Day 619

Tuesday.

1403.7524
Star-forming blue ETGs in two newly discovered galaxy over densities in the HUDF at z=1.84 and 1.9: unveiling the progenitors of passive ETGs in cluster cores
Mei, … Newman, … Grogin, Koekemoer, … et al

Present two galaxy over densities in UDF: a proto-cluster at z=1.84, M200=2.2e14Msun from velocity dispersion and X-ray; and a group at z=1.90.  Neither overdensity shows evidence of a red sequence.  About 50% of their members show interactions and/or disturbed morphologies, which are a signature of merger remnants.  Most of their morphologically classified ETGs have blue colors and show recent SF.  These observations reveal large fractions of spectroscopically confirmed SF blue ETGs in protoclusters at z~2.  These are most likely among the progenitors of the quiescent population in clusters at more recent epochs.  Their mass-size relation is consistent with that of passive ETGs in clusters at z~0.7-1.5.  If these galaxies are the progenitors of cluster ETGs at these lower redshifts, their size would evolve according to a similar mass-size relation.  It is noteworthy that quiescent ETGs in clusters at z=1.8-2 also do not show any significant size evolution over this redshift range, contrary to field ETGs.  [I suppose they are not compact?]  The ETG fraction of the sample is <40%, compared to typically quiescent ETG fraction of ~80% in cluster cores at z<1.  The fraction, masses and colors of the newly discovered ETGs imply that the other cluster ETGs will be formed/accreted at later time.

1403.7525
The life and death of cosmic voids
Sutter, .. Hamaus, et al

Investigate the formation, growth, merger history, movement, and destruction of cosmic voids detected via the watershed transform in a cosmological N-body DM LCDM simulation.  By adapting a method used to construct halo merger trees, able to trace individual voids back to their initial appearance and record the merging and evolution of their progenitors at high z.  For the scales of void sizes captured in the simulation, find that the void formation rate peaks at scale factor 0.3, which coincides with a growth in the void hierarchy and the emergence of DE.  Voids of all sizes appear at all scale factors, though the median initial void size decreases with time.  When voids become detectable, they have nearly their present-day [comoving?] volumes.  Almost all voids have relatively stable growth rates and suffer only infrequent minor mergers.  Dissolution of a void via merging is very rare.  Instead, most voids maintain their distinct identity as annexed sub voids of a larger parent.  The smallest voids are collapsing at the present epoch, but void destruction ceases after scale factor 0.3.  In addition, voids centers tend to move very little, less than 0.01 of their effective radii per ln a, over their lifetimes.  Overall, most voids exhibit little radical dynamical evolution; their quiet lives make them pristine probes of cosmological ICs and the imprint of DE.

1403.7531
Galaxy pairs in the Sloan Digital Sky Survey - IX: Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer
Satyapal et al

Interactions between galaxies are predicted to cause gas inflows that can potentially trigger nuclear activity.  Since the inflowing material can obscure the central regions of interacting galaxies, a potential limitation of previous optical studies is that obscured AGNs can be missed at various stages along the merger sequence.  Present the first large MIR study of AGNs in mergers and galaxy pairs, in order to quantify the indigence of obscured AGNs triggered by interactions.  The sample consists of galaxy pairs and post-mergers drawn from SDSS that are matched to detections by WISE.  Find that the fraction of AGN in the pairs, relative to a mass-, z- and environment-matched control sample, increases as a function of decreasing projected separation.  This enhancement is most dramatic in the post-merger sample, where a factor of 10-20 excess in the AGN fraction is found compared to the control. Although this trend is in qualitative agreement with results based on optical AGN selection, the MIR selected AGN excess increases much more dramatically in the post-mergers than is seen for optical AGN.  Results suggest that energetically dominant optically obscured AGNs become more prevalent in the most advanced mergers, consistent with theoretical predictions.

1403.7669
An implementation of Bayesian lensing shear measurement
Sheldon

The Bayesian gravitational shear estimation algorithm developed by Bernstein and Armstrong (2014) can potentially be used to overcome noise bias and recover shear using very low S/N galaxy images.  In that work, the authors confirmed the method is sufficiently unbiased for planned surveys (fractional error <2e-3) in a simplified demonstration, but no test was performed on images.  Present a full implementation for fitting models to galaxy images, including the effects of PSF and pixelization.  Test the implementation using simulated galaxy images modeled as Sersic n=1 and 4, convolved with a PSF and a flat pixel response function.  Use a round Gaussian model for the PSF and to avoid potential PSF-fitting errors.  Simulate galaxies with mean observed, post-PSF FWHM =1.2*(FWHM_PSF), with log-normal scatter.  Also drew fluxes from a log-normal distribution.  Produced independent simulations, each with pixel noise tuned to produce different mean S/N ranging from 10-1000.  Applied a constant shear to all images.  Fit the simulated images to a model with the true Sersic index to avoid modeling biases.  Recovered the input shear with fractional error less than 2e-3 in all cases, confirming that, in these controlled conditions, the method is sufficiently unbiased for planned surveys.

1403.7836
Early-type galaxy star formation histories in different environments
Fitzpatrick, Graves

Use very high-S/N stacked spectra of 29k nearby ETGs from SDSS to investigate variations in their SFHs with environment at fixed position along and perpendicular to the FP.  Define three classifications of local group environment based on the 'identities' of galaxies within their DM haloes: central BGGs (brightest group galaxies), Satellites, and Isolateds (those 'most massive' in a a DM halo with no satellites).  Find that the SFHs of quiescent ETGs are almost entirely determined by their structural parameters sigma and Delta I_e.  Any variation with local group environment at fixed structure is only slight: satellites have the oldest stellar populations, 0.02 dex older than BGGs and 0.04 older than Isolateds; BGGs have the highest Fe-enrichments, 0.01 dex higher than Isolateds and 0.02 dex higher than Satellites; there are no differences in the Mg-enhancement between BGGs, Isolateds, and Satellites.  Observation that, to zeroth-order, the SFHs of quiescent ETGs are fully captured by their structures places important qualitative constraints on the degree to which late-time evolutionary processes (those which occur after a galaxy's initial formation and main SF lifetime) can alter their SFHs/structures.

1403.7966
Black hole accretion preferentially occurs in gas rich galaxies
Vito … Viero, et al

Gas content of ~few hundred AGN host galaxies at z<1, and compared it with a sample of inactive galaxies, matched in bins of M* and z.  Gas mass inferred from IR-inferred dust mass, under reasonable assumptions and metallicity scaling relations for the dust-to-gas ratio.  Find that AGNs are on average hosted in galaxies much more gas rich than inactive galaxies.  … Difference is up to a factor of ten higher in low stellar mass galaxies, with a significance of 6.5 sigma.  In almost half of the AGN sample the gas content is 3x higher than in the control sample of inactive galaxies.  Result strongly suggests that the probability of having an AGN activated is simply driven by the amount of gas in the host galaxy; this can be explained in simple terms of statistical probability of having a gas cloud falling into the gravitational potential of the BH.  The increased probability of an AGN being hosted by a SF galaxy, identified by previous works, may be a consequence of the relationship between gas content and AGN activity, found in this paper, combined with the Schmidt-Kennicutt law for SF.

1403.8049
Neutrinos help reconcile Planck measurements with both Early and local universe
Dvorkin, Wyman, Rudd, Hu

In light of the recent BICEP2 B-mode polarization detection, re-examine the evidence for an extra sterile massive neutrino, originally invoked to account for the tension between the CMB PS and local measurements of the expansion rate H0 and cosmological structure.  With only the standard active neutrinos and power-law scalar spectra, this detection is in tension with the upper limit of r<0.11 (95% CL) from the lack of corresponding low multipole excess in the temperature anisotropy from gravitational waves.  An extra sterile species with the same energy density as is needed to reconcile the CMB data with H0 measurements can also alleviate this new tension.  By combining data from the Planck and ACT/STP temperature spectra, WMAP9 polarization, H0, BAO and local cluster abundance measurements with BICEP2 data, find the joint evidence for a sterile massive neutrino increases to DeltaNeff=0.81pm0.25 for the effective number and ms=0.47pm0.13 eV for the effective mass or 3.2 sigma and 3.6 sigma evidence respectively.