Day 641

Monday.

1404.6250
The redshift evolution of the mean temperature, pressure, and entropy profiles in 80 SPT-selected galaxy clusters
McDonald, .. Vikhlinin, et al

80 clusters in 2500 deg2 SPT + Chandra observation.  Divide into subsamples of ~20 clusters based on z and central density, performing an X-ray fit to all clusters in a subsample simultaneously, assuming self-similarity of the temperature profile.  This approach allows to constrain the shape of the temperature profile over 0<r<1.5R500, which would be impossible on a per-cluster basis (individual clusters only have 2000 X-ray photon counts).  Find that high-z (0.6<z<1.2) clusters are slightly (~40%) cooler both in the inner (r<0.1 R500) and outer (r>R500) regions than their low-z (0.3<z<0.6) counterparts.  Combining the average temperature profile with measured gas density profiles from the earlier work, infer the average pressure and entropy profiles for each subsample.  Overall, observed pressure profiles agree well with earlier lower-z measurements, suggesting minimal z evolution in the pressure profile outside of the core.  Find no measurable z evolution in the entropy profile at r<0.7R500.  Observe a slight flattening of the entropy profile at r>R5000 in the high-z subsample.  This flattening is consistent with a temperature bias due to the enhanced (~3x) rate at which group-mass (~2 keV) halos, which would go undetected at the survey depth, are accreting onto the cluster at z~1.  This work demonstrates a powerful method for inferring spatially-resolved cluster properties in the case where individual cluster signal-to-noise is low, but the number of observed clusters is high.

1404.6251
Overconsumption, outflows and the quenching of satellite galaxies
McGee, Bower, Balogh

The baryon cycle of galaxies is a dynamic process involving the intake, consumption and ejection of vast quantities of gas.  In contrast, the conventional picture of satellite galaxies has them methodically turning a large gas reservoir into stars until this reservoir is forcibly removed due to external ram pressure---this picture needs revision.  The modern understanding of the baryon cycle suggests that in some regimes the simple interruption of the fresh gas supply may quench satellite galaxies long before stripping events occur, a process dubbed "overconsumption".  Compile measurement from the literature of observed satellite quenching times at a range of redshifts to determine if satellites are principally quenched through orbit-based gas stripping events -- either direct stripping of the disk (ram pressure) or the extended gas halo (strangulation) -- or from internally-driven SF outflows via overconsumption.  The observed timescales show significant deviation from the evolution expected for gas stripping mechanisms and suggest that either ram pressure stripping is much more efficient at high z, or that secular outflows quench satellites before orbit-based stripping occurs.  Given the strong z evolution of SFRs, at high z (>1.5) even moderate outflow rates will lead to extremely short quenching times with the expectation that such satellites will be quenched almost immediately following the cessation of cosmological inflow, regardless of stripping events.  Observations of high z satellites give an indirect but sensitive measure of the outflow rate with current measurements suggesting that outflows are no larger than 2.5x the SFR for galaxies with a stellar mass of 1e10.5 Msun.  

1404.6442
Sparse representation of photometric redshift PDFs: preparing for petascale astronomy
Kind, Brunner

Widespread adoption of photo-z PDFs.  Both current and future photometric surveys are expected to obtain images of billions of distinct galaxies.  As a result, storing and analyzing all of these PDFs will be non-trivial and even more severe if a survey plans to compute and store multiple different PDFs.  In this paper, propose the use of a sparse basis representation to fully represent individual photo-z PDFs.  By using an Orthogonal Matching Pursuit algorithm and a combination of Gaussian and Voigt basis functions, demonstrate how the approach is superior to a multi-Gaussian fitting, as approximately half of the parameters are required for the same fitting accuracy with the additional advantage that an entire PDF can be stored by using a 4-byte integer per basis function, and can achieve better accuracy by increasing the number of bases.  By using data from CFHTLenS, demonstrate that only 10 to 20 points per galaxy are sufficient to reconstruct both the individual PDFs and the ensemble redshift distribution, N(z), to an accuracy of 99.9% when compared to the one built using the original PDFs computed with a resolution of delta z = 0.01, reducing the required storage of 200 original values by a a factor of 10 to 20.  Finally, demonstrate how this basis representation can be directly extended to a cosmological analysis, thereby increasing computational performance without losing resolution nor accuracy.

1404.6458
The flux of kilogram-sized meteoroids from lunar impact monitoring
Suggs, Moser, Cooke, Suggs

The flashes from meteoroid impacts on the Moon are useful in determining the flux of impactors with masses as low as a few tens of grams.  A routine monitoring program at NASA's Marshall Space Flight Center has recorded over 300 impacts since 2006.  A selection of 126 flashes recorded during priers of photometric skies was analyzed, creating the largest and most homogeneous dataset of lunar impact flashes to date.  Standard CCD photometric techniques were applied to the video and the luminous energy, kinetic energy, and mass are estimated for each impactor.  Shower associations were determined for most of the impactors and a range of luminous efficiencies was considered.  The flux to a limiting energy of 2.5e-6 kT TNT or 1.05e7 J is 1.03e-7 /km^2/hr and the flux to a limiting mass of 30g is 6.14e-10 /m^2/yr at the Moon.  Comparison made with measurements and models of the meteoroid population indicate that the flux of objects in this size range is slightly lower (but within error bars) than flux at the size from the near Earth object and fireball population by Brown+2002.  Size estimates for the crater detected by Lunar Reconnaissance Orbiter from a large impact observed on March 17, 2013 are also briefly discussed.