Date Published:

Abstract:

We study the recently discovered gravitational lens SDSS J1004+4112, thefirst quasar lensed by a cluster of galaxies. It consists of four imageswith a maximum separation of 14.62". The system was selected from thephotometric data of the Sloan Digital Sky Survey (SDSS) and has beenconfirmed as a lensed quasar at z=1.734 on the basis of deep imaging andspectroscopic follow-up observations. We present color-magnituderelations for galaxies near the lens plus spectroscopy of three centralcluster members, which unambiguously confirm that a cluster at z=0.68 isresponsible for the large image separation. We find a wide range of lensmodels consistent with the data, and despite considerable diversity theysuggest four general conclusions: (1) the brightest cluster galaxy andthe center of the cluster potential well appear to be offset by severalkiloparsecs; (2) the cluster mass distribution must be elongated in thenorth-south direction, which is consistent with the observeddistribution of cluster galaxies; (3) the inference of a large tidalshear (~0.2) suggests significant substructure in the cluster; and (4)enormous uncertainty in the predicted time delays between the imagesmeans that measuring the delays would greatly improve constraints on themodels. We also compute the probability of such large-separation lensingin the SDSS quasar sample on the basis of the cold dark matter model.The lack of large-separation lenses in previous surveys and thediscovery of one in SDSS together imply a mass fluctuation normalization

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