Properties of galaxy dark matter halos from weak lensing
Abstract
We present the results of a study of weak lensing by galaxies based on imaging data from the Red-Sequence Cluster Survey (RCS). We define a sample of lenses with 19.5<R_C<21, and a sample of background galaxies with 21.5<R<24. We consider a truncated isothermal sphere (TIS) and an NFW profile. We constrain the power law scaling relations between the $B$-band luminosity and the velocity dispersion (or rotation velocity) and the size of the halo. The inferred velocity dispersion is in agreement with observed luminosity-line-width relations. The best fit NFW model yields a mass M_{200}=(8.8+-0.7)x 10^{11} h^{-1} Msun and a scale radius r_s=16.7^{+3.7}_{-3.0} h^{-1} kpc. This value for the scale radius is in excellent agreement with predictions from numerical simulations for a halo of this mass. Having constrained the virial mass and scaling relations, we can convert the observed luminosity function into a mass function, and estimate the matter density of the universe, for which we obtain \Omega_m=0.30^{+0.13}_{-0.08}. We also present the first weak lensing detection of the flattening of galaxy dark matter halos. We use a simple model in which the ellipticity of the halo is f times the observed ellipticity of the lens. We find a best fit value of f=0.77^{+0.18}_{-0.21}. The fact that we detect a significant flattening implies that the halos are aligned with the light distribution. Given the average ellipticity of the lenses, this implies a halo ellipticity of e_halo=0.20^{+0.04}_{-0.05}, in fair agreement with results from numerical simulations of CDM. This result provides strong support for the existence of dark matter, as an isotropic lensing signal is excluded with 99.5% confidence.Keywords
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