Spectroscopic signatures of galaxy evolution in Cl0024+16 at z∼ 0.4

We report the first results from a panoramic spectroscopic survey of galaxies in the rich cluster Cl0024+1654 (z≃ 0.4). Using HST imaging we examine the properties of early-types as a function of cluster radius. At all cluster radii, our sample lies on a self-consistent Fundamental Plane whose zero point implies evolution since z=0 corresponding to Δ[log (M/L_V)] = 0.14 ± 0.06, an overall trend consistent with previous work. Using diagnostic [O II] emission and Balmer absorption lines, we locate a population of intrinsically faint galaxies at 1-2.4 Mpc radius undergoing a period of star formation. The luminosity-dependent radial trends are suggestive of the gradual quenching of star formation for infalling galaxies. We discuss physical mechanisms that may be responsible for this environmental evolution.