A SPECTROSCOPIC SURVEY OF THE GALAXY CLUSTER CL-1358+62 AT Z=0.328

We present a spectroscopic survey of the rich X-ray-selected galaxy cl uster CL 1358+6245 at z = 0.328. When our 173 new multislit spectra of cluster galaxies are combined with data from the literature, we produ ce a catalog of 232 cluster members in a region 10' x 11' (3.5 Mpc x 3 .8 Mpc) surrounding the brightest cluster galaxy. These data are used to study the structure and dynamics of the cluster and to examine the radial and velocity distributions as a function of spectral type. We c lassify the spectral types of the cluster members according to the str engths of the Balmer absorption lines (H delta, H gamma, and H beta) a nd the [O II] 3727 Angstrom emission line. We derive a mean redshift o f z = 0.3283 +/- 0.0003 and a velocity dispersion of 1027(-45)(+51) km s(-1) for the 232 cluster members. However, the cluster velocity dist ribution is non-Gaussian, and we identify at least two subgroups with 10-20 members and dispersions of <400 km s(-1). The fraction of spectr oscopically active galaxies (poststarburst and emission-line) in the c ore of the velocity distribution (within 0.6 sigma of the mean cluster velocity) is 16% +/- 4%, rising to 32% +/- 7% for galaxies in the tai ls of the velocity distribution (2.0 sigma from the mean cluster veloc ity). In total, the cluster is composed of 19% +/- 3% emission-line an d 5% +/- 1% poststarburst galaxies. The velocity dispersion of the pos tstarburst galaxies is close to 2(1/2) times that of the absorption-li ne galaxies, consistent with free-fall accretion of the poststarburst galaxies. The changing mix of galaxy spectral types as a function of l ocal galaxy density (or distance from the cluster center) in CL 1358+6 2 is similar to what is observed in nearby rich clusters. The percenta ge of emission-line galaxies increases steadily with radius from 9% +/ - 3% within a radius of r(p) < 0.7 Mpc to 41% +/- 9% in our outermost radial bin at similar to 1.7 Mpc. The percentage of absorption-line ga laxies falls from 84% +/- 9% to 59% +/- 11% over the same radial inter vals. These results are consistent with the idea that the cluster grow s through the accretion of late-type field galaxies, a fraction of whi ch are transformed into poststarburst galaxies during the accretion ev ent. Our high-S/N spectra of the ''E + A'' galaxies allow a detailed c omparison with spectra of nearby merging and strongly interacting gala xy systems. We find that nearby mergers have stronger [O II] 3727 Angs trom emission ([O II] EW > 5 Angstrom) than that observed for our E A galaxies. This implies either that the E + A galaxies in CL 1358 + 6 2 were not formed through major mergers, or that if they were formed v ia merging, their gas supply was quickly depleted, possibly by the int racluster medium.