) = 0.014 ± 0.010, 0.028 ± 0.011, and 0.189 ± 0.010 mag for NGC 288, NGC 362, and NGC 6218, respectively. The distance estimates from the different models are consistent, while those of age, extinction, and reddening are not. The uncertainties of age, extinction, and reddening are dominated by some intrinsic systematic differences between the models. However, the models agree in their relative age estimates: NGC 362 is 2.6 ± 0.5 Gyr younger than NGC 288 and 2.8 ± 0.5 Gyr younger than NGC 6218, confirming age as the second parameter for these clusters. We provide reliable lists of the cluster members and precise cluster proper motions from the Gaia Early Data Release 3.
PubDate: Sat, 25 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2756
Issue No: Vol. 508, No. 2 (2021)

• Semi-analytic forecasts for JWST – V. AGN luminosity functions and
helium reionization at z = 2–7

Authors: Yung L; Somerville R, Finkelstein S, et al.
Pages: 2706 - 2729
Abstract: ABSTRACTActive galactic nuclei (AGN) forming in the early universe are thought to be the primary source of hard ionizing photons contributing to the reionization of intergalactic helium. However, the number density and spectral properties of high-redshift AGN remain largely unconstrained. In this work, we make use of physically informed models calibrated with a wide variety of available observations to provide estimates for the role of AGN throughout the Epoch of Reionization. We present AGN luminosity functions in various bands between z = 2 and 7 predicted by the well-established Santa Cruz semi-analytic model, which includes modelling of black hole accretion and AGN feedback. We then combine the predicted AGN populations with a physical spectral model for self-consistent estimates of ionizing photon production rates, which depend on the mass and accretion rate of the accreting supermassive black hole. We then couple the predicted comoving ionizing emissivity with an analytic model to compute the subsequent reionization history of intergalactic helium and hydrogen. This work demonstrates the potential of coupling physically motivated analytic or semi-analytic techniques to capture multiscale physical processes across a vast range of scales (here, from AGN accretion discs to cosmological scales). Our physical model predicts an intrinsic ionizing photon budget well above many of the estimates in the literature, meaning that helium reionization can comfortably be accomplished even with a relatively low escape fraction. We also make predictions for the AGN populations that are expected to be detected in future James Webb Space Telescope surveys.
PubDate: Sat, 25 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2761
Issue No: Vol. 508, No. 2 (2021)

• A joint occultation and speckle investigation of the binary star TYC
1947-290-1 and of the asteroid (87) Sylvia

Authors: Dyachenko V; Richichi A, Obolentseva M, et al.
Pages: 2730 - 2735
Abstract: ABSTRACTWe report on the occultation of the star TYC 1947-290-1 by the asteroid (87) Sylvia. While asteroidal occultations occurring at fixed professional-level locations are relatively rare and are only recently starting to be observed with sufficiently high time resolution and sensitivity, they have the capability to measure sub-milliarcsecond angular diameters. The event described here was especially outstanding because the star was revealed to be a small-separation binary (≈10 mas at discovery), while at the same time the asteroid is not only one of the largest in size but it also has two satellite moons. The observations were carried out at the Russian 6-m telescope in 2019 December, and initially consisted of both a fast photometric series of the occultation itself, as well as of extensive speckle interferometry of the star and asteroid in the time immediately before and after the occultation. Subsequently, we obtained speckle data of TYC 1947-290-1 over a period of 1 yr after the event. We are able to present a detailed study of the binary star including measurements of the angular diameter of the stellar components, their geometry, and relative fluxes over several bandpasses, and to provide an accurate determination of the size of (87) Sylvia. We emphasize that we have been able to obtain the smallest ever directly measured stellar diameter, below the 100 micro-arcsecond level. Our data are also suitable for imaging of the asteroid by speckle holography, a task which we intend to carry out in a separate work.
PubDate: Sat, 25 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2767
Issue No: Vol. 508, No. 2 (2021)

• A systematic bias in fitting the surface-density profiles of interstellar
filaments

Authors: Whitworth A; Priestley F, Arzoumanian D.
Pages: 2736 - 2742
Abstract: ABSTRACTThe surface-density profiles (SDPs) of dense filaments, in particular those traced by dust emission, appear to be well fit with Plummer profiles, i.e. Σ(b) = ΣB + ΣO{1 + [b/wO]2}[1 − p]/2. Here, $\, \Sigma _{{\rm B}}$ is the background surface density;  ΣB + ΣO is the surface density on the filament spine;  b is the impact parameter of the line-of-sight relative to the filament spine;  wO is the Plummer scale-length (which for fixed p is exactly proportional to the full width at half-maximum, $w_{{\rm O}}=\rm{\small fwhm}/2\lbrace 2^{2/[p-1]}-1\rbrace ^{1/2}$); and $\, p$ is the Plummer exponent (which reflects the slope of the SDP away from the spine). In order to improve signal to noise, it is standard practice to average the observed surface densities along a section of the filament, or even along its whole length, before fitting the profile. We show that, if filaments do indeed have intrinsic Plummer profiles with exponent pINTRINSIC, but there is a range of wO values along the length of the filament (and secondarily a range of ΣB values), the value of the Plummer exponent, pFIT, estimated by fitting the averaged profile, may be significantly less than pINTRINSIC. The decrease, Δp = pINTRINSIC − pFIT, increases monotonically (i) with increasing pINTRINSIC; (ii) with increasing range of wO values; and (iii) if (but only if) there is a finite range of wO values, with increasing range of ΣB values. For typical filament parameters, the decrease is insignificant if pINTRINSIC = 2 (0.05 ≲ Δp ≲ 0.10), but for pINTRINSIC = 3, it is larger (0.18 ≲ Δp ≲ 0.50), and for pINTRINSIC = 4, it is substantial (0.50 ≲ Δp ≲ 1.15). On its own, this effect is probably insufficient to support a value of pINTRINSIC much greater than pFIT ≃ 2, but it could be important in combination with other effects.
PubDate: Fri, 01 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2782
Issue No: Vol. 508, No. 2 (2021)

• Dust traffic jams in inclined circumbinary protoplanetary discs – I.
Morphology and formation theory

Authors: Aly H; Gonzalez J, Nealon R, et al.
Pages: 2743 - 2757
Abstract: ABSTRACTGas and dust in inclined orbits around binaries experience precession induced by the binary gravitational torque. The difference in precession between gas and dust alters the radial drift of weakly coupled dust and leads to density enhancements where the radial drift is minimized. We explore this phenomenon using 3D hydrodynamical simulations to investigate the prominence of these ‘dust traffic jams’ and the evolution of the resulting dust sub-structures at different disc inclinations and binary eccentricities. We then derive evolution equations for the angular momentum of warped dust discs and implement them in a 1D code and present calculations to further explain these traffic jams. We find that dust traffic jams in inclined circumbinary discs provide significant dust density enhancements that are long lived and can have important consequences for planetesimal formation.
PubDate: Sat, 02 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2794
Issue No: Vol. 508, No. 2 (2021)

• Measuring cosmic density of neutral hydrogen via stacking the DINGO-VLA
data

Authors: Chen Q; Meyer M, Popping A, et al.
Pages: 2758 - 2770
Abstract: ABSTRACTWe use the 21-cm emission-line data from the Deep Investigation of Neutral Gas Origin-Very Large Array (DINGO-VLA) project to study the atomic hydrogen gas H i of the Universe at redshifts z < 0.1. Results are obtained using a stacking analysis, combining the H i signals from 3622 galaxies extracted from 267 VLA pointings in the G09 field of the Galaxy and Mass Assembly Survey (GAMA). Rather than using a traditional one-dimensional spectral stacking method, a three-dimensional cubelet stacking method is used to enable deconvolution and the accurate recovery of average galaxy fluxes from this high-resolution interferometric data set. By probing down to galactic scales, this experiment also overcomes confusion corrections that have been necessary to include in previous single-dish studies. After stacking and deconvolution, we obtain a 30σ H i mass measurement from the stacked spectrum, indicating an average H i mass of ${\rm{M_{\rm{{H}\,\small{I}}}}}=(1.67\pm 0.18)\times 10^{9}~{\rm{{\rm M}_{\odot }}}$. The corresponding cosmic density of neutral atomic hydrogen is ${\rm{\Omega _{\rm{{H}\,\small{I}}}}}=(0.38\pm 0.04)\times 10^{-3}$ at redshift of z = 0.051. These values are in good agreement with earlier results, implying there is no significant evolution of $\Omega _{\rm{{H}\,\small{I}}}$ at lower redshifts.
PubDate: Sat, 02 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2810
Issue No: Vol. 508, No. 2 (2021)

• On the impact of the numerical method on magnetic reconnection and
particle acceleration – I. The MHD case

Authors: Puzzoni E; Mignone A, Bodo G.
Pages: 2771 - 2783
Abstract: ABSTRACTWe present 2D magnetohydrodynamics numerical simulations of tearing-unstable current sheets coupled to a population of non-thermal test particles, in order to address the problem of numerical convergence with respect to grid resolution, numerical method, and physical resistivity. Numerical simulations are performed with the pluto code for astrophysical fluid dynamics through different combinations of Riemann solvers, reconstruction methods, and grid resolutions at various Lundquist numbers. The constrained transport method is employed to control the divergence-free condition of magnetic field. Our results indicate that the reconnection rate of the background tearing-unstable plasma converges only for finite values of the Lundquist number and for sufficiently large grid resolutions. In general, it is found that (for a second-order scheme) the minimum threshold for numerical convergence during the linear phases requires the number of computational zones covering the initial current sheet width to scale roughly as $\sim \sqrt{\bar{S}}$, where $\bar{S}$ is the Lundquist number defined on the current sheet width. On the other hand, the process of particle acceleration is found to be nearly independent of the underlying numerical details inasmuch as the system becomes tearing-unstable and enters in its non-linear stages. In the limit of large $\bar{S}$, the ensuing power-law index quickly converge to p ≈ 1.7, consistently with the fast reconnection regime.
PubDate: Sat, 02 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2813
Issue No: Vol. 508, No. 2 (2021)

• The high-redshift tail of stellar reionization in LCDM is beyond the reach
of the low-ℓ CMB

Authors: Wu X; McQuinn M, Eisenstein D, et al.
Pages: 2784 - 2797
Abstract: ABSTRACTThe first generation (Pop-III) stars can ionize 1–10 per cent of the universe by z = 15, when the metal-enriched (Pop-II) stars may contribute negligibly to the ionization. This low ionization tail might leave detectable imprints on the large-scale CMB E-mode polarization. However, we show that physical models for reionization are unlikely to be sufficiently extended to detect any parameter beyond the total optical depth through reionization. This result is driven in part by the total optical depth inferred by Planck, indicating a reionization midpoint around z = 8, which in combination with the requirement that reionization completes by z ≈ 5.5 limits the amplitude of an extended tail. To demonstrate this, we perform semi-analytic calculations of reionization including Pop-III star formation in minihalos with Lyman-Werner feedback. We find that standard Pop-III models need to produce very extended reionization at z > 15 to be distinguishable at 2-σ from Pop-II-only models, assuming a cosmic variance-limited measurement of the low-ℓ EE power spectrum. However, we show that unless there is a late-time quenching mechanism such as from strong X-ray feedback or some other extreme Pop-III scenario, structure formation makes it quite challenging to produce high enough Thomson scattering optical depth from z > 15, τ(z > 15), and still be consistent with other observational constraints on reionization.
PubDate: Sat, 02 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2815
Issue No: Vol. 508, No. 2 (2021)

• High-redshift quasars at z ≥ 3 – I. Radio spectra

Authors: Sotnikova Y; Mikhailov A, Mufakharov T, et al.
Pages: 2798 - 2814
PubDate: Thu, 14 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2114
Issue No: Vol. 508, No. 2 (2021)

• Investigation of the properties of four rotating radio transients at
111 MHz

Authors: Tyul’bashev S; Smirnova T, Brylyakova E, et al.
Pages: 2815 - 2822
Abstract: ABSTRACTWe present an analysis of the individual pulses of four rotating radio transients (RRATs), previously discovered in a monitoring survey running for 5.5 yr at the frequency of 111 MHz. At a time interval equivalent to 5 d of continuous observations for each RRAT, 90, 389, 206 and 157 pulses were detected in J0640+07, J1005+30, J1132+25 and J1336+33, respectively. The investigated RRATs have different distributions of their pulse amplitudes. For J0640+07 and J1132+25, the distribution is described by a single exponent over the entire range of flux densities. For J1005+30 and J1336+33, it is a lognormal function with a power-law tail. For J0640+07 and J1005+30, we have detected pulses with a signal-to-noise ratio (S/N) of a few hundred. For J1132+25 and J1336+33, the S/N of the strongest pulses reaches several tens. These RRATs show a strong change in their emission. When the strengths of their pulse amplitudes are significantly changed, we see long intervals of absence of emission or its strong attenuation. The analysis carried out in this work shows that it is possible that all the studied RRATs are, apparently, pulsars with giant pulses.
PubDate: Thu, 14 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2612
Issue No: Vol. 508, No. 2 (2021)

• A deep search for faint Chandra X-ray sources, radio sources, and optical
counterparts in NGC 6752

Authors: Cohn H; Lugger P, Zhao Y, et al.
Pages: 2823 - 2847
Abstract: ABSTRACTWe report the results of a deep search for faint Chandra X-ray sources, radio sources, and optical counterparts in the nearby, core-collapsed globular cluster, NGC 6752. We combined new and archival Chandra imaging to detect 51 X-ray sources (12 of which are new) within the 1.9 arcmin half-light radius. Three radio sources in deep ATCA 5 and 9 GHz radio images match with Chandra sources. We have searched for optical identifications for the expanded Chandra source list using deep Hubble Space Telescope photometry in B435, R625, H α, UV275, and U336. Among the entire sample of 51 Chandra sources, we identify 18 cataclysmic variables (CVs), 9 chromospherically active binaries (ABs), 3 red giants (RGs), 3 galaxies (GLXs), and 6 active galactic nuclei (AGNs). Three of the sources are associated with millisecond pulsars (MSPs). As in our previous study of NGC 6752, we find that the brightest CVs appear to be more centrally concentrated than the faintest CVs, although the effect is no longer statistically significant as a consequence of the inclusion in the faint group of two intermediate brightness CVs. This possible difference in the radial distributions of the bright and faint CV groups appears to indicate that mass segregation has separated them. We note that photometric incompleteness in the crowded central region of the cluster may also play a role. Both groups of CVs have an inferred mass above that of the main-sequence turnoff stars. We discuss the implications for the masses of the CV components.
PubDate: Mon, 27 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2636
Issue No: Vol. 508, No. 2 (2021)

• Observational constraints on Tsallis modified gravity

Authors: Asghari M; Sheykhi A.
Pages: 2855 - 2861
Abstract: ABSTRACTThe thermodynamics-gravity conjecture reveals that one can derive the gravitational field equations by using the first law of thermodynamics and vice versa. Considering the entropy associated with the horizon in the form of non-extensive Tsallis entropy, S ∼ Aβ here, we first derive the corresponding gravitational field equations by applying the Clausius relation δQ = TδS to the horizon. We then construct the Friedmann equations of Friedmann-Lemaître-Robertson-Walker Universe based on Tsallis modified gravity (TMG). Moreover, in order to constrain the cosmological parameters of TMG model, we use observational data, including Planck cosmic microwave background, weak lensing, supernovae, baryon acoustic oscillations, and redshift-space distortions data. Numerical results indicate that TMG model with a quintessential dark energy is more compatible with the low redshift measurements of large scale structures by predicting a lower value for the structure growth parameter σ8 with respect to ΛCDM model. This implies that TMG model would slightly alleviate the σ8 tension.
PubDate: Mon, 20 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2671
Issue No: Vol. 508, No. 2 (2021)

• A 15.5 GHz detection of the galaxy cluster minihalo in
RXJ1720.1+2638

Authors: Perrott Y; Carvalho P, Elwood P, et al.
Pages: 2862 - 2880
Abstract: ABSTRACTRXJ1720.1+2638 is a cool-core, ‘relaxed-appearing’ cluster with a minihalo previously detected up to 8.4 GHz, confined by X-ray-detected cold fronts. We present observations of the minihalo at 13–18 GHz with the Arcminute Microkelvin Imager telescope, simultaneously modelling the Sunyaev–Zel’dovich signal of the cluster in conjunction with Planck and Chandra data in order to disentangle the non-thermal emission of the minihalo. We show that the previously reported steepening of the minihalo emission at 8.4 GHz is not supported by the AMI data and that the spectrum is consistent with a single power law up to 18 GHz. We also show the presence of a larger scale component of the minihalo extending beyond the cold fronts. Both of these observations could be explained by the ‘hadronic’ or ‘secondary’ mechanism for the production of relativistic electrons, rather than the currently favoured ‘re-acceleration’ mechanism and/or multiple episodes of jet activity from the active galactic nucleus in the brightest cluster galaxy.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2706
Issue No: Vol. 508, No. 2 (2021)

• Investigating the evolution of PKS B1144−379: comparison of VLBI and
scintillation techniques

Authors: Said N; Ellingsen S, Shabala S, et al.
Pages: 2881 - 2896
Abstract: ABSTRACTWe have investigated the evolution of the BL Lac object PKS B1144−379 using the University of Tasmania Ceduna 30-m radio telescope at a frequency of 6.7 GHz and very long baseline interferometry (VLBI) data at 8.6 GHz. Variability time-scales associated with two flares detected in 2005 November and 2008 August were derived from long-term variations in total flux density monitored by Ceduna between 2003 and 2011. A kinematic study of the parsec-scale jet of PKS B1144−379 was performed using VLBI data obtained between 1997 and 2018. Quasi-periodic flarings with a period of ∼3–4 yr were observed. Over the 20-yr interval, the average jet position angle was found to be ~150°.
PubDate: Wed, 22 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2724
Issue No: Vol. 508, No. 2 (2021)

• 1/f noise analysis for FAST H i intensity mapping drift-scan
experiment

Authors: Hu W; Li Y, Wang Y, et al.
Pages: 2897 - 2909
Abstract: ABSTRACTWe investigate the 1/f noise of the Five-hundred-meter Aperture Spherical Telescope (FAST) receiver system using drift-scan data from an intensity mapping pilot survey. All the 19 beams have 1/f fluctuations with similar structures. Both the temporal and the 2D power spectrum densities are estimated. The correlations directly seen in the time series data at low frequency f are associated with the sky signal, perhaps due to a coupling between the foreground and the system response. We use singular value decomposition (SVD) to subtract the foreground. By removing the strongest components, the measured 1/f noise power can be reduced significantly. With 20 modes subtraction, the knee frequency of the 1/f noise in a 10-MHz band is reduced to $1.8 \times 10^{-3}\, {\rm Hz}$, well below the thermal noise over 500-s time-scale. The 2D power spectra show that the 1/f-type variations are restricted to a small region in the time-frequency space and the correlations in frequency can be suppressed with SVD modes subtraction. The residual 1/f noise after the SVD mode subtraction is uncorrelated in frequency, and a simple noise diode frequency-independent calibration of the receiver gain at 8-s interval does not affect the results. The 1/f noise can be important for H i intensity mapping, we estimate that the 1/f noise has a knee frequency (fk) ∼ 6 × 10−4 Hz, and time and frequency correlation spectral indices (α) ∼ 0.65, (β) ∼ 0.8 after the SVD subtraction of 30 modes. This can bias the H i power spectrum measurement by 10 per cent.
PubDate: Sat, 02 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2728
Issue No: Vol. 508, No. 2 (2021)

• Revealing the unusual structure of the KAT-7-discovered giant radio galaxy
J0133−1302

Authors: Mhlahlo N; Jamrozy M.
Pages: 2910 - 2922
Abstract: ABSTRACTWe present a new study of the 1.7 Mpc KAT-7-discovered Giant Radio Galaxy, J0133−1302, which was carried out using GMRT data at 323 and 608 MHz. This source is located at RA 01h33m13s and Dec. −13○03′00″ and has a photometric redshift of ∼0.3. We discovered unusual morphological properties of the source which include lobes that are exceptionally asymmetric, where the upper lobe is much further from the core when compared to the lower lobe, and a complex structure of the upper lobe. The complex structure of the upper lobe hints at the presence of another source, in close proximity to the edge of the lobe, which resembles a bent-double, or distorted bent tail Radio Galaxy. Both the upper lobe and the lower lobe have a steep spectrum, and the synchrotron age of the lower lobe should be less than about 44 Myr. The core has an inverted spectrum, and our results suggest that the parent Galaxy in J0133−1302 is starting a new jet activity. Our spectral analysis indicates that this source could be a GigaHertz Peaked Spectrum radio Galaxy.
PubDate: Thu, 23 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2732
Issue No: Vol. 508, No. 2 (2021)

• globalemu: a novel and robust approach for emulating the sky-averaged
21-cm signal from the cosmic dawn and epoch of reionization

Authors: Bevins H; Handley W, Fialkov A, et al.
Pages: 2923 - 2936
Abstract: ABSTRACTEmulation of the Global (sky-averaged) 21-cm signal with neural networks has been shown to be an essential tool for physical signal modelling. In this paper, we present globalemu, a Global 21-cm signal emulator that uses redshift as a character-defining variable alongside a set of astrophysical parameters to estimate the signal brightness temperature. Combined with physically motivated data pre-processing, this makes for a reliable and fast emulator that is relatively insensitive to the network design. globalemu can emulate a high-resolution signal in 1.3 ms in comparison to 133 ms, a factor of 102 improvement, when using the existing public state-of-the-art 21cmGEM. We illustrate, with the standard astrophysical models used to train 21cmGEM, that globalemu is almost twice as accurate and for a test set of ≈1700 signals we achieve a mean root mean squared error of 2.52 mK across the band z = 7–28 [≈10 per cent the expected noise of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH)]. The models are parametrized by the star formation efficiency, f*, minimum virial circular velocity, Vc, X-ray efficiency, fX, cosmic microwave background optical depth, τ, the slope and low energy cut-off of the X-ray spectral energy density, α and νmin, respectively, and the mean free path of ionizing photons, Rmfp. globalemu provides a flexible framework for easily emulating updated simulations of the Global signal and in addition the neutral fraction history. The emulator is pip installable and available at https://github.com/htjb/globalemu. globalemu will be used extensively by the REACH collaboration.
PubDate: Sat, 25 Sep 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2737
Issue No: Vol. 508, No. 2 (2021)

• Periodic variability of the z = 2.0 quasar QSO B1312+7837

Authors: Minev M; Ivanov V, Trifonov T, et al.
Pages: 2937 - 2943
Abstract: ABSTRACTWe report here the first results from a 15-yr long variability monitoring of the z = 2.0 quasar QSO B1312+7837. It shows luminosity changes with a period P ∼ 6.13 yr (P ∼ 2.04 yr at rest frame) and amplitude of ∼0.2 mag, superimposed on a gradual dimming at a rate of ∼0.55 mag per 100 yr. Two false periods associated with power peaks in the data windowing function were discarded. The measured period is confirmed with a bootstrapping Monte Carlo simulation. A damped random walk model yields a better fit to the data than a sine-function model, but at the cost of employing some high-frequency variations which are typically not seen in quasars. We consider the possible mechanisms driving this variability, and conclude that orbital motion of two supermassive black holes – result from a recent galaxy merger – is a possible explanation.
PubDate: Fri, 01 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2763
Issue No: Vol. 508, No. 2 (2021)

• Erratum: The tidal evolution of dark matter substructure – II. The
impact of artificial disruption on subhalo mass functions and radial
profiles

Authors: Green S; van den Bosch F, Jiang F.
Pages: 2944 - 2945
Abstract: errata, addendamethods: numericalgalaxies: haloesdark matter
PubDate: Thu, 14 Oct 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab2786
Issue No: Vol. 508, No. 2 (2021)

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