Day 294

Monday.  Chaaarge!  (into astro-ph)

1209.1387
Constraints on the ionizing efficiency of the first galaxies
Alvarez, Finlator, Trenti

Just enough photons to maintain the universe in an ionized state at z~5-6; The ionizing emissivity must have been larger at earlier times in order to yield the extended reionization history implied by CMB.  Address the possibility that a faint population of galaxies with host halo masses 1e8-9 Msun dominated the ionizing photon budget at z>9, due to their must higher escape fractions.  Such faint, early galaxies would not have formed in ionized regions (UV heating suppresses it), and hence would not contribute to the ionizing BG at z<6.  Model matches (1) low escape fractions observed for high-z galaxies, (2) the WMAP constraint of tau_es~0.09, (3) low values for UVB at z<6, and (4) the observed SFR density inferred from Lyman-break galaxies.  A top-heavy PopIII not required in this scenario.  Low mass galaxies possess high escape fraction, then escape fraction can increase strongly towards high z.

1209.1389
Reproducing the stellar mass/halo mass relation in simulated LCDM galaxies: theory vs observational estimates
Munshi et al

Present-day total stellar-to-halo mass ratio (SHM) as a function of halo mass for a new sample of simulated field galaxies with cosmological LCDM high-res SPH+N-body simulations.  (Metal line cooling, dust and self-shielding, H2 based star formation and SNe driven gas outflows included).  18 simulated halos range from 1e8 to 1e12 Msun.  At z=0 simulated galaxies have baryon content and morphology typical of field galaxies.  Good agreement with SHM in simulations and present-day predictions from abundance matching technique of Moster+(2012).  Improvement of simulation is due to decreasing of SHM ratio because of (1) gas outflows reducing SF efficiency, but allow for formation of cold gas component (2) estimating stellar masses of simulated galaxies using artificial observations (3) accounting for a systematic (30%) overestimate in total halo masses in DM-only simulations, due to neglect of baryon loss over cosmic times.  Analysis suggests that stellar mass estimates based on photometric magnitudes can underestimate the contribution of old stellar populations to the total stellar mass [!], leading to stellar mass errors of up to 50% for individual galaxies.  Must use proper comparison between observation and simulation; this may reduce the perceived tension between SF efficiency in galaxy formation models and in real galaxies.

1209.1391
The density profiles of massive, relaxed galaxy clusters: I. the total density over 3 decades in radius
Newman, Treu, Elis, Sand, Nipoti, Richard, Jullo

Use SL and WL with resolved stellar kinematics within BCG to get the radial density profile of 7 massive, relaxed clusters, over 3kpc to 3Mpc.  Lensing mass typically agree with x-ray estimate within 15% (departure from hydrostatic equilibrium is small), and clusters are not strongly elongated along the line of sight.  Inner log slope nearly universal, with a mean of 1.16 and intrinsic scatter of <0.13 (1 sigma).  Homogeneous shape of observed velocity dispersion profiles.  Slope agrees with numerical sims of DM only, despite the significant contribution of stellar mass.  The NFW profile characteristic of collisionless cold dark matter is a better description of the total mass density at r>~5-10 kpc than that of DM alone [???].  Hydro sims that include baryons, cooling and feedback currently provide a poorer match.  Discuss significance for understanding assembly of BCGs and cluster cores, particularly the influence of baryons on the inner DM halo.

1209.1392
The density profiles of massive, relaxed galaxy clusters: II. separating luminous and dark matter in cluster cores
Newman, Treu, Ellis, Sand

Decompose the inner mass profiles of these clusters into stellar and DM components.  Parameterizing the DM density profile as a power law on small scales, find mean slope 0.50.  Alternatively, cored NFW profiles with 1.14 provide an equally good description.  Significantly shallower than the canonical NFW models at r>30 kpc, comparable to the effective radii of the BCGs.  The inner DM profile correlated with the distribution of stars in the BCG, demonstrating a close connection between the inner halo and the assembly of stars in the central galaxy.  The stellar M/L ratio inferred from lensing and stellar dynamics is consistent with that inferred using stellar population synthesis models if a Salpeter IMF is adopted.  Compare results to theories describing the interaction between baryons and DM in cluster cores, including prescriptions for adiabatic contraction, and discuss possible signatures of alternative DM candidates.

1209.0458
The hidden fortress: structure and substructure of the complex strong lensing cluster SDSS J1029+2623
Oguri, Schrabback, .. Kochanek, .. Blandford, .. et al

HST imaging of 3-image quasar lens system lensed by z=0.584 cluster.  6 additional multiply imaged galaxies!  Bimodal mass distribution (deviates from Chandra measurements).  Einstein radius 15.2" for quasar at z=2.197.  M_vir = 1.5e14 Msun/h, c_vir=25.7 [!]  Lensing mass estimate smaller than x-ray by 2x.  Mass discrepancy from shock heating of intracluster gas during a merger.  

1209.0459
Dense molecular gas: a sensitive probe of stellar feedback models
Hopkins, Narayanan, Murray, Quartaert

Show: mass fraction of GMC gas (n>100 cm^-3) in dense SF clumps, observable in dense molecular tracers (HCN/CO(1-0)), is a sensitive probe of the strength and mechanism(s) of stellar feedback.  From high-res simulations with pc-scale resolution and explicit models for feedback from radiation pressure, photoionization heating, stellar winds, and SNe, make predications for the dense molecular gas tracers as a function of GMC and galaxy properties and the efficiency of stellar feedback.  In models of weak/no feedback, much of the mass in GMCs collapses into dense sub-units, HCN/CO ratio 10x larger than observed.  With feedback, good agreement with observations.  Changing the strength or timing of SNe tends to move systems along, rather than off, the HCN-CO relation (because SNe heat lower-density material, not the high-density gas).  Changing the radiation pressure (which acts efficiently in high density gas) has a much stronger effect on HCN than on CO.  Predict: fraction of dense gas (HCN/CO) increases with increasing GMC surface density, drives a trend in HCN/CO with SFR and luminosity which has tentatively been observed.  

1209.0463
Looking at the relation between haloes and galaxies under the lens
Neistein, Khochfar

Use empirical approach to model the stellar mass of galaxies according to their hot DM haloes and subhaloes (HASH), where each galaxy resides in a sub halo from N-body sims.  Study the mass ratio (sub haloes and galaxies) using: WL, 2pt CF, and stellar mass function of galaxies.  Model lensing signal directly from cosmo simulation.  Find WL does not provide a strong constraint on the MR (factor of 10 freedom in subhalo mass of central galaxies for a given stellar mass).  [Not sure what they're talking about when they say lensing signal.  gg lensing?]

1209.0467
Tracking down the source population responsible for the unresolved cosmic 6-8 keV background
Xue, .. D. Schneider, et al

Find 6845 X-ray undetected galaxies that dominates the unresolved 20-25% of the 6-8 keV cosmic X-ray background. Mostly 1<z<3, 25<z_850<28, 2e8<M*/Msun<2e9 galaxies (majority of X-ray detected AGNs are in massive (>1e10Msun) galaxies).  Evidence for relatively low-mass galaxies hosting highly obscured AGNs.

1209.0586
On the orbital and internal evolution of cluster galaxies
Iannuzzi, Dolag

Galaxies in cluster experience significant evolution in their orbital motions throughout time; also in their hot/cold gas content and SF properties.  Do the changes in the internal properties happen in parallel with those in the orbital motion, or are the orbital features at the time of infall what determines the fate of the member galaxies?  Are the properties of galaxies at a given time related to the coeval orbital anisotropy, or are they better related to the anisotropy at infall?  Study Millennium Sim.  Sort by age, SFR and color, study anisotropy profile.  Conclude: orbital properties at infall strongly influence the subsequent evolution of the internal features of galaxies; overall anisotropy of the galaxy population tends to increase with time.

1209.0671
Remote sensing of Chiral signatures on Mars
Sparks, et al

Describe circular polarization as a remote sensing diagnostic of chiral signatures which may be applied to Mars.  The remarkable phenomenon of homochirality provides a unique bio-signature which can be amenable to remote sensing through circular polarization spectroscopy.  Observations of selected areas of the Mars surface could reveal chiral signatures and hence explore the possibility of extant or preserved biological material.