119240757
BSG alignment of SDSS galaxy groups
We study the alignment signal between the distribution of brightest satellite galaxies (BSGs) and the major axis of their host groups using SDSS group catalog constructed by Yang et al. (2007). After correcting for the effect of group ellipticity, a statistically significant (∼ 5σ) major-axis alignment is detected and the alignment angle is found to be 43.0 ± 0.4. More massive and richer groups show stronger BSG alignment. The BSG alignment around blue BCGs is slightly stronger than that around red BCGs. And red BSGs have much stronger major-axis alignment than blue BSGs. Unlike BSGs, other satellites do not show very significant alignment with group major axis. We further explore the BSG alignment in semi-analytic model (SAM) constructed by Guo et al. (2011). We found general good agreement with observations: BSGs in SAM show strong major-axis alignment which depends on group mass and richness in the same way as observations; and none of other satellites exhibit prominent alignment. However, discrepancy also exists in that the SAM shows opposite BSG color dependence, which is most probably induced by the missing of large scale environment ingredient in SAM. The combination of two popular scenarios can explain the detected BSG alignment. The first one: satellites merged into the group preferentially along the surrounding filaments, which is strongly aligned with the major axis of the group. The second one: BSGs enter their host group more recently than other satellites, then will preserve more information about the assembling history and so the major-axis alignment. In SAM, we found positive evidence for the second scenario by the fact that BSGs merged into groups statistically more recently than other satellites. We also found that most of BSGs (80%) were BCGs before they merged into groups and earlier merged BSGs tend to be closer to their BCGs than other BSGs. On the other hand, although is opposite in SAM, the BSG color dependence in observation might indicate the first scenario as well. Subject headings: BSG – alignment – group of galaxies – SAM – SDSS
5659355
SYSTEMATIC ERRORS IN THE DETERMINATION OF HUBBLE CONSTANT DUE TO THE ASPHERICITY AND NONISOTHERMALITY OF CLUSTERS OF GALAXIES
We present statistical studies on the systematic errors in the determination of the Hubble constant H0 from joint analyses of X-ray and the Sunyaev-Zel'dovich (SZ) effect of clusters of galaxies. We focus on the effects of their triaxiality and nonisothermality. From the triaxial model of dark matter halos obtained from numerical simulations, we derive the distribution of the intracluster gas under the assumption of the hydrodynamic equilibrium. Both the isothermal and the polytropic gases are investigated. We run Monte Carlo simulations to generate samples of clusters according to the distributions of their masses, axial ratios, concentration parameters, and line-of-sight directions. The estimation of H0 is done by fitting X-ray and SZ profiles of a triaxial cluster with the isothermal and spherical β model. We find that for a sample of clusters with M = 1014 h-1 M☉ and z = 0.1, the estimated H0 is positively biased with H(estimated) ≈ 1.05H0(true) and H(estimated) ≈ 1.05H0(true) for the isothermal case. For the polytropic case with γ = 1.15, the bias is large with H(estimated) ≈ 1.35H0(true) and H(estimated) ≈ 3H0(true). For a mass-limited sample of clusters with Mlim = 1013 h-1 M☉, the results are similar. On the other hand, such a large overestimation has not been seen in real observations. It is noticed that the β-value for observed clusters is within the range of 0.5-0.8. Considering only the subsample in Monte Carlo simulations with β in the range of 0.5-0.8, we have H(estimated) = 1.002H0(true) and H(estimated) = 0.994H0(true) for the isothermal and polytropic cases, respectively. We further find that the value of β is more sensitive to the intrinsic asphericity of clusters than the axial ratio of two-dimensional X-ray images η is. Limiting to clusters with β ≥ 0.5 essentially excludes highly aspherical clusters from the sample. From this subsample of clusters, we can get a fair estimate on H0.
119263928
Made-to-measure galaxy models – III. Modelling with Milky Way observations
We demonstrate how the Syer and Tremaine made-to-measure method of stellar dynamical modelling can be adapted to model a rotating galactic bar. We validate our made-to-measure changes using observations constructed from the existing Shen et al. N-body model of the Milky Way bar, together with kinematic observations of the Milky Way bulge and bar taken by the Bulge Radial Velocity Assay. Our results for a combined determination of the bar angle and bar pattern speed (approximate to 30 degrees and approximate to 40 km s(-1) kpc(-1)) are consistent with those determined by the N-body model. Whilst the made-to-measure techniques we have developed are applied using a particular N-body model and observational data set, they are in fact general and could be applied to other Milky Way modelling scenarios utilizing different N-body models and data sets. Additionally, we use the exercise as a vehicle for illustrating how N-body and made-to-measure methods might be combined into a more effective method.
13558011
The Bulge Radial Velocity Assay (BRAVA). II. Complete Sample And Data Release
We present new radial velocity measurements from the Bulge Radial Velocity Assay, a large-scale spectroscopic survey of M-type giants in the Galactic bulge/bar region. The sample of ~4500 new radial velocities, mostly in the region –10° < l < +10° and b ≈ –6°, more than doubles the existent published data set. Our new data extend our rotation curve and velocity dispersion profile to +20°, which is ~2.8 kpc from the Galactic center. The new data confirm the cylindrical rotation observed at –6° and –8° and are an excellent fit to the Shen et al. N-body bar model. We measure the strength of the TiOe molecular band as a first step toward a metallicity ranking of the stellar sample, from which we confirm the presence of a vertical abundance gradient. Our survey finds no strong evidence of previously unknown kinematic streams. We also publish our complete catalog of radial velocities, photometry, TiO band strengths, and spectra, which is available at the Infrared Science Archive as well as at UCLA.
5692175
Effects of correlation between merging steps on the global halo formation
The excursion set theory of halo formation is modified by adopting the fractional Brownian motion, to account for possible correlation between merging steps. We worked out analytically the conditional mass function, halo merging rate and formation time distribution in the spherical collapse model. We also developed an approximation for the ellipsoidal collapse model and applied it to the calculation of the conditional mass function and the halo formation time distribution. For models in which the steps are positively correlated, the halo merger rate is enhanced when the accreted mass is less than similar to 25M*, while for the negatively correlated case this rate is reduced. Compared with the standard model in which the steps are uncorrelated, the models with positively correlated steps produce more aged population in small mass haloes and more younger population in large mass haloes, while for the models with negatively correlated steps the opposite is true. An examination of simulation results shows that a weakly positive correlation between successive merging steps appears to fit best. We have also found a systematic effect in the measured mass function due to the finite volume of simulations. In future work, this will be included in the halo model to accurately predict the three-point correlation function estimated from simulations.
119158957
DISTRIBUTION OF SATELLITE GALAXIES IN HIGH-REDSHIFT GROUPS
We use galaxy groups at redshifts between 0.4 and 1.0 selected from the Great Observatories Origins Deep Survey to study the color-morphological properties of satellite galaxies and investigate possible alignment between the distribution of the satellites and the orientation of their central galaxy. We confirm the bimodal color and morphological-type distribution for satellite galaxies at this redshift range: the red and blue classes correspond to the early and late morphological types, respectively, and the early-type satellites are on average brighter than the late-type ones. Furthermore, there is a morphological conformity between the central and satellite galaxies: the fraction of early-type satellites in groups with an early-type central is higher than those with a late-type central galaxy. This effect is stronger at smaller separations from the central galaxy. We find a marginally significant signal of alignment between the major axis of the early-type central galaxy and its satellite system, while for the late-type centrals no significant alignment signal is found. We discuss the alignment signal in the context of shape evolution of groups.
55450732
WiZard 2: a proposal to complement WiZard detector with two further modules of tracking calorimeter and an accurate spark counter t.o.f. system
Among the several existent proposals for the cosmic antimatter search, the Wi#x005A-0304;ard project for the U.S. Space Station Freedom shows the greatest interest. A possible upgrading of the Wi#x005A-0304;ard apparatus, called Wi#x005A-0304;ard 2, is presented in order to sensibly improve the capability of detecting antihelium nuclei in the cosmic radiation. 
Fra tutte le varie proposte esistenti nell’ambito della ricerca di antimateria cosmica, il progetto Wi#x005A-0304;ard per la Stazione Spaziale americana Freedom si dimostra del piu grande interesse. Si presenta un possibile ampliamento dell’apparato Wi#x005A-0304;ard allo scopo di migliorare sensibilmente la capacita di rivelare nuclei di antielio nella radiazione cosmica.
119286155
Magnetohydrodynamic simulation of the interaction between two interplanetary magnetic clouds and its consequent geoeffectiveness
[1] Numerical studies of the interplanetary “multiple magnetic clouds (Multi-MC)” are performed by a 2.5-dimensional ideal magnetohydrodynamic (MHD) model in the heliospheric meridional plane. Both slow MC1 and fast MC2 are initially emerged along the heliospheric equator, one after another with different time intervals. The coupling of two MCs could be considered as the comprehensive interaction between two systems, each comprising of an MC body and its driven shock. The MC2-driven shock and MC2 body are successively involved into interaction with MC1 body. The momentum is transferred from MC2 to MC1. After the passage of MC2-driven shock front, magnetic field lines in MC1 medium previously compressed by MC2-driven shock are prevented from being restored by the MC2 body pushing. MC1 body undergoes the most violent compression from the ambient solar wind ahead, continuous penetration of MC2-driven shock through MC1 body, and persistent pushing of MC2 body at MC1 tail boundary. As the evolution proceeds, the MC1 body suffers from larger and larger compression, and its original vulnerable magnetic elasticity becomes stiffer and stiffer. So there exists a maximum compressibility of Multi-MC when the accumulated elasticity can balance the external compression. This cutoff limit of compressibility mainly decides the maximally available geoeffectiveness of Multi-MC because the geoeffectiveness enhancement of MCs interacting is ascribed to the compression. Particularly, the greatest geoeffectiveness is excited among all combinations of each MC helicity, if magnetic field lines in the interacting region of Multi-MC are all southward. Multi-MC completes its final evolutionary stage when the MC2-driven shock is merged with MC1-driven shock into a stronger compound shock. With respect to Multi-MC geoeffectiveness, the evolution stage is a dominant factor, whereas the collision intensity is a subordinate one. The magnetic elasticity, magnetic helicity of each MC, and compression between each other are the key physical factors for the formation, propagation, evolution, and resulting geoeffectiveness of interplanetary Multi-MC.
17712450
Cosmic star formation history associated with quasar activity: An approach using the black hole-to-bulge mass correlation
The tight correlation between the masses of central black holes and their host spheroids in nearby galaxies and active galactic nuclei (AGNs) suggests that black hole growth is closely related to their spheroid formation. Based on our previous work regarding such a joint evolutionary scheme and the consequential black hole-to-bulge mass correlation, we use the X-ray luminosity function of AGN and the cosmological evolution rate, which are from ROSAT X-ray surveys, to estimate the cosmic star formation history associated with the black hole growth. By the basic assumption that the major black hole growth occurs during the luminous AGN phase, the luminosity function of AGNs as a function of redshift traces not only the accretion history of the black holes but also the cosmic star formation history of the spheroids. Although the space density of the especially luminous quasars is very low, we show that the total amount of star formation associated with the massive black hole growth is almost the same as that of Lyman break galaxies detected by the current optical deep surveys. We thus argue that the optical deep surveys may miss about half of the net star formation in our universe. This is probably due in part to significant dust extinction, as well as the small field of view of previous optical surveys, which cannot sample such rare events with relatively short timescale. However, the far-infrared emission from the dust heated by ongoing star formation during the black hole growth could sufficiently account for the observed SCUBA number counts and would be the probable dominating energy source of the SCUBA population.
119283904
CMB cold spot from inflationary feature scattering
Abstract We propose a “feature-scattering” mechanism to explain the cosmic microwave background cold spot seen from WMAP and Planck maps. If there are hidden features in the potential of multi-field inflation, the inflationary trajectory can be scattered by such features. The scattering is controlled by the amount of isocurvature fluctuations, and thus can be considered as a mechanism to convert isocurvature fluctuations into curvature fluctuations. This mechanism predicts localized cold spots (instead of hot ones) on the CMB. In addition, it may also bridge a connection between the cold spot and a dip on the CMB power spectrum at l ∼ 20 .
119035074
X-Ray Properties of the Point Source Population in the Spiral Galaxy NGC 5055 （M63） with Chandra
Using Chandra ACIS S3 data we studied the X-ray properties of low-and high-mass X-ray binary populations in the nearby spiral galaxy NGC 5055. A total of 43 X-ray point sources were detected within two effective radii, with 31 sources located on the disk and the rest 12 sources in the bulge. The resolved point sources dominate the X-ray emission of the galaxy, accounting for about 80% of the total counts in 0.3–10 keV. From spectral fittings we calculated the 0.3–10.0 keV luminosities of all the detected X-ray point sources and found that they span a wide range from a few times 1037 erg s−1 to over 1039 erg s−1. After compensating for incompleteness at the low luminosity end, we found that the corrected XLF of the bulge population is well fitted with a broken power-law with a break at 1.57+0.21−0.20×1038 erg s−1, while the profile of the disk population's XLF agrees with a single power-law distribution of slope 0.93+0.07−0.06. The disk population is significantly richer at 2×1038 erg s−1 than the bulge population, indicating that the disk may have undergone relatively recent, strong starbursts that significantly increased the HMXB population, although ongoing starbursts are also observed in the nuclear region. Similar XLF profiles of the bulge and disk populations were found in M81. However, in most other spiral galaxies different patterns of spatial variation of the XLF profiles from the bulge to the disk have been observed, indicating that the star formation and evolution history may be more complex than we have expected.