2038251
Time-dependent Ionization in Radiatively Cooling Gas
We present new computations of the equilibrium and nonequilibrium cooling efficiencies and ionization states for low-density radiatively cooling gas containing the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe. We present results for gas temperatures between 10^4 and 10^8 K, assuming dust-free and optically thin conditions, and no external radiation. For nonequilibrium cooling we solve the coupled time-dependent ionization and energy loss equations for a radiating gas cooling from an initially hot, ≳5 × 10^6 K, equilibrium state, down to 10^4 K. We present results for heavy element compositions ranging from 10^(-3) to 2 times the elemental abundances in the Sun. We consider gas cooling at constant density (isochoric) and at constant pressure (isobaric). We calculate the critical column densities and temperatures at which radiatively cooling clouds make the dynamical transition from isobaric to isochoric evolution. We construct ion ratio diagnostics for the temperature and metallicity in radiatively cooling gas. We provide numerical estimates for the maximal cloud column densities for which the gas remains optically thin to the cooling radiation. We present our computational results in convenient online figures and tables.
118162733
Inward bound: studying the Galactic Centre with NAOS/CONICA
We report on the first results obtained using adaptive optics measurements of the Galactic Centre done with NAOS/CONICA.
119297976
THE SINS/zC-SINF SURVEY OF z ∼ 2 GALAXY KINEMATICS: EVIDENCE FOR POWERFUL ACTIVE GALACTIC NUCLEUS-DRIVEN NUCLEAR OUTFLOWS IN MASSIVE STAR-FORMING GALAXIES*
We report the detection of ubiquitous powerful nuclear outflows in massive (≥10{sup 11} M {sub ☉}) z ∼ 2 star-forming galaxies (SFGs), which are plausibly driven by an active galactic nucleus (AGN). The sample consists of the eight most massive SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging spectrometer SINFONI, six of which have sensitive high-resolution adaptive optics-assisted observations. All of the objects are disks hosting a significant stellar bulge. The spectra in their central regions exhibit a broad component in Hα and forbidden [N II] and [S II] line emission, with typical velocity FWHM ∼ 1500 km s{sup –1}, [N II]/Hα ratio ≈ 0.6, and intrinsic extent of 2-3 kpc. These properties are consistent with warm ionized gas outflows associated with Type 2 AGN, the presence of which is confirmed via independent diagnostics in half the galaxies. The data imply a median ionized gas mass outflow rate of ∼60 M {sub ☉} yr{sup –1} and mass loading of ∼3. At larger radii, a weaker broad component is detected but with lower FWHM ∼485 km s{sup –1} and [N II]/Hα ≈ 0.35, characteristic for star formation-driven outflows as found in the lower-mass SINS/zC-SINF galaxies. The high inferredmore » mass outflow rates and frequent occurrence suggest that the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles and may thus contribute to the process of star formation quenching in massive galaxies. Larger samples at high masses will be crucial in confirming the importance and energetics of the nuclear outflow phenomenon and its connection to AGN activity and bulge growth.« less
119211945
THE SINS/zC-SINF SURVEY of z ∼ 2 GALAXY KINEMATICS: OUTFLOW PROPERTIES*
Using SINFONI H{alpha}, [N II], and [S II] AO data of 27 z {approx} 2 star-forming galaxies (SFGs) from the SINS and zC-SINF surveys, we explore the dependence of outflow strength (via the broad flux fraction) on various galaxy parameters. For galaxies that have evidence for strong outflows, we find that the broad emission is spatially extended to at least the half-light radius ({approx}a few kpc). Decomposition of the [S II] doublet into broad and narrow components suggests that this outflowing gas probably has a density of {approx}10-100 cm{sup -3}, less than that of the star-forming gas (600 cm{sup -3}). There is a strong correlation of the H{alpha} broad flux fraction with the star formation surface density of the galaxy, with an apparent threshold for strong outflows occurring at 1 M{sub Sun} yr{sup -1} kpc{sup -2}. Above this threshold, we find that SFGs with log m{sub *} > 10 have similar or perhaps greater wind mass-loading factors ({eta} = M-dot{sub out}/SFR) and faster outflow velocities than lower mass SFGs, suggesting that the majority of outflowing gas at z {approx} 2 may derive from high-mass SFGs. The mass-loading factor is also correlated with the star formation rate (SFR), galaxy size, andmore » inclination, such that smaller, more star-forming, and face-on galaxies launch more powerful outflows. We propose that the observed threshold for strong outflows and the observed mass loading of these winds can be explained by a simple model wherein break-out of winds is governed by pressure balance in the disk.« less
8929448
EVIDENCE FOR WARPED DISKS OF YOUNG STARS IN THE GALACTIC CENTER
The central parsec around the supermassive black hole in the Galactic center (GC) hosts more than 100 young and massive stars. Outside the central cusp (R ~ 1'') the majority of these O and Wolf-Rayet (W-R) stars reside in a main clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the GC with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured W-R/O stars in the central 12'' and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of 4 compared to our earlier work. Based on the sample of 90 well measured W-R/O stars, we develop a detailed statistical analysis of their orbital properties and orientations. We show that half of the W-R/O stars are compatible with being members of a clockwise rotating system. The rotation axis of this system shows a strong transition from the inner to the outer regions as a function of the projected distance from Sgr A*. The main clockwise system either is either a strongly warped single disk with a thickness of about 10°, or consists of a series of streamers with significant radial variation in their orbital planes. Eleven out of 61 clockwise moving stars have an angular separation of more than 30° from the local angular momentum direction of the clockwise system. The mean eccentricity of the clockwise system is 0.36 ± 0.06. The distribution of the counterclockwise W-R/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state: 10 out of 29 counterclockwise moving W-R/O stars have an angular separation of more than 30° from the local angular momentum direction of the counterclockwise system. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young massive stars.
118435899
Ultra-compact High Velocity Clouds as Minihalos and Dwarf Galaxies
We present dark matter minihalo models for the Ultra-Compact, High-Velocity H I Clouds (UCHVCs) recently discovered in the 21?cm ALFALFA survey. We assume gravitational confinement of 104?K H I gas by flat-cored dark-matter subhalos within the Local Group. We show that for flat cores, typical (median) tidally stripped cosmological subhalos at redshift z = 0 have dark-matter masses of ~107 M ? within the central 300?pc (independent of total halo mass), consistent with the Strigari mass scale observed in low-luminosity dwarf galaxies. Flat-cored subhalos also resolve the mass discrepancy between simulated and observed satellites around the Milky Way. For the UCHVCs, we calculate the photoionization-limited hydrostatic gas profiles for any distance-dependent total observed H I mass and predict the associated (projected) H I half-mass radii, assuming the clouds are embedded in distant (d 300?kpc) and unstripped subhalos. For a typical UCHVC (0.9?Jy?km s?1), we predict physical H I half-mass radii of 0.18 to 0.35?kpc (or angular sizes of 0.'6 to 2.'1) for distances ranging from 300?kpc to 2?Mpc. As a consistency check, we model the gas-rich dwarf galaxy Leo T, for which there is a well-resolved H I column density profile and a known distance (420?kpc). For Leo T, we find that a subhalo with M 300 = 8 (? 0.2) ? 106 M ? best fits the observed H I profile. We derive an upper limit of P HIM 150?cm?3?K for the pressure of any enveloping hot intergalactic medium gas at the distance of Leo T. Our analysis suggests that some of the UCHVCs may in fact constitute a population of 21?cm-selected but optically faint dwarf galaxies in the Local Group.
31215380
X-ray orbital modulations in intermediate polars
We present an analysis of 30 archival ASCA and RXTE X-ray observations of 16 intermediate polars to investigate the nature of their orbital modulation. We show that X-ray orbital modulation is widespread amongst these systems, but not ubiquitous as indicated by previous studies that included fewer objects. Only seven of the sixteen systems show a clearly statistically significant modulation depth whose amplitude decreases with increasing X-ray energy. Interpreting this as due to photoelectric absorption in material at the edge of an accretion disc would imply that such modulations are visible for all system inclination angles in excess of 60 degrees. However, it is also apparent that the presence of an X-ray orbital modulation can appear and disappear on a timescale of ∼years or months in an individual system. This may be evidence for the presence of a precessing, tilted accretion disc, as inferred in some low mass X-ray binaries.
1239184
General Relativistic Effects in the Core Collapse Supernova Mechanism
We apply our recently developed code for spherically symmetric, fully general relativistic (GR) Lagrangian hydrodynamics and multigroup flux-limited diffusion (MGFLD) neutrino transport to examine the effects of GR on the hydrodynamics and transport during collapse, bounce, and the critical shock reheating phase of core collapse supernovae. GR effects were examined by performing core collapse simulations from several precollapse models in the Newtonian limit, in a hybrid limit consisting of GR hydrodynamics and Newtonian transport, and in the fully GR limit. Comparisons of models computed with GR versus Newtonian hydrodynamics show that collapse to bounce takes slightly less time in the GR limit and that the shock propagates slightly farther out in radius before receding. After a secondary quasi-static rise in the shock radius, the shock radius declines considerably more rapidly in the GR simulations than in the corresponding Newtonian simulations. During the shock reheating phase, core collapse computed with GR hydrodynamics results in a substantially more compact structure from the center out to the stagnated shock, the shock radius being reduced by a factor of 2 after 300 ms for a 25 M model and 600 ms for a 15 M model, times being measured from bounce. The inflow speedmore » of material behind the shock is also increased by about a factor of 2 throughout most of the evolution as a consequence of GR hydrodynamics. Regarding neutrino transport, comparisons show that the luminosity and rms energy of any neutrino flavor during the shock reheating phase increases when switching from Newtonian to GR hydrodynamics. This arises from the close coupling of the hydrodynamics and transport and the effect of GR hydrodynamics to produce more compact core structures, hotter neutrinospheres at smaller radii. On additionally switching from Newtonian to GR transport, gravitational time dilation and redshift effects decrease the luminosities and rms energies of all neutrino flavors. This decrease is less in magnitude than the increase in neutrino luminosities and rms energies that arise when switching from Newtonian to GR hydrodynamics, with the result that a fully GR simulation gives higher neutrino luminosities and harder neutrino spectra than a fully Newtonian simulation of the same precollapse model.« less
119095544
Final state interactions and new physics in B ---> pi K decays
Within the standard model, and if one assumes that soft rescattering effects are negligible, the $\mathrm{CP}$ asymmetry ${\mathcal{A}}_{\mathrm{CP}}^{\mathrm{dir}}{(B}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}K)$ is predicted to be very small and the ratio ${R=B(B}_{d}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{\mp}}{K}^{\ifmmode\pm\else\textpm\fi{}}{)/B(B}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}K)$ provides a bound on the angle $\ensuremath{\gamma}$ of the unitarity triangle, ${\mathrm{sin}}^{2}\ensuremath{\gamma}l~R.$ We estimate the corrections from soft rescattering effects using an approach based on Regge phenomenology, and find effects of order $10%$ with large uncertainties. In particular, we conclude that ${\mathcal{A}}_{\mathrm{CP}}^{\mathrm{dir}}\ensuremath{\sim}0.2$ and ${\mathrm{sin}}^{2}\ensuremath{\gamma}\ensuremath{\sim}1.2R$ could not be taken unambiguously to signal new physics. Using SU(3) relations, we suggest experimental tests that could constrain the size of the soft rescattering effects thus reducing the related uncertainty. Finally, we study the effect of various models of new physics on ${\mathcal{A}}_{\mathrm{CP}}^{\mathrm{dir}}$ and on $R.$
73563531
Metastability of the false vacuum in a Higgs-seesaw model of dark energy
In a recently proposed Higgs-Seesaw model the observed scale of dark energy results from a metastable false vacuum energy associated with mixing of the standard model Higgs particle and a scalar associated with new physics at the GUT or Planck scale. Here we address the issue of how to ensure metastability of this state over cosmological time. We consider new tree-level operators, the presence of a thermal bath of hidden sector particles, and quantum corrections to the effective potential. We find that in the thermal scenario many additional light degrees of freedom are typically required unless coupling constants are somewhat fine-tuned. However quantum corrections arising from as few as one additional light scalar field can provide the requisite support. We also briefly consider implications of late-time vacuum decay for the perdurance of observed structures in the universe in this model.