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

We present a weak-lensing analysis of 22 early-type (strong) lens galaxies, based on deep HST images obtained as part of the Sloan Lens ACS Survey. Using advanced techniques to control systematic uncertainties, we show that weak-lensing signal is detected out to 300 h 1 kpc (at the mean lens redshift z 0: 2). We analyze blank control fields from COSMOS 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. , / r 2) over two decades in radius (3Y300 h 1 kpc, approximately 1Y100 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 components ''conspire'' to form an isothermal mass distribution. In order to disentangle the contributions of luminous and dark matter, we fit a two-component mass model (de Vaucouleurs+NFW) to the weak-and strong-lensing constraints. It provides a good fit to the data with only two free parameters: (1) the average stellar mass-to-light ratio M /L V 4: 48 AE 0: 46 h M L 1