Cluster of compact galaxies Zw Cl 0152 + 33

Redshifts have been determined for 14 seventeenth-magnitude, mostly red, compact galaxies which form an elongated system at the center of the cluster Zw Cl 0152+33. This cluster was discovered by Zwicky to contain a vast preponderance of compact galaxies and, in this respect, is very unusuaL The mean redshift is 26,304 km s ' and the apparent distance modulus of the cluster is (`n - M) = 38.2. The brightest galaxy in the cluster, which is a compact galaxy according to Zwicky, has Mp = -21.2. All the observed galaxies except one have late-type absorption spectra; the remaining galaxy is blue and has an emission-line spectrum. It is argued that the galaxies in the elongated system do not form a linear chain, but are in a flattened system seen nearly edge-on. An application of the virial theorem is complicated by the fact that the galaxies on the outer parts of the region considered have a higher velocity dispersion <r than those in the center. As a result we find that the center of the cluster is probably a bound system while the outer members are escaping from the cluster on a timescale of about 10 years. This is smaller by a factor of 100 than the estimated dynamical relaxation time in the cluster; as a result the overall dynamics of the cluster are not understood.