Day 592

Wednesday.

1402.4129
The luminosity function at z~8 from 97 Y-band dropouts: inferences about reionization
Schmidt, Treu, et al

BoRG (Brightest of Reionizing Galaxies) survey with 350 arcmin^2 of HST V-, Y-, J- and H-bands: largest search to dat for z~8 LBGs; total of 38 BoRG LBGs (z~8 candidates).  Estimate LF in Bayesian formalism, including a likelihood based on the correct binomial distribution instead of Poisson.  97 galaxies when including a fainter sample from Bouwens+2012 from HUDF and ERS.  Show that z~8 LF well described by Schechter function with M*=-20.15, faint end slope of alpha=-1.87, and a number density of log_10 phi*=-3.24.  Integrated down to M=-17.7, this LF yields a luminosity density log_10 epsilon [erg/s/Hz/Mpc^3] = 25.52.  The LF analysis is consistent with previous values.  Implications: assuming priors on the clumping factor and the photon escape fraction, show that the UV LF from galaxy samples down to M=-17.7 can ionize only 10-50% of the neutral hydrogen at z~8.  Full reionization would require extending the LF down to M=-15.  [but there is no observations there, right?]

1402.4139
Galaxy And Mass Assembly (GAMA): testing galaxy formation models through the most massive galaxies in the Universe
Oliva-Altamirano, … et al

883 GGGs and GCGs in GAMA: compare stellar mass of BGGs and BCGs in groups and clusters of similar dynamical masses, find no significant growth [in stellar mass?] between z=0.27 and z=0.09.  Also examine the number of BGGs/BCGs that have line emission, finding that approximately 65% of BGGs/BCGs show Ha in emission.  From the galaxies where the necessary spectroscopic lines were accurately recovered (54% of the sample), find that half of this harbor on-going SF with rates up to 10 Msun/yr, and the other half have an AGN at the center [is it because of the SF that the lines exist?].  BGGs are more likely to have ongoing SF, while BCGs show a higher fraction of AGN activity.  By examining the position of the BGGs/BCGs with respect to their host DM halo, find that around 13% of them do not lie at the center of the DM halo.  This could be an indicator of recent cluster-cluster mergers.  Conclude that BGGs and BCGs acquired their stellar mass rapidly at higher redshifts as predicted by SAMs, mildly slowing down at low redshifts.

1402.4170
A free-form lensing grid solution for A1689 with new multiple images
Diego, Broadhurst, Benitez, Umetsu, Coe, … et al

Many SL in A1689, resolving substructures ~25 kpc across.  Examine A1689 non-parametrically, combining SL images and WL from wider imaging, and incorporate member galaxies to improve the lens solution.  Strongly lensed galaxies are often locally affected by member galaxies, however, these perturbations cannot be recovered in grid based reconstructions because the lensing information is too spares to resolve member galaxies.  By adding luminosity-scaled member galaxy deflections to the smooth grid, can derive meaningful solutions with sufficient accuracy to permit the identification of the strongly lensed images, so the model becomes self consistent.  Identify 11 new multiply lensed system candidates and clarify previously ambiguous cases, and the deepest optical and NIR data from Hubble and Subaru.  Improved spatial resolution brings up new features and not seen when the weak and strong lensing effects are used separately, including clumps and filamentary DM around the main halo.  This treatment allows an objective mass ratio between the cluster and galaxy components, for examining the extent of tidal stripping of the luminous member galaxies.  FInd a typical M/L_B=21 inside the r<1 arc minute region that drops to M/L_B=17 inside the r<40 arc second [isn't that smaller than 1 arcrminute?] region.  Model independence means objectively evaluating the competitiveness of stacking cluster lenses for defining the geometric lensing-distance-redshift relation in a model independent way.

1402.4217
Mass-galaxy offsets in Abell 3827, 2218 and 1689: intrinsic properties or line-of-sight substructures?
Mohammed, Liesenborgs, Saha, Williams

Mass mass of 3 clusters to test for mass-light offsets.  Use GRALE for minimum assumptions [on mass distribution] independent of light distribution.  In 3827 and 2218, find local mass peaks in the central regions that are displaced form the nearby galaxies to a few to several kpc, which appear to be intrinsic.  For A1689, see no significant offsets in the central region, but do detect a possible LoS structure: it appears only when sources at z>3 are used for reconstructing the mass. Discuss possible origins of the mass-galaxy offsets in A3827 and 2218: these include pure gravitational effects like dynamical friction, but also non-standard mechanisms like self-interacting DM.

1402.4429
The origin and optical depth of ionizing photons in the Green Pea galaxies
Jaskot, Oey

GP galaxies are similar to high-z galaxies in their morphologies and SFRs and are tools for probing the generation and transmission of ionizing photons.  The GPs contain massive star clusters that emit copious amounts of high-energy radiation, as indicated by intense [OIII] 5007 and HeII 4686 emission.  Focus on 6 GP galaxies with high ratios of [OIII]/[OII]>~10.  Such high ratios indicate gas with a high ionization parameter or a low optical depth.  The GP line ratios and ages point to chemically homogeneous massive stars, WR stars, or shock ionization as the most likely sources of the HeII emission.  Models including shock ionization suggest that the GPs may have low optical depths, consistent with a scenario in which ionizing photons escape along passageways created by recent SNe.  The GPs and similar galaxies can shed new light on cosmic reionization by revealing how ionizing photons propagate from massive star clusters to the IGM.

1402.4461
The impact of galaxy formation on the total mass, profiles and abundance of haloes
Velliscig, van Daalen, Schaye, McCarthy, Cacciato, LeBrun, Vecchia

Use cosmo hydro-sims to investigate how the inclusion of physical processes relevant to galaxy formation (SF, metal-line cooling, stellar winds, SNe and feedback from AGN) change the properties of haloes, over 4 orders of magnitude in mass.  Find that gas expulsion and the associated DM expansion induced by SN-driven winds are important for halos with M200<1e13 Msun, lowering their masses by up to 20% relative to DM-only model.  AGN feedback, which is required to prevent overcooling, has a significant impact on halo masses all the way up to cluster scales (M200~1e15 Msun).  Baryonic physics changes the total mass profiles of haloes out to several times the virial radius, a modification that cannot be captured by a change in the halo concentration.  The decrease in the total halo mass causes a decrease in the halo MF of about 20%.  This effect can have important consequences for abundance matching technique as well as for most SAM of galaxy formation.  Provide analytic fitting formulae, derived from simulations that reproduce the observed baryon fractions, to correct halo masses and mass functions from DM-only simulations.  The effect of baryonic physics (AGN feedback in particular) on cluster member counts is about as large as changing the cosmology from WMAP7 to Planck, even when a moderately high mass limit of M500~1e14 Msun is adopted.  Thus, for precision cosmology the effects of baryons must be accounted for.