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 cluster CL 1358+6245 at z = 0.328. When our 173 new multislit spectra of cluster galaxies are combined with data from the literature, we produce 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 classify the spectral types of the cluster members according to the strengths of the Balmer absorption lines (H delta, H gamma, and H beta) and the [O II] 3727 Angstrom emission line.

We derive a mean redshift of 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 distribution is non-Gaussian, and we identify at least two subgroups with 10-20 members and dispersions of

The changing mix of galaxy spectral types as a function of local galaxy density (or distance from the cluster center) in CL 1358+62 is similar to what is observed in nearby rich clusters. The percentage 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 galaxies falls from 84% +/- 9% to 59% +/- 11% over the same radial intervals. These results are consistent with the idea that the cluster grows through the accretion of late-type field galaxies, a fraction of which are transformed into poststarburst galaxies during the accretion event.

Our high-S/N spectra of the "E + A" galaxies allow a detailed comparison with spectra of nearby merging and strongly interacting galaxy systems. We find that nearby mergers have stronger [O II] 3727 Angstrom 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 + 62 were not formed through major mergers, or that if they were formed via merging, their gas supply was quickly depleted, possibly by the intracluster medium.