The Masses and Shapes of Dark Matter Halos from Galaxy-Galaxy Lensing in the CFHTLS

TL;DR

This study uses early CFHTLS data to measure galaxy dark matter halo properties through weak lensing, finding typical halo masses, mass-to-light ratios, and evidence for non-spherical halo shapes.

Contribution

First galaxy-galaxy weak lensing analysis with CFHTLS data, providing measurements of halo masses, shapes, and testing for evolution and ellipticity.

Findings

Average velocity dispersion of 137 km/s for L* galaxies at z=0.3

Virial mass M_{200} of 1.1 x 10^{12} h^{-1} Msun

Dark matter halos have an ellipticity of ~0.3

Abstract

We present the first galaxy-galaxy weak lensing results using early data from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). These results are based on ~22 sq. deg. of i' data. From this data, we estimate the average velocity dispersion for an L* galaxy at a redshift of 0.3 to be 137 +- 11 km/s, with a virial mass, M_{200}, of 1.1 +- 0.2 \times 10^{12} h^{-1} Msun and a rest frame R-band mass-to-light ratio of 173 +- 34 h Msun/Lsun. We also investigate various possible sources of systematic error in detail. Additionally, we separate our lens sample into two sub-samples, divided by apparent magnitude, thus average redshift. From this early data we do not detect significant evolution in galaxy dark matter halo mass-to-light ratios from a redshift of 0.45 to 0.27. Finally, we test for non-spherical galaxy dark matter halos. Our results favor a dark matter halo with an ellipticity of ~0.3 at the 2-sigma level when averaged over all galaxies. If the sample of foreground lens galaxies is selected to favor ellipticals, the mean halo ellipticity and significance of this result increase.