Day 380

Tuesday.

1302.7026
Probing the extended gaseous regions of M31 with Quasar Absorption lines
Rao, ... York et al

HST-COS spectra of HVCs (high-velocity clouds).  Sightlines have impact parameters ranging between b=13kpc and 112 kpc.  No absorption detected in the four sight lines beyond b=57 kpc.  The 6 remaining sight lines, all at b<32 kpc, and within the N(HI)=3e18/cm^2 boundary of the HI disk of M31, detect low-ionization absorption at M31 velocities along four of them (3 of which include MgII absorption).  Also detect MgII absorption from an HVC.  The velocity location of the low-ion gas tracks the peak in 21 cm emission.  High-ionization absorption is detected along the 3 inner sightlyines, but not along the 3 outer sight lines, for which CIV data exist.  As inferred from 12cm emissiong line maps, only one sightline may have a damped Ly-a system, at b=17.5 kpc; both low and high-ion absorption lines associated with it.  The impact parameters through M31 are similar to the impact parameters of galaxies identified with MgII absorbers at 0.1<z<1.0 in a 2011 study by Rao+.  However, the M31 MgII 2796 rest equivalent widthe values are significantly smaller.  In comparison, moderate-to-strong MgII absorption from MW gas is detected along all 10 sightlines.  This study indicates that M31 does not present itself as an absorbing galaxy, which is typical of higher-z galaxies inferred to give rise to moderate-strength quasar absorption lines.  M31 also appears not to posses and extensive large gaseous cross section, at least not along the direction of its major axis.

1303.0006
The Lyman alpha reference sample: extended Lyman alpha haloes produced at low dust content
Hayes, ... et al

New imaging observations of the Lyman alpha emission line (Lya), performed with HST, that comprise the backbone of the LA reference sample.  Present 14 SB galaxy images at 0.028<z<0.18 in continuum-subtracted Lya, Ha, and the FUV continuum.  Show that Lya is emitted on scales that systematically exceed those of the massive stellar population and recombination nebulae: as measured by the Petrosian 20% radius Lya radii are larger than those of Ha by factors ranging from 1 to 3.6, with an average of 2.4.  The average ratio of Lya to-FUV radii is 2.9.  This suggest that much of the Lya light is pushed to large radii by resonance scattering.  Find the relative Petrosian extension to be uncorrelated with total Lya luminosity, but strongly correlated with dust content, in the sense that a low dust abundance is a necessary requirement in order to spread Lya photons throughout the interstelar medium and drive a large extended Lya halo.

1303.0024
Physical properties of spectroscopically-confirmed galaxies at z>=6.  I.  aBasic characteristics from deep HST and Spitzer observations
Jiang, Egami, ... Fan, ... et al

Present deep HST NIR and Spitzer MIR observations of a large sample of spectro-confirmed galaxies at z>=6.  Sample consists of 51 LAEs at 5.7, 6.5, 7.0, and 16 LBGs at 5.9<z<6.5.  Majority discovered in Subaru Deep field.  Have deep optical in broad and narrow bands with Suprime-Cam.  The NIR images are from WFC3 with a typical depth of 2 orbits in F125W and F160W.  Spitzer MIR images have 3-6 hrs depth in IRAC.  Get redshifts and properties of their rest-frame UV continuum and Lya emission.  These galaxies have steep UV continuum slopes roughly between beta~-1.5 and -3.5, with a median value of beta~-2.3, which is slightly steeper than the slopes of photometrically-selected LBGs reported in previous studies.  The slope shows little dependence on UV continuum luminosity except for a few of the brightest galaxies.  Find a statistically significant excess of galaxies with slopes around beta~-3, suggesting the existence of very young stellar populations with extremely low meatllicity and dust content.  The galaxies have moderately strong rest-frame Lyman-alpha equivalent with in the range of 10 to 300 A.  The SFR derives from the Lya and UV continuum luminosities are also moderate, from a few to a few tens solar masses per year.  The LAEs and LBGs in this sample share many common properties, implying that LAEs represent a subset of LBGs with strong Lya emission.  Finally, derive the UV LFs of LAEs with EW>20 A at z~5.7 and 6.5, and compare them with the UV LFs of LBGs at similar redshifts.

1303.0027
Physical properties of Spectroscopically-confirmed galaxies at z >= 6.  II.  Morphology of te rest-frame UV continuum and Lyman-alpha emission
Jiang, Egami, ... Dave,... et al

Present a detailed structura and morphological study of a large sample of spectroscopically-confirmed galaxies at z>=6, using HST NIR broad-band images and Subaru optical narrow-band images.  Same samples as above.  Galaxies exhibit a wide range of rest-frame UV continuum morphology in the HST images, from compact features to multiple component systems.  The fraction of merging/interaction galaxies reaches 40-50% at M_UV<-20.5 mag, suggesting hierarchical build-up of the brightest galaxies at high z.  Use half-light radius to describe the galaxy sizes, and find that the intrinsic radii r_{hl,in}, after correction for PSF broadening, are roughly between 0.05" and 0.3", with a median value of 0.13" (~0.75 kpc).  This is consistent with the sizes of bright LAEs and LBGs at z>6 in previous studies.  In addition, more luminous galaxies tend to have larger physical sizes, exhibiting a size-luminosity relation r propto L^0.2  The slope 0.2 is significantly flatter than those in previous fainter LBG samples.  Characterize the morphology of z>6 galaxies using nonparameteric methods, including the CAS system, the Gini and M20 parameters.  Compared to low-redshift galaxies, the high-z galaxies appear in slightly different locations in the parameter space, mainly due to their small sizes in the HST images.  However, find strong correlations between the measured parameters, as expected from their definitions.  This implies that these nonparameteric methods could be still applicable for z>=6 galaxies, if used with caution.  Search for extended Lya emission haloes around LAEs at z~5.7 and 6.5, by stacking a number of narrow-band images.  Do not find evidence of extended haloes predicted.

1303.0118
Probing the interactions between the hot plasmas and galaxies in clusters from z=0.1 to 0.9
Gu, et al

With 34 relaxed rich clusters of galaxies with 0.1<z<0.9: study relative spatial distirbutions of the two major baryon contents, the cluster galaxies and the host plasmas.  Determine integrated 2d radial light profiles of member galaxies in each cluster using (1) BG subtraction and (2) color-mag filtering.  The ICM mass profile of each luster in sample, also integrated in two dimensions, was derived from a spatially-resolved spectral analysis using XMM-Newton and Chandra data.  Then, the radially-integrated light profile of each cluster was divided by its ICM mass profile, to obtain a profile of "galaxy light vs ICM mass ratio".  The ratio profiles over the central 0.65 R500 regions were found to steepen from the higher- to lower-redshift subsamples, meaning that the galaxies become more concentrated in the ICM sphere towards lower redshifts.  The evolution is also seen in galaxy number vs. ICM mass ratio profiles.  A range of systematic uncertainties in the galaxy light measurements, as well as many radius-/redshift- dependent biases to the galaxy vs ICM profiles have been assessed, but none of them is significant against the observed evolution.  Besides, the galaxy light vs. total mass ratio profiles also exhibit gradual concentration towards lower redshift.  Interpret in the context that galaxies, the ICM, and the DM components followed a similar spatial distribution in the early phase (z>0.5), while the galaxies have fallen towards the center relative to the others at a later phase.

1303.0219
The distribution of AGN covering factors
Lawrence et al

Review knowledge of the most basic properties of the AGN obscuring region - its location, symmetry, and mean covering factor - and discuss new eviidence on the distribution of covering factors in a sample of ~9k quasars with WISE, UKIDSS, and SDSS photoemtry.  The obscuring regions of AGN may be in some ways more complex than thought - multi-scale, asymmetric, chaotic - and in some ways simpler - wth no dependence on luminosity, and a covering factor distribution that may be determined by the simplest of considerations - e.g. random misalignments.

1303.0285
The meaning and consequences of star formation criteria in galaxy models with resolved stellar feedback
Hopkins, Narayanan, Murray

Use high-res sims to consider the effects of different SF criteria on galactic scales, with explicitly resolved GMCs and stellar feedback.  Compare (1) a self-gravity criterion, (2) a fixed density threshold, (3) a molecular gas law, (4) a temperature threshold, (5) a Jeans-instability requirement, (6) a criteria that cooling times be shorted than dynamical times, and (7) a convergent-flow criterion.  All models (MW-like or high-density starbursts) produce identical integrated SFRs in agreement with Kennicutt relation.  Without ffeedback all produce order-of-mag excessive SFRs; totally dependent on feedback and independent of the SF law.  But the spatial and density distribution of SF depend strongly on the SF criteria.  Because cooling rates are generally fast and gas is turbulent, criteria (4)-(7) are 'wak' and spread SF uniformly over the disk.  A molecular criterion (3) localizes to higher densities, but still a wide range [?]; for metallicity near solar, it is simiar to a density threshold at n~1/cm^3 (well below mean densities in the MW center of starbursts).  Fixed density thresholds (2) can always select the highest densities, but must be adjusted for simulation resolution and galaxy properties; the same threshold that works in a MW-like simulation will select nearly all gas in a starburst.  Binding criteria (1) tend to adaptively select the largest over-densities, independent of galaxy model or resolution, and automatically predict clustered SF.  Argue that this SF model is most physically-motivated and presets significant numerical advantages in large-dynamic range simulations.

Combining clustering and abundances of galaxy clusters to test cosmology and primordial non-Gaussianity
Mana, Giannantonio, Weller, Hoyle, Huetsi, Sartoris

Present clustering of galaxy clusters as a useful addition to the common set of cosmological observables.  The clustering of clusters probes the large-scale structure of the Universe, extending galaxy clustering analysis to the high-peak, high-bias regime.  Clustering of galaxy clusters complements the traditional cluster number counts and observable-mass relation analysis, significantly improving their constraining power by breaking existing calibration degeneracies.  Use the maxBCG galaxy clusters catalogue to constrain cosmological parameters and cross-calibrate the mass-observable relation, using cluster abundances in richness bins and weak-lensing mass estimates.  Then add the redshift-space power spectrum of the sample, including an effective modeling of the weakly non-linear contribution and allowing for an arbitrary photometric redshift smoothing.  The inclusion of the PS data allows for an improved self-calibration of the scaling relation.  Find that the inclusion of the power spectrum typically brings a ~50% improvement in the errors on the fluctuation amplitude sigma_8 and the matter density Omega_m.  Finally, apply this method to constrain models of the early universe though the amount of primordial non-Gaussianity of the local type, using both the variation in the halo mass function and in the cluster bias.  Find a constraint on the amount of skewness f_NL = 12 pm 157 (1 sig) from the cluster data alone.