2004AJ....128.2631W

SDSS J1004+4112 is an unprecedented object. It looks much like several quadruple quasars lensed by individual galaxies, only it is ∼10 times larger and the lens is a cluster dominated by dark matter. We present free-form reconstructions of the lens using recently developed methods. The projected cluster mass profile is consistent with being shallow, r^–0.3 to r^–0.5, and can be fitted with either a Navarro-Frenk-White or a flat-cored three-dimensional mass distribution. However, we cannot rule out projected profiles as steep as r^–1.3. The projected mass within 100 kpc is well constrained as (5±1)x10¹³ M_☉, consistent with previous simpler models. Unlike previous work, however, we are able to detect structures in the lens associated with cluster galaxies. We estimate the mass associated with these galaxies and show that they contribute not more than about 10% of the total cluster mass within 100 kpc. Typical galaxy masses, combined with typical luminosities, yield a rough estimate of their mass-to-light ratio, which is in the single digits. Finally, we discuss implications for time-delay measurements in this system, and possibilities for a partial Einstein ring.