Day 608

Saturday.  Old posts to catch up with.  Sunday.

1402.0687
Ultra compact dwarfs in the Perseus Cluster: UCD formation via tidal stripping
Penny et al

Present the results of a Keck/DEIMOS survey of UCDs in Perseus cluster core.  Confirm cluster memberships for 14 UCDs, with radial velocities ~5300 km/s.  Two of these confirmed Perseus UCDs have extremely blue colors (B-R<0.6 mag), reside in SF filaments surrounding NGC 1275, and have likely formed as massive star clusters in the last ~100 Myr.  Also measure a central velocity dispersion of a third, UCD13 (sigma_0=38pm8 km/s), the most extended UCD in the sample.  Determine it to have radius R_e=85pm1.1 pc, a dynamical mass of (2.3pm0.8)e8 Msun, and a metallicity [Z/H] = -0.52pm0.3 dex.  UCD13 and the cluster's central galaxy have a projected separation of 30 kpc and a radial velocity difference of ~20 km/s.  Based on its size, red color, internal velocity dispersion, dynamical mass, metallicity and proximity to NGC 1275, argue that UCD13 is likely the remnant nucleus of a tidally stripped dE, with this progenitor dE having M_B~-16 mag and mass ~1e9 Msun.

1402.0697
Constraining the mass-concenetration relation through weak lensing peak function
Mainini, Romano

Halo masses and concentrations have been studied extensively, by means of N-body sims as well as observationally, during the last decade.  Nevertheless, the exact form of the mass-concentration relation is still widely debated.  One of the most promising method to estimate masses and concentrations relies on gravitational lensing from massive halos.  Investigate the impact of the mass-concentration relation on halo peak abundance in WL shear maps relying on the aperture mass method for peak detections.  After providing a prescription to take into account the concentration dispersion (always neglected in previous works) in peak number counts predictions, assess their power to constrain the mass-concentration relation by means of Fisher matrix technique.  Find that, when combined with different cosmo probes, peak statistics information from near-future WL surveys provides an interesting and complementary alternative method to lessen the long standing controversy about the mass-concentration relation.

1402.0725
The brighter-fatter effect and pixel correlations in CCD sensors
Antilogus et al

Present evidence that spots imaged using astronomical CCDs do not exactly scale with flux: bright spots tend to be broader than faint ones, using the same illumination pattern.  Measure that the linear size of spots or stars, of typical size 3 to 4 pixels FWHM, increase linearly with their flux by up to 2% over the full CCD dynamic range.  This brighter-fatter effect affects both deep-depleted and thinned CCD sensors.  Propose that this effect is a direct consequence of the distortions of the drift electric field sourced by charges accumulated within the CCD during the exposure and experienced by forthcoming light-induced charges in the same exposure.  The pixel boundaries then become slightly dynamical: overfilled pixels become increasingly smaller than their neighbors, so that bright star sizes, measured in number of pixels, appear larger than those of faint stars.  This interpretation of the brighter-fatter effect implies that pixels in flat-fields should exhibit statistical correlations, sourced by Poisson fluctuations, that is indeed detected.  Propose to use the measured correlations in flat-fields to derive how pixel boundaries shift under the influence of a given charge pattern, which allows to quantitatively predict how star shapes evolve with flux.  This physical model of the brighter-fatter effect also explains the commonly observed phenomenon that the spatial variance of CCD flat-fields increases less rapidly than their average.

1402.0866
Bulge growth and quenching since z=2.5 in CANDELS/3D-HST
Lang, .. Dekel, Genzel, Bell, Faber, Grogin, Koekemoer, Primack,... et al

Exploiting the deep high-resolution imaging of all 5 CANDELS fields, and accurate redshift information provided by 3D-HST, investigate the relation between structure and stellar populations for a mass-selected sample of 6764 galaxies above 1e10 Msun, spanning 0.5<z<2.5.  Fit 2-d models comprising a single Sersic fit and two-cpomonent (bulge+disk) decompositions not only to the H-band, but also to the stellar mass maps reconstructed from resolved stellar population modeling.  Confirm that the increased bulge prominence among quiescent galaxies, as reported previously based on rest-optical observations, remains in place when considering the distributions of stellar mass.  Moreover, observe and increase of the typical Sersic index and bulge-to-total ratio (with median B/T reaching 40-50%) among SF galaxies above 1e11 Msun.  Given that quenching for these most massive systems is likely to be imminent, findings suggest that significant bulge growth precedes a departure from the SF MS.  Demonstrate that the bulge mass (and ideally knowledge of the bulge and total mass) is a more reliable predictor of the SF vs. quiescent state of a galaxy than the total stellar mass.  The same trends are predicted by the state-of-the-art SAM by Somerville et al.  In the latter, bulges and BHs grow hand in hand through merging and/or disk instabilities, and AGN-feedback shuts off SF.  Further observations will be required to pin down SF quenching mechanisms, but results imply they must be internal to the galaxies and closely associated with bulge growth.

1402.0867
The big problems in star formation: the star formation rate, stellar clustering, and the initial mass function
Krumholz

Review: discuss the current state of the field of star formation, focusing on 3 central questions: what controls the rate at which gas in a galaxy converts to stars?  What determines how those stars are clustered, and what fraction of the stellar population ends up in gravitationally-bound structures?  What determines the stellar IMF, and does it vary with SF environment?  Use these 3 question as a lens to introduce the basis of SF, beginning with a review of the observational phenomenology and the basic physical processes.  Then review the status of current theories that attempt to solve each of the 3 problems, pointing out links between them and opportunities for theoretical and numerical work that crosses the scale between them.  Conclude with a discussion of prospects for theoretical progress in the coming years.

1402.0868
ICM cooling, AGN feedback and BCG properties of galaxy groups-Five properties where groups differ from clusters
Bharadwaj, Reiprich, Schellenberger, Eckmiller, Mittal, Israel

Sample of 26 galaxy groups from Chandra: constrain the central cooling times (CCTs) of the ICM and classify the groups as strong cool-core (SCC), weak cool-core (WCC) and non-cool-core(NCC) based on their CCTs.  The total radio luminosity of the BCG obtained using radio catalog data and literature, compared to the CCT to understand the link between gas cooling and radio output.  Determine K-band luminosities of the BCG with 2MASS data, and use it to constrain the masses of the SMBH, which were then compared to the radio output.  Also tested for correlations between the BCG luminosity and the overall X-ray luminosity and mass of the group.  The observed cool-core/non-cool-core fractions for groups are comparable to those of clusters.  However, notable differences are seen.  For clusters, all SCCs have a central temperature drop, but for groups, this is not the case as some SCCs have centrally rising temperature profiles.  While for the cluster sample, all SCC clusters have central radio sources as opposed to only 45% of the NCCs, for the group sample, all NCC groups have a central radial source as opposed to 77% of the SCC groups.  For clusters, there are indications of an anti correlation trend between radio luminosity and CCT which is absent for the groups.  Indications of a trend of radio luminosity with BH mass observed in SCC clusters is absent for groups.  The strong correlation observed between the BCG luminosity and the cluster X-ray luminosity/cluster mass weakens significantly for groups.  Conclude that there are important differences between clusters and groups within the ICM cooling/AGN feedback paradigm.

1402.0888
The MassiveBlack-II simulation: the evolution of haloes and galaxies to z~0
Khandai et al

Investigate the properties of haloes, galaxies and BHs to z=0 in high-res hydro sim MBII which evolves a LCDM cosmology in a comoving volume Vbox=100(Mpc/h)^3.  MBII is the highest resolution simulation of this size which includes a self-consistent model for SF, BH accretion and associated feedback.  Provide a simulation browser web application which enables interactive search and tagging of haloes, sub halos and their properties and publicly release the galaxy catalogs.  Analysis of the halo MF in MBII reveals that baryons have strong effects, with changes in the halo abundance of 20-35% below the knee of the MF (Mhalo<1e13.2Msun/h at z=0) when compared to fits based on DM only simulations.  Provide a fitting function for the halo MF out to z=11 and discuss how the onset of non-universality in the MF limits the accuracy of the fit.  Study the HOD and clustering of galaxies, in particular the evolution and scale dependence of stochasticity and bias, finding reasonable agreement with observational data.  The shape of the cosmic SED predicted by MBII is consistent with observations, but lower in amplitude.  The galaxy stellar mass function (GSMF) is broadly consistent with observations at z>=2.  At z<2, the population of passive low mass (for M*<1e9 Msun) galaxies in MBII makes the GSMF too steep compared to observations, whereas at the high mass end (M*>1e11 Msun) galaxies hosting bright AGNs make significant contributions to the GSMF.  The quasar bolometric luminosity function is also largely consistent with observations.  Note however that more efficient AGN feedback (behind simple thermal coupling used here) is likely necessary for the largest, rarest objects/clusters at low redshifts.