Day 840

Wednesday.

1502.06604
Can we use weak lensing to measure total mass profiles of galaxies on 20 kilo parsec scales?
Kobayashi, Leauthaud, More, Okabe, Laigle, Rhodes, Takeuchi

Current constraints on DM density profiles from WL are typically limited to radial scales greater than 50-100 kpc.  In this paper, explore the possibility of probing the very inner regions of galaxy/halo density profiles by measuring stacked WL on scales of only a few tens of kpc.  The forecasts focus on  scales smaller than the equality radius (Req) where the stellar component and the DM component contribute equally to the lensing signal.  Compute the evolution of Req as a function of lens stellar mass and redshift and show that Req=7-34 kpc for galaxies with the stellar mass of 1e9.5-11.5 Msun.  Unbiased shear measurement will be challenging on these scales.  Introduce a simple metric to quantify how many source galaxies overlap with their neighbors and for which shear measurement will be challenging.  Rejecting source galaxies with close-by companions results in about a 20% decrease in the overall source density.  Despite this decrease, show that Euclid and WFIRST will be able to constrain galaxy/halo density profiles at Req with S/N >20 for M* >1e10 Msun.  WL measurements at Req, in combination with stellar kinematics on small scales, will be a powerful means by which to constrain both the inner slope of the DM density profile as well as the mass and z dependence of the stellar IMF.  


1502.06614
The galaxy - dark matter halo connection: which galaxy properties are correlated with the host halo mass?
Contreras, Baugh, Norberg, Padilla

Demonstrate how the properties of a galaxy depend on the mass of its host dark matter sub halo, using two independent models of galaxy formation.  For the cases of stellar mass and BH mass, the median property value displays a monotonic dependence on sub halo mass.  The slope of the relation changes for sub halo masses for which heating by AGN becomes important.  The median property values are predicted to be remarkably similar for central and satellite galaxies.  The two models predict considerable scatter around the median property value, though the size of the scatter is model  dependent.  There is only modest evolution with z in the median galaxy property at a fixed sub halo mass.  Properties such as cold gas mass and SFR, however, are predicted to have a complex dependence on sub halo mass.  In these cases sub halo mass is not a good indicator of the value of the galaxy property.  Illustrate how the predictions in the galaxy property - sub halo mass plane differ from the assumptions made in empirical models of galaxy clustering by reconstruction the model output using a sub halo abundance matching scheme.  In its simplest form, abundance matching generally does not reproduce the clustering predicted by the models, typically resulting in an overproduction of the clustering signal.  Show how the basic abundance matching scheme can be extended to reproduce the model predictions more faithfully, which has implications for the analysis of galaxy clustering, particularly for low abundance samples.