Day 886

Wednesday.


1505.02781
Mapping stellar content to dark matter halos using galaxy clustering and galaxy-galaxy lensing in the SDSS DR7
Zu, Mandelbaum

The mapping between the distributions of the observed galaxy stellar mass and the underlying dark matter haloes provides the crucial link from theories of large-scale structure formation to interpreting the complex phenomena of galaxy formation and evolution.  Develop a novel statistical method, based on the HOD, to solve for this mapping by jointing fitting the galaxy clustering and gg-lensing measured from SDSS.  The method, called the iHOD model, extracts maximum information from the survey by including ~80% more galaxies than the traditional HOD methods, and takes into account the incompleteness of the stellar mass samples in a statistically consistent manner.  The derived stellar-to-halo mass relation not only explains the clustering and lensing of SDSS galaxies over almost four decades in stellar mass, but also successfully predicts the stellar mass functions observed in SDSS.  Due to its capability of modeling significantly more galaxies, the iHOD is able to break the degeneracy between the logarithmic scatter in the stellar mass at fixed halo mass and the slope of the stellar-to-halo mass relation at high mass end, without the need to assume a strong prior on the scatter in the stellar mass at fixed halo mass and/or use the stellar mass function as input.  Detect a decline of the scatter with halo mass, from 0.22 dex at below 1e12 Msun to 0.18 dex at 1e14 Msun.  The model also enables stringent constraints on the satellite stellar mass functions at fixed halo mass, predicting departure from the Schechter functional form in high mass haloes.  The iHOD model can be easily applied to existing and future spectroscopic datasets, greatly improving the statistical constraint on the stellar-to-halo mass relation compared to the traditional HOD methods within the same survey.


1505.02887
A weak lensing analysis of the PLCK G100.2-30.4 cluster
Radovich et al

Present a mass estimate of the Planck-discovered cluster PLCK G100.2-30.4, derived from a weak lensing analysis of deep SUBARU griz images.  Perform a careful selection of the background galaxies using the multi-band imaging data, and undertake the weak lensing analysis on the deep (1hr) r-band image.  The shape measurement is based on the KSB algorithm; adopt the PSFEx software to model the PSF across the field and correct for this in the shape measurement.  The weak lensing analysis is validated through extensive image simulations.  Compare the resulting WL mass profile and total mass estimate to those obtained from the re-analysis of XMM-Newton observations, derived under the hypothesis of hydrostatic equilibrium.  The total integrated mass profiles are in remarkably good agreement, agreeing within 1 sigma across their common radial range.  A mass M500~7e14 Msun is derived for the cluster from the WL analysis.  Comparing this value to that obtained from the reanalysis of XMM-Newton data, obtain a bias factor of (1-b)=0.8±0.1.  This is compatible within 1 sigma with the value of (1-b) obtained by Planck collaboration XXIV from their calibration of the bias factor using newly-available WL reconstructed masses.


1505.03124
Galaxy shapes and alignments in the MassiveBlack-II hydrodynamic and dark matter-only simulations
Tenneti, Mandelbaum, Matteo, Kiessling, Khandai

Compare the shapes and IA of galaxies in the MB-II cosmological hydro sim (MBII) to those in the DM-only (DMO) sim performed with the same volume (100 Mpc/h)^3, cosmo parameters, and ICs.  Understanding the impact of baryonic physics on galaxy shapes and alignments and their relation to the DM distribution should prove useful to map the IAs of galaxies from hydrodynamic to DM-only sims.  Find that DM subhalos are typically rounder in MBII, and the shapes of stellar matter in low mass galaxies are more misaligned with the shapes of the DM of the corresponding sub haloes in the DMO sim.  At z=0.06, the fractional difference in the mean misalignment angle between MBII and DMO sims varies from ~28%-12% in the mass range 1e10.8-6e14 Msun/h.  Study the DM halo shapes and alignments as a function of radius, and find that while galaxies in MBII are more aligned with the inner parts of their DM sub haloes, there is no radial trend in their alignments with the corresponding subhalo in the DMO sim.  This result highlights the importance of baryonic physics in determining the alignment of the galaxy with respect to the inner parts of the halo.  Finally, compare the ellipticity-direction (ED) correlation for galaxies to that for DM haloes, fining that it is suppressed on all scales by stellar-DM misalignment.  In the projected shape-density correlation (w_delta+), which includes ellipticity weighting, this effect is partially canceled by the higher mean ellipticities of the stellar component, but differences of order 30-40% remain on scales >1 Mpc over a range of sub halo masses, with scale-dependent effects below 1 Mpc.