The Nature of E+A Galaxies in Intermediate‐Redshift Clusters

[Abridged] Combining HST/WFPC2 mosaics with extensive ground-basedspectroscopy, we study the nature of E+A galaxies in three intermediateredshift clusters (z=0.33, 0.58, & 0.83). From a sample of ~500 confirmedcluster members, we isolate 46 E+A candidates to determine the E+A fraction andstudy their physical properties. We find E+A's comprise a non-negligiblecomponent (~7-13%) of the cluster population at these redshifts, and theirdiverse nature indicates a heterogeneous parent population. Cluster E+A's spanthe range in Hubble type and cover a wide range in luminosity, internalvelocity dispersion, and half-light radius. From their velocity dispersions andhalf-light radii, we infer that the descendants of E+A's in our highestredshift cluster are massive early-type galaxies. We find a decrease in thecharacteristic E+A mass similar to the decrease in luminosity of rapidlystar-forming field galaxies since z~1, i.e. galaxy ``down-sizing.'' Inaddition, we argue our statistics imply that >30% of the E-S0 members haveundergone an E+A phase; the true fraction could be 100% if the effects of E+Adown-sizing, an increasing E+A fraction with redshift, and the conversion ofspirals into early-types are also considered. Thus, the E+A phase may indeed bean important stage in the transformation of star-forming galaxies intoearly-type cluster members.