Tracing outflows and accretion: a bimodal azimuthal dependence of MgII absorption
Kacprzak, Churchill, Nielsen
Report bimodality in the azimuthal angle distribution of gas around galaxies as traced by MgII absorption: Halo gas prefers to exist near the projected galaxy major and minor axes. From 88 spectroscopically confirmed MgII absorption-selected galaxies, and 35 confirmed non-absorbing galaxies imaged with HST and SDSS. The azimuthal angle distribution for non-absorbers is flat, indicating no azimuthal preference for gas with Mg absorption. Find blue SF galaxies clearly drive the bimodality. Compute azimuthal angle dependent MgII absorption covering fraction, find that it is enhanced by as much as 20-30% along the major and minor axes [a cross?]. Combined results highly suggestive that the bimodailty is driven by gas accreted along the galaxy major axis and outflowing along the galaxy minor axis [oooh!]. The opening angle of outflows is 2.5 larger than for accreting gas. Find the probability of detecting outflows is 60%, implying that winds are more commonly observed. Scenario is consistent with ideas of galaxy evolution where SF galaxies accrete new gas reservoirs, forming stars and producing winds, while red early-type galaxies exist passively due to a lock of new gas reservoirs to form new stars.
1205.0248
hase reddening on near-Earth asteroids: implications for mineralogical analysis, space weathering and taxonomic classification
Sanchez, et al
* S-complex asteroids:
* Q-type asteroids:
Lab spectral tests of ordinary chondrites at phase angles from 13 deg to 120 deg to see if "phase reddening" is observable (an effect that produces an increase of the spectral slope and variations in the strength of the absorption bands as the phase angle increases). Find: both asteroid and meteorite spectra show an increase in bad depths with increasing phase angle---significant increase with increasing phase angle for g>30 degree. Increase in spectral slope caused by phase reddening is comparable to certain degree of space weathering---an increase in phase angle in the range of 30 degree to 120 degree will produce a reddening of the reflectance spectra equivalent to exposure times of 0.1e6 to 1.3e6 years at about 1AU about the Sun. Find: under some circumstances phase reddening could lead to an ambiguous taxonomic classification of asteroids.
1205.0249
Circum-galactic gas and the isotropic gamma ray background
Feldmann, Hooper, Gnedin
Interaction of CR with interstellar gas and radiation fields of MW provide most of the gamma rays observed by Fermi Gamma Ray Space Telescope. Gas densely concentrated along the galactic disk, hydrodynamical simulations and observational evidence favor the presence of a halo of hot (T~1e6 K) ionized hydrogen (H_II) extending with non-gengligible densities out to the virial radius of the MW. Show that CR collisions with the circum-galactic gas should be expected to provide a significant flux of gamma rays, on the order of 10% of the observed isotopic gamma ray BG at energies above 1 GeV. In addition, gamma rays originating from the extended HII haloes of other galaxies along a given LoS should contribute to this BG at a similar level.
1205.0253
The radius of baryonic collapse in disc galaxy formation
Kassin, Devriendt, Fall, de Jong, Allgood, Primack
Observations indicate the disc galaxies typically have only about half as much specific angular momentum as their DM haloes. Argue that this does not necessarily imply that baryons lose this much specific angular momentum as they form galaxies, but instead, indicate that galaxies are most directly related to the inner regions of their host haloes, as may be expected in a scenario where baryons in the inner parts of haloes collapse first. [ah ha]. Limiting case examined under the idealized assumption of perfect angular momentum conservation. Under the assumption that galaxies are related to haloes via their characteristic rotation velocities, the necessary Delta is ~600. This Delta corresponds to an average halo radius and mass which are ~60% and ~75% of the virial radius. Refer to this radius as the radius of baryonic collapse, since if specific angular momentum is conserved perfectly, baryons would come from within it (an effective radius) [?]. The difference between the predicted initial and observed final specific angular momentum of galaxies, which is conventionally attributed solely to angular momentum loss, can more naturally be explained by a preference for collapse of baryons within R_BC, with possibly some later angular momentum transfer.
1205.0256
Reconciling stellar dynamical and hydrostatic X-ray mass measurements of an elliptical galaxy with gas rotation, turbulence and magnetic fields
Humphrey, Buote, Brighenti, Gebhardt, Mathews
Hydrostatic X-ray studies of ISM in early-types underestimate the gravitating mass compared to stellar dynamics, implying deviations from exact hydrostatic equilibrium. Combine both measurements in Bayesian statistics to allow non thermal pressure or bulk motions in the hot ISM to be constrained. Demonstrate accuracy of the method with hydrosims; find significant but subdominant non thermal pressure fraction (0.27 pm 0.06) in the central part of the galaxy; imply 360 km/s random turbulence or B-field of 40 muG, whereas gas rotation alone is unlikely to explain the detailed non thermal profile. Future observations with Astro-H can detect turbulence or gas rotation.
1205.0270
The circumgalactic medium of massive galaxies at z~3: a test for stellar feedback, galactic outflows, and cold streams
Shen, Madau, Guedes, Mayer, Prochaska
New rests on the kinematics, thermal and ionization state, and spatial distribution of metal-enriched gas in the circumgalactic medium (CGM) of massive galaxies at redshift 3, using "Eris" suite of cosmological simulations. SNe feedback producing galactic outflows, a SF recipe based on high gas density threshold, metal-dependent radiative cooling, and model for diffusion of metals and thermal energy. Multiphase CGM produce interstellar absorption line stregths of Lya, CII, CIV, SiII, and SiIV as a function of galactocentric impact parameter in broad agreement with observation. Only about 1/3 of all gas within R_vir is outflowing. The fraction of sight lines within one virial radius that intercept optically thick material is 27%, in agreement with rent observations. Such optically thick absorption trace inflowing "cold" streams that penetrate deep inside the virial radius. The streams, enriched to metallicities above 0.01 solar, give origin to strong CII absorption. Galactic outflows do not cause any substantial suppression of the cold accretion mode. The central galaxy is surrounded by a large OVI halo, with near unity covering factor out to 150 kpc This matches the trends observed in SF galaxies.
1205.0311
Dark matter in the Milky Way's dwarf spheroidal satellites
Walker
Review article of dSph satellites; implications for cosmology and particle nature of DM.
1205.0430
Progress in understanding the diffuse UV cosmic background
Henry
From Voyager UV spectrometer observations, preliminary investigation seems to confirm a component of diffuse UV BG that is not dust-scattered starlight.
1205.0474
Non-Gauassian structure of the lensed CMB power spectra covariance matrix
Benoit-Levy, Smith, Hu
GL of CMB encodes cosmo info in the observed anisotropies of temperature and polarization. Accurate extraction of this additional information requires precise modeling of the covariance matrix of the power spectra of observed CMB fields. Introduce a new analytical model to describe the non-Gaussian structure of this covariance matrix; display the importance of 2nd order terms that were previously neglected. Compared with direct numerical simulations, model captures parameter errors to better than a few percent for cases where the non-Gaussianity causes an order unity degradation in errors. Also provide detailed comparison between the information content of lensed CMB power spectra and ideal reconstruction of the lensing potential. Illustrate the impact of the non-Gaussian terms in the power spectrum covariance by providing Fisher errors on the sum of the masses of the neutrinos, the dark energy equation of state, and the curvature of the universe.
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