The Sloan Lens ACS Survey. IV. The Mass Density Profile of Early‐Type Galaxies out to 100 Effective Radii (original) (raw)

2007, The Astrophysical Journal

We present a weak gravitational lensing analysis of 22 early-type (strong) lens galaxies, based on deep Hubble Space Telescope images obtained as part of the Sloan Lens ACS Survey. Using advanced techniques to control systematic uncertainties related to the variable point spread function and charge transfer efficiency of the Advanced Camera for Surveys (ACS), we show that weak lensing signal is detected out to the edge of the Wide Field Camera ( 300 h −1 kpc at the mean lens redshift z = 0.2). We analyze blank control fields from the COSMOS survey in the same manner, inferring that the residual systematic uncertainty in the tangential shear is less than 0.3%. A joint strong and weak lensing analysis shows that the average total mass density profile is consistent with isothermal (i.e. ρ ∝ r −2 ) over two decades in radius (3-300 h −1 kpc, approximately 1-100 effective radii). This finding extends by over an order of magnitude in radius previous results, based on strong lensing and/or stellar dynamics, that luminous and dark component "conspire" to form an isothermal mass distribution. In order to disentangle the contributions of luminous and dark matter, we fit a twocomponent mass model (de Vaucouleurs + Navarro Frenk & White) to the weak and strong lensing constraints. It provides a good fit to the data with only two free parameters; i) the average stellar mass-to-light ratio M * /L V = 4.48±0.46 hM ⊙ /L ⊙ (at z = 0.2), in agreement with that expected for an old stellar population; ii) the average virial mass-to-light ratio M vir /L V = 246 +101 −87 hM ⊙ /L ⊙ . Taking into account the scatter in the mass-luminosity relation, this latter result is in good agreement with semi-analytical models of massive galaxies formation. The dark matter fraction inside the sphere of radius the effective radius is found to be 27±4%. Our results are consistent with galaxy-galaxy lensing studies of early-type galaxies that are not strong lenses, in the region of overlap (30-300 h −1 kpc). Thus, within the uncertainties, our results are representative of early-type galaxies in general.

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