LATEX style emulateapjTHE STAR FORMATION HISTORIES OF GALAXIES IN DISTANT CLUSTERS 1

We present a detailed analysis of the spectroscopic catalog of galaxies in 10 distant clusters from Dressler et al. (1999, D99). We investigate the nature of the diierent spectral classes deened by D99 including star forming, post{starburst 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 search for the progenitors of the numerous post{starburst galaxies. The comparison of the spectra of the distant galaxy populations with samples drawn from the local Universe leads us to identify a signiicant population of dust{ enshrouded starburst galaxies, showing both strong Balmer absorption and relatively modest OII] emission, that we believe are the most likely progenitors of the post{starburst population. We present the diierences between the eld and cluster galaxies at z = 0:4{0.5. We then compare the spectral and the morphological properties of the distant cluster galaxies, exploring the connection between the quenching of star formation inferred from the spectra and the strong evolution of the S0 population discussed by Dressler et al. (1997). We conclude that either two diierent timescales and/or two diierent physical processes are responsible for the spectral and the morphological transformation. 1. INTRODUCTION Of all the environments explored locally, the dense, concentrated cores of rich clusters are highly conspicuous for their lack of star-forming galaxies. Thus it came as a surprise when Butcher & Oemler (1978; see also Butcher & Oemler 1984) discovered a population of blue, possibly star-forming, galaxies