Models of the giant quadruple quasar SDSS J1004+4112
  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...-0.5}, and can be fit with either an NFW or a flat-cored 3 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 10^{13}M_sun, 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. 
Liliya L.R. Williams (U Minnesota) Prasenjit Saha (QMW London)