The Masses and Shapes of Dark Matter Halos from Galaxy‐Galaxy Lensing in the CFHT Legacy Survey

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 deg 2 of i ' data. From these data, we estimate the average velocity dispersion for an L * galaxy at a redshift of 0.3 to be 137 ± 11 km s -1 , with a virial mass, M 200 , of (1.1 ± 0.2) × 10 12 h -1 M ☉ and a rest-frame mass-to-light ratio of 173 ± 34 h M ☉ / L . We also investigate various possible sources of systematic error in detail. In addition, we separate our lens sample into two subsamples, divided by apparent magnitude and thus average redshift. From these early data we do not detect significant evolution in galaxy dark matter halo mass-to-light ratios at redshifts from 0.45 to 0.27. Finally, we test for nonspherical galaxy dark matter halos. Our results favor a dark matter halo with an ellipticity of ~0.3 at the 2 σ level when averaged over all galaxies. If the sample of foreground lens galaxies is selected to favor elliptical galaxies, the mean halo ellipticity and significance of this result increase.