The star formation histories of galaxies in distant clusters

We present a detailed analysis of the spectroscopic catalog of galaxies in 10 distant clusters from Dressier et al. We investigate the nature of the d ifferent spectral classes defined by Dressier et al., including star-formin g, poststarburst, and passive galaxy populations, and reproduce their basic properties using our spectral synthesis model. We attempt to identify the evolutionary pathways between the various spectral classes in order to sear ch for the progenitors of the numerous poststarburst galaxies. The comparis on of the spectra of the distant galaxy populations with samples drawn from the local universe leads us to identify a significant population of dust-e nshrouded starburst galaxies, showing both strong Balmer absorption and rel atively modest [O II] emission, that we believe are the most likely progeni tors of the poststarburst population. We present the differences between th e field and cluster galaxies at z = 0.4-0.5. We then compare the spectral a nd morphological properties of the distant cluster galaxies, exploring the connection between the quenching of star formation inferred from the spectr a and the strong evolution of the S0 population discussed by Dressier et al . We conclude that either two different timescales and/or two different phy sical processes are responsible for the spectral and morphological transfor mation.