The evolution of galaxies in compact groups

We present an analysis of the spectra of 62 galaxies in 15 compact groups. The galaxies are classified into four activity classes: galaxies without em ission, starburst galaxies, luminous AGNs (Seyfert and LINERs), and low-lum inosity AGNs (LLAGNs). The star formation in the Hickson compact group (HCG ) starbursts is more intense than in normal spirals, but comparable to that observed in starburst-nucleus galaxies (SBNGs) in the held. In general, th e HCG starbursts have mean solar gas metallicity and do not follow the meta llicity-luminosity relation traced by the early-type SBNGs in the field, su ggesting that most of them are late-type SBNGs. This morphology preference, coupled with the observation that the HCG starbursts are predominantly loc ated in the halos of the groups, is consistent with the idea that compact g roups are embedded in sparser structures. The stellar metallicities of the nonstarburst galaxies are comparable to those observed in normal galaxies w ith similar morphologies, but are relatively high for their luminosities. I n these galaxies, the metal absorption line equivalent widths are slightly narrower than normal, while the Balmer absorption lines are relatively stro ng. All these observations suggest the presence of a population of intermed iate-age stars. These galaxies could be poststarburst, but at a very advanc ed stage of evolution, the last bursts having happened more than 2 Gyr in t he past. Our observations support a scenario in which the cores of the grou ps are slowly collapsing evolved systems embedded in more extended structur es. In the cores of the groups, the interactions were more frequent and the galaxies evolved at a more rapid rate than in their halos.