Day 759

Tuesday.

1410.1193
redMaPPer IV: photometric membership identification of cluster galaxies with 1% precision
Rozo, Rykoff, Becker, Reddick, Wechsler

In order to study the galaxy population of galaxy cluster with photometric data one must be able to accurately discriminate between cluster members and non-members.  The redMaPPer cluster finding algorithm treats this problem probabilistically.  Here, utilize SDSS and GAMA spectroscopic membership rates to validate the redMaPPer membership probability estimates for clusters with z in [0.1,0.3].  Find small - but correctable - biases, sourced by 3 different systematics.  The first two were expected a priori, namely blue cluster galaxies and correlated structure along the LoS.  The third systematics is new: the redMaPPer template fitting exhibits a non-trivial dependence on photometric noise, which biases the original redMaPPer probabilities when utilizing noisy data.  After correcting for these effects, find exquisite agreement (~1%) between the photometric probability estimates and the spectroscopic membership rates, demonstrating that it is possible to robustly recover cluster membership estimates from photometric data alone.  As a byproduct of our analysis, find that on average unavoidable projection effects from correlated structure contribute ~6% of the richness of a redMaPPer galaxy cluster.  This work also marks the second public release of the SDSS redMaPPer cluster catalog.
1410.0962
Accounting for cosmic variance in studies of gravitationally-lensed high-redhsift galaxies in the Hubble Frontier Field clusters
Robertson, Ellis, et al

SL provides a powerful means for studying faint galaxies in the distant universe.  By magnifying the apparent brightness of BG sources, massive cluster enable the detection of galaxies fainter than the usual sensitivity limit for blank fields.  However, this gain in effective sensitivity comes at the cost of a reduced survey volume and, in this Letter, demonstrate there is an associated increase in the cosmic variance uncertainty.  As an example, show that this cosmic variance uncertainty of the high z population viewed through the HST FF cluster Abell 2744 increases from ~35% at z~7 to >~65% at z~10.  Previous studies of high z galaxies identified in the FF have underestimated the cosmic variance uncertainty that will affect the ultimate constraints on both the faint end slope of the high-z luminosity function and the cosmic SFR density, key goals of the FF program.

1410.1033
Weak Lensing by minifilament of mini void as the origin of flux-ratio anomalies in lensed quasar MG0414+0534
Inoue

Explore the WL effects by mini structures in the LoS in a quadruply lensed quasar that shows an anomaly in the flux ratios.  Find that the observed flux-ratio anomaly can be explained by a presence of either a mini filament or a mini void in the LoS with a surface mass density of the order 1e8-9 Msun/h/arcsec^2 without taking into account any sub haloes in the lensing galaxy.  The astrometric perturbation by a possible minifilament/minivoid is <~0.001 arc sec and the amplitudes of convergence perturbations due to these perturbs are ~0.004-0.008 at the place of an image that shows anomaly.  In order to discriminate models with the LoS mini structures from those with a sub halo(s) in the lensing galaxy, need to precisely measure the projected convergence and shear around the lensing galaxy.  The differential magnification effect could break the model degeneracy if the source size is >~100 pc.  Observation at the sub millimeter band using interferometers will enable determination of the origin of anomalies in the flux ratios.

1410.1241
Sussing merger trees: the impact of halo merger trees on galaxy properties in a semi-analytic model
Lee, ... Behroozi, et al

A halo merger tree forms the essential back bone of a SAM for galaxy formation and evolution.  Recent studies have pointed out that extracting merger trees from numerical simulations of structure formation is non-trivial; different tree building algorithms can give differing merger histories.  These differences should be carefully understood before merger trees are used as input for models of galaxy formation.  Investigate the impact of different halo merger trees on a SAM.  Find that the z=0 galaxy properties in the model show differences between trees when using a common parameter set.  The SFH of the universe and the properties of satellite galaxies can show marked differences between trees with different construction methods.  Independently calibrating the SAM for each tree can reduce the discrepancies between the z=0 global galaxy properties, at the cost of increasing the differences in the evolutionary histories of galaxies.  Furthermore, the underlying physics implied can vary, resulting in key quantities such as the SN feedback efficiency differing by factors of 2.  Such a change alters the regimes where SF is primarily suppressed by supernovae.  Therefore, halo merger trees extracted from a common halo catalogue using different, but reliable, algorithms can result in a difference in the SAM.  Given the uncertainties in galaxy formation physics, however, these differences may not necessarily be viewed as significant.