Day 683

Monday.

1406.5183
On the correlation between metallicity and the X-shaped morphology of the Milky Way bulge
Nataf et al

The trend of the X-shape being more pronounced among the more metal-rich stars may have been overestimated, as it is relatively easier to detect a bimodality in the distance distribution function at higher metallicities.

1406.5187
Kinematic evolution of simulated star-forming galaxies
Kassin et al

Recent observations have shown that SF galaxies like MW evolve kinematically into ordered thin disks over the last ~8B yrs since z=1.2, undergoing a process of "disk settling".  For the first time, study the kinematic evolution of a suite of four state of the art "zoom in" hydro sims of galaxy formation and evolution n a fully cosmological context and compare with these observations.  Until now, robust measurements of the internal kinematics of simulated galaxies were lacking as the simulations suffered from low resolution, overproduction of stars, and overly massive bulges.  The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis.  Show that simulated galaxies follow the same kinematic trends as read galaxies: they progressively decrease in disordered motions (sigma_g) and increase in ordered rotation (Vrot) with time.  The slopes of the relations between both sigma_g and Vrot with redshift are consistent between the simulations and the observations.  In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations, and they both have similarly large scatter.  This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling.

1406.5196
Constraints on the alignment of galaxies in galaxy clusters from $\sim$15,000 spectroscopic members
Sifón, Hoekstra, Cacciato, Viola, et al

Torques acting on galaxies lead to physical alignments, but the resulting ellipticity correlations are difficult to predict.  As they constitute a major contaminant for cosmic shear studies, it is important to constrain the IA signal observationally.  Measure the alignments of satellite galaxies within 91 massive galaxy clusters in 0.05<z<0.55 and quantify their impact on the cosmic shear signal.  Combine a sample of 38k galaxies with spec-z with ihg-quality data from CFHT.  Use phase information to select 15k cluster members, 14k of which have shape measurements, and measure 3 different types of alignment: the radial alignment of satellite galaxies towards the BCGs, the common orientations of satellite galaxies and BCGs, and the radial alignments of satellites with each other.  Residual systematic effects are much smaller than the statistical uncertainties.  Detect no galaxy alignment of any kind out to at least 3r200.  The signal is consistent with zero for both blue and red galaxies, bright and faint, and also for subsamples of clusters based on redshift, dynamical mass, and dynamical state.  These conclusions are unchanged if the sample is increased with bright clusters members from the red sequence.  Augment constraints with those from the literature to estimate the importance of the IA of satellites compared to that of central galaxies, for which the alignments are described by the linear alignment model.  Find that the additional contribution from satellite can be ignored for current cosmic shear surveys such as KiDS, and that the linear alignment model is accurate enough to model IA for these surveys.

1406.5250
Alignments of the galaxies in and around the Virgo cluster with the local velocity shear
Lee, Rey, Kim

Observational evidence presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster.  The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog recently constructed by Kim+ are used to determine the direction of the local sheet.  The peculiar velocity field reconstructed from the SDSS DR7 is analyzed to estimate the local velocity shear tensor at the Virgo center.  Showing first that the minor principal axis of the local velocity shear tensor is almost parallel to the line of sight direction, detect a clear signal of alignment between the positions of the Virgo satellite and the intermediate principal axis of the local velocity shear projected onto the plane of the sky.  Furthermore, the dwarf satellites are found to appear more strongly aligned than the normal counterparts, which is interpreted as indication of the following: (i) the normal and the dwarf satellites fall in the Virgo cluster preferentially along the local filament and the local sheet, respectively.  (ii) the local filament is aligned with the minor principal axis of the local velocity shear while the local sheet is in parallel to the plane spanned by the minor and they intermediate principal axes.  Result is consistent with the recent numerical claim that the velocity shear is a good tracer of the cosmic web.

1406.5459
Dependence of the cosmic microwave background lensing power spectrum on the matter density
Pan, Knox, White

Provide an analytic explanation of the matter in which the lensing of CMB anisotropies deneds on the matter density, finding that the dominant effete comes from the shape of the matter PS set by the decay of small-scale potentials between horizon crossing and matter-radiation equality.