The Evolution of Galaxies in Compact Groups

We present the analysis of the spectra of 62 galaxies in 15 compact groups.The galaxies were classified in four activity classes: galaxies withoutemission, starburst nucleus galaxies (SBNGs), luminous AGNs and low-luminosityAGNs (LLAGNs). The star formation in the HCG starbursts is more intense than in normalspirals, but comparable to those in the field SBNGs. Their mean gas metallicityis solar and they do not follow the metallicity-luminosity relation traced bythe early-type SBNGs in the field, suggesting that most of them are late-typeSBNGs. This morphology preference coupled to the observation that the HCGstarbursts are predominantly in the halo of the groups is consistent with theidea that compact groups are embedded in sparser structures. The stellar metallicities of the non starburst galaxies are relatively highfor their luminosities. In these galaxies the equivalent widths of the metalabsorption lines are slightly narrower than normal while the Balmer absorptionlines are relatively strong. All these galaxies could be ``post-starburst'' atan advanced stage of evolution. Our observations are supporting a scenario where the core of the groups areslowly collapsing evolved systems embedded in more extended structures (Ribeiroet al. 1998). In the core of the groups, the interactions were more frequentand the galaxies evolved at a more rapid rate than in their halos.Comment: 36 pages, 10 encapsulated postscript figures. to appear in ApJ, October 20, 1998 issue, Vol. 506 #