Properties of Galaxy Dark Matter Halos from Weak Lensing

Abstract

We present the results of a study of weak lensing by galaxies based on 45.5 deg 2 of R C band 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 C < 24.We 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 , suggesting that the dark matter halos are somewhat rounder than the light distribution. The fact that we detect a significant flattening implies that the halos are well aligned with the light distribution. Given the average ellipticity of the lenses, this implies a halo ellipticity of e halo = 0.33 +0.07 −0.09 , in fair agreement with results from numerical simulations of CDM. We note that this result is formally a lower limit to the flattening, since the measurements imply a larger flattening if the halos are not aligned with the light distribution. Alternative theories of gravity (without dark matter) predict an isotropic lensing signal, which is excluded with 99.5% confidence. Hence, our results provide strong support for the existence of dark matter.We also study the average mass profile around the lenses, using a maximum likelihood analysis. We consider two models for the halo mass profile: a truncated isothermal sphere (TIS) and an NFW profile. We adopt observationally motivated scaling relations between the lens luminosity and the velocity dispersion and the extent of the halo. The TIS model yields a best fit velocity dispersion of σ = 136±5±3 km/s (all errors are 68% confidence limits; the first error bar indicates the statistical uncertainty, whereas the second error bar indicates the systematic error) and a truncation radius s = 185 +30 −28 h −1 kpc for a galaxy with a fiducial luminosity of L B = 10 10 h −2 L B⊙ (under the assumption that the luminosity does not evolve with redshift). Alternatively, the best fit NFW model yields a mass M 200 = (8.4 ± 0.7 ± 0.4) × 10 11 h −1 M ⊙ and a scale radius r s = 16.2 +3.6 −2.9 h −1 kpc. This value for the scale radius is in excellent agreement with predictions from numerical simulations for a halo of this mass.

Dependence of GAMA galaxy halo masses on the cosmic web environment from 100 deg2of KiDS weak lensing data

“…More specifically, we use galaxy-galaxy lensing (GGL; see e.g. Brainerd, Blandford & Smail 1996;Hoekstra, Yee & Gladders 2004;Mandelbaum et al 2006): the coherent tangential distortion of background galaxy images due to the gravitational deflection of light by the mass of a sample of foreground galaxies and their haloes. To select foreground galaxies, we use the spectroscopic Galaxy And Mass Assembly survey (Driver et al 2011), whereas the images of the background galaxies are taken from the photometric KiloDegree Survey (de Jong et al 2013).…”

Weak lensing, dark matter and dark energy

“…This method goes under the name of "galaxy-galaxy lensing" [2,36,37,38,39], and essentially measures the galaxyshear correlation function across the sky. Galaxy-galaxy lensing measures the surface mass density contrast ∆Σ(R)…”

Weak lensing constraints on the dark matter haloes of early type galaxies

“…Brainerd, Blandford & Smail 1996;Hudson et al 1998;Hoekstra et al 2004). In particular, Hoekstra et al (2004) report the detection of finite truncation radii based on the imaging data from the Red-Sequence Cluster Survey.…”

“…Brainerd, Blandford & Smail 1996;Hudson et al 1998;Hoekstra et al 2004). In particular, Hoekstra et al (2004) report the detection of finite truncation radii based on the imaging data from the Red-Sequence Cluster Survey. Using a truncated isothermal sphere to model the mass in galaxy haloes, they find a best-fit central velocity dispersion for an L * galaxy of σ = 136 ± 5 kms −1 (68% confidence limits) and a truncation radius of 185 ± 30 kpc.…”