M/LB AND COLOR EVOLUTION FOR A DEEP SAMPLE OF M* CLUSTER GALAXIES AT z ∼ 1: THE FORMATION EPOCH AND THE TILT OF THE FUNDAMENTAL PLANE

We have measured velocity dispersions (sigma) for a sample of 36 galaxies with J < 21.2 or M-r < -20.6 mag in MS 1054-03, a massive cluster of galaxies at z = 0.83. Our data are of uniformly high quality down to our selection limit, our 16 hr exposures typically yielding errors of only delta(sigma) similar to 10% for L* and fainter galaxies. By combining our measurements with data from the literature, we have 53 cluster galaxies with measured dispersions, and HST/ACS-derived sizes, colors and surface brightness. This sample is complete for the typical L-star galaxy at z similar to 1, unlike most previous z similar to 1 cluster samples which are complete only for the massive cluster members (>10(11) M-circle dot). We find no evidence for a change in the tilt of the fundamental plane (FP). Nor do we find evidence for evolution in the slope of the color-sigma relation and M/L-B-sigma relations; measuring evolution at a fixed sigma should minimize the impact of structural evolution found in other work. The M/L-B at fixed sigma evolves by Delta log(10) M/L-B = -0.50 +/- 0.03 between z = 0.83 and z = 0.02 or d log(10) M/L-B = -0.60 +/- 0.04 dz, and we find Delta(U-V)(z) = -0.24 +/- 0.02 mag at fixed sigma in the rest frame, matching the expected evolution in M/LB within 2.25 standard deviations. The implied formation redshift from both the color and M/L-B evolution is z(star) = 2.0+/-0.2+/-0.3(sys), during the epoch in which the cosmic star formation activity peaked, with the systematic uncertainty showing the dependence of z(star) on the assumptions we make about the stellar populations. The lack of evolution in either the tilt of the FP or in the M/L-sigma and color-sigma relations imply that the formation epoch depends weakly on mass, ranging from z(star) = 2.3(-0.3)(+1.3) at sigma = 300 km s(-1) to z(star) = 1.7(-0.2)(+0.3) at sigma = 160 km s(-1) and implies that the initial mass function similarly varies slowly with galaxy mass.