Day 138

Wednesday.  Today, I'll probably just be reading about magnification, while running shape measurements over Skymaker images in the background.


1111.3359
The HI mass density in galactic haloes, winds and cold accretion as traced by MgII absorption
Kacprzak, Churchill


MgII absorption lines detected in quasar spectra arise from gas structures associated with foreground galaxies, but their mass density is poorly constrained.  Deduce HI from MgII equivalent width, avoid DLAs so that HI comprises accreting and/or outflowing halo gas not locked up in cold neutral clouds.  Omega(HI)_halo ~ 1e-4.  Propose infall/accretion material is sampled by samll W whereas outflow/winds are sampled by large W; find Omega(HI)_infall is consistent with Omega(HI)_outflow for bifurcation at W=1.23 A; cold accretion would then comprise no more than ~7% of the total HI mass density.  Discuss evidence that (1) total HI mass cycling through halos remains fairly constant with cosmic time, accretion of HI gas sustains galaxy winds, (2) evolution in the cosmic star formation rate depends primarily on the rate at which cool HI gas cycles through halos.


1111.3360
Implications of the non-detection of X-ray emission from HD 149427
Stute, Luna


* symbiotic star: slow variable, one red giant and one WD (spectra)
* D'type symbiotic star: has dust emission of 1000K


This particular object, either planetary nebula or D'type symbiotic star, may also be a jet source, and distance unknown.  Observed with X-ray---shows non-detection.  Looks like a symbiotic star onto a white dwarf in hibernation (if symbiotic at all).  


1111.3361
Sizes and surface brightness profiles of quiescent galaxies at z~2
Szomoru, Franx, van Dokkum


Stellar mass-limited sample of quiescent galaxies at 1.5<z<2.5, HST WFC3 observation of GOODS-South.  Find quiescent galaxies at z~2 very closely follow Sersic profiles with n_median = 3.7; no excess flux at large radii.  Their effective radi are a factor ~4 smaller than those at low z of similar mass.  Significant spread in sizes, where the largest is close to the z=0 mass-size relation.  Compare with Virgo cluster galaxies; confirm that most of the mass-growth which occurs between z~2 to now must be due to accretion of material onto the outer regions of the galaxies.  [why outer?]  Investigate evolution in the size distribution of massive quiescent galaxies.  Find that the minimum size growth required for z~2 quiescent galaxies to fall within the z=0 size distribution is a factor ~2 smaller than the total median size growth between z~2 and z=0.


1111.3362
Spectroscopic confirmation of the Dragonfish association: the galaxy's most luminosity OB association [typo in the title!]
Rahman, Moon, Matzner


Confirmed a huge OB association within MW.


1111.3363
Outside-in shrinking of the star-forming disk of dwarf irregular galaxies
Zhang, Hunter, Elmegreen, Gao, Schruba


Representative sample of 34 nearby dwarf irregular (dIrrs) studied, with UV, UBV, Halpha, Spitzer 3.6um in the LITTLE THINGS survey.  Study azimuthal averages of SED, compare with SF histories, and derive surface density distribution and the SF rate averaged over 3 different timescales.  Find that ~80% of the sample galaxies, radial profiles at shorter wavelengths have smaller disk scale lengths than those at longer wavelengths, indicating SF disk has been shrinking.  Also, ~80% of galaxies have steeper mass profiles in the outer disk than in the inner region (piece-wise consistent with exponential profile).  The steep radial decline of SF rate in the outer parts gives a natural explanation for the down-bending SM surface density profiles.  The outside-in growth of SF region is in contrast with the inside-out disk growth scenario suggsted for luminous spiral galaxies.


1111.3370
Measuring the geometry of the universe from weak gravitational lensing behind galaxy groups in the HST cosmos survey
Taylor, Massey, Leauthaud, George, Rhodes, Kitching, Capak, Ellis, Finoguenov, Ilbert, Jullo, Kneib, Koekemoer, Scoville, Tanaka


How does one use weaker lensing signals from multiple sources at different redshifts as geometric tests?  Introduce simple measure of relative shear, which for flat cosmologies separates the effect of lens and source positions into multiplicative terms, allowing signals from many different source-lens pairs to be combined.  Apply to COSMOS, detect a clear variation of shear with distance behind the lens.  


1111.3371
Stellar population gradients in the cores of nearby field E+A galaxies
Pracy et al


Evidence for compact young cores and stellar population gradients which are predicted from models of mergers and tidal interactions which funnel gas into the galaxy core.  Galaxies being seen are in the late stage of a merger where the progenitors have already coalesced.


1111.3372
The stability of dilute plasmas with thermal and composition gradients.  I.  The slow conduction limit: overstable gravity modes
Pessah, Chakraborty


Analyze stability of a dilute plasma with thermal and composition gradients in the limit where conduction is slow compared to the dynamical timescale.  Implications in galaxy cluster where helium has sedimented.


1111.3386
Lyman alpha emitters at redshift z~4.5 in the extended CDF-S region: I. Lyman alpha luminosity function
Zheng, Finkelstein, et al


Ly-alpha luminosity function for the z~4.5 sample is consistent with other published in the literature for 3<z<6, while Ly-alpha luminosity functions in two separate narrowband filters show 2 sigma difference.  This difference is comparable to the differences among z=5.7 and z=6.5 Ly-alpha luminosity functions reported, which are thought to be an implication of cosmic reionization.  


1111.3406
Origin of multiple nuclei in ultraluminous infrared galaxies
Matsui, et al


ULIRGs with >3 nuclei are frequently observed--multiple major mergers?  But theoretical merger rate is too low, so what's going on?  Simulations show that two gas-rich galaxy mergers can generate massive, compact, young star clusters.  Multiple mergers are not necessary to explain multiple nuclei in ULIRGs.


1111.3574
Accretion-driven evolution of BHs: Eddington ratios, duty cycles, and AGN fractions
Shankar, Weinberg, Miralda-Escude


Semi-empirical model of SMBH and AGN populations.  Assume radiative efficiency epsilon and a distribution of Eddington ratios lambda.  Generalize continuity equation models to allow a distribution  P(lambda|M_BH, z), able to draw on constraints from observationally estimated P(lambda) distributions and AGN fractions while accounting for luminosity thresholds of observational samples.  


1111.3591
3DEX: a code for fast Fourier-Bessel decomposition of spherical 3d surveys
Leistedt, Rassat, Refregier, Starck


3D spherical coordinate (Fourier-Bessel) decomposition required.  Fast calculation code made public.


1111.3623
Bar effects on central star formation and AGN activity
Oh, Oh, Yi


Galactic bars are suspected to be channel of gas inflow into the galactic center, and trigger central SF and AGN activity.  SDSS bright galaxy sample has bars in 36% of the face-on spirals.  Bars are found to be more common in galaxies with earlier morphology.  Bar effects on central SF seem higher in redder galaxies.  Bar effects on AGN on the other hand are higher in bluer and less massive galaxies.  These effects more pronounced with increasing bar length.