Day 866

Monday.

1504.02483
The MASSIVE survey II: stellar population trends out to large radius in massive early type galaxies
Greene, Janish, Ma, McConnell, Blakeslee, Thomas, Murphy

Examine stellar population gradients in ~100 massive early type galaxies spanning 180<sigma*<370 km/s and M_K of -22.5 to -26.5 mag, observed as part of the MASSIVE survey (Ma+2014).  Using IFS, create stacked spectra as a function of radius for galaxies binned by their stellar velocity dispersion, stellar mass, and group richness.  With excellent sampling at the highest stellar mass, examine radial trends in stellar population properties extending to beyond twice the effective radius (~2.5 R_e). Examine radial trends in age, metallicity, and in the abundance ratios of Mg, C, N, and Ca, and discuss the implications for SFHs and elemental yields.  When weighted to a fixed physical radius of 3-6 kpc (the likely size of the galaxy cores formed at high z), stellar age and [Mg/Fe] increase with increasing sigma* and depend only weakly on stellar mass, as might be expected if denser galaxies form their central cores earlier and faster.  If instead focus on trends weighted towards R_e, the trends in abundance and abundance ratio weaken, as might be expected if the stars at large radius were accreted by smaller galaxies.  Finally, show that when controlling for sigma*, there are only very subtle differences in stellar populations properties or gradients as a function of group richness; even at large radius internal properties matter more than environment in determining SFH.


1504.02510
Tidal alignment of galaxies
Blazek, Vlah, Seljak

Develop an analytic model for galaxy IA based on the theory of tidal alignment.  Calculate all relevant NL corrections at one-loop order, including effects from NL density evolution, galaxy biasing, and source density weighting.  Contributions from density weighting are found to be particularly important and lead to bias dependence of the IA amplitude, even on large scales.  This effect may be responsible for much of the luminosity dependence in IA observations.  The increase in IA amplitude for more highly biased galaxies reflects their locations in regions with large tidal fields.  Also consider the impact of smoothing the tidal field on halo scales.  Compare the performance of this consistent NL model in describing the observed alignment of luminous red galaxies with the inner model as well as the frequently used "nonlinear alignment model," finding a significant improvement on small and intermediate scales.  Also show that the cross-correlation between density and IA (the "GI" term) can be effectively separated into source alignment and source clustering, and accurately model the observed alignment down to the one-halo regime using the tidal field from the fully NL halo-matter cross correlation.  Inside the one-halo regime, the average alignment of galaxies with density tracers no longer follows the tidal alignment prediction, likely reflecting NL processes that must be considered when modeling IA on these scales.  Finally, discuss tidal alignment in the context of cosmic shear measurements.


1504.02662
Detection of spatial correlations of fundamental plane residuals, and cosmological implications
Joachimi, Singh, Mandelbaum

The FP is a widely used tool to investigate the properties of early-type galaxies, and the tight relation between its parameters has spawned several cosmo applications, including its use as a distance indicator for peculiar velocity surveys and as a means to suppress intrinsic noise in cosmic size magnification measurements.  Systematic trends with the large-scale structure across the FP could cause serious biases for these cosmo probes, but may also yield new insights into the early-type population.  Report the first detection of spatial correlations among offsets in galaxy size from an FP that explicitly accounts for z trends, using a sample of about 95k elliptical galaxies from the SDSS.  Show that these offsets correlate with the density field out to at least 10 Mpc/h at 4 sigma significance in a way that cannot be explained by systematic errors in galaxy size estimates.  Propose a physical explanation for the correlation by dividing the sample into central, satellite, and field galaxies, identifying trends for each galaxy the separately.  Central (satellite) galaxies lie on average above (below) the FP, which is argued could be due to a higher (lower) than average M/L ratio.  Fit a simple model to the correlations of FP residuals and use it to predict the impact on peculiar velocity PS, finding a contamination larger than 10% for k>0.04 h/Mpc.  Moreover, cosmic magnification measurements based on a n FP could be severely contaminated over a wide range of scales by the intrinsic FP correlations.