A Spectroscopic Redshift for the Cl 0024+16 Multiple Arc System: Implications for the Central Mass Distribution

We present a spectroscopic redshift of z = 1.675 for the well-known multiply lensed system of arcs seen in the z = 0.39 cluster Cl 0024+16. In contrast to earlier work, we find that the lensed images are accurately reproduced by a projected mass distribution which traces the locations of the brightest cluster elliptical galaxies, suggesting that the most significant minima of the cluster potential are not dynamically erased. The averaged mass profile is shallow and consistent with predictions of recent numerical simulations. The source redshift enables us to determine an enclosed cluster mass of M(<100 kpc h-1) = 1.11 ± 0.03 × 1014 h-1 M☉ (Ω = 1) and a mass-to-light ratio of M/LB(<100 kpc h-1) = 320 ± 30 h (M/LB)☉ (virtually independent of curvature), after correction for passive stellar evolution. The arc spectrum contains many ionized absorption lines and closely resembles that of the local Wolf-Rayet galaxy NGC 4217. Our lens model predicts a high magnification (≃20) for each image and identifies a new pair of multiple images of a galaxy at a predicted redshift of z = 1.3.