2010ApJ...724..714H

We have measured velocity dispersions (σ) 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 δ(σ) ∼ 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 ^{sstarf} galaxy at z ∼ 1, unlike most previous z ∼ 1 cluster samples which are complete only for the massive cluster members (>10¹¹ M_☉). 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-σ relation and M/L_B-σ relations; measuring evolution at a fixed σ should minimize the impact of structural evolution found in other work. The M/L_B at fixed σ evolves by Δlog₁₀M/L_B = -0.50±0.03 between z = 0.83 and z = 0.02 or dlog₁₀M/L_B= -0.60 ± 0.04 dz, and we find Δ(U - V)_z= -0.24±0.02 mag at fixed σ in the rest frame, matching the expected evolution in M/L_B within 2.25 standard deviations. The implied formation redshift from both the color and M/L_B evolution is z_{sstarf}= 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_{sstarf} 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-σ and color-σ relations imply that the formation epoch depends weakly on mass, ranging from z_{sstarf}= 2.3^+1.3_–0.3 at σ = 300 km/s to z_{sstarf}= 1.7^+0.3_–0.2 at σ = 160 km/s and implies that the initial mass function similarly varies slowly with galaxy mass.