We present the results of the spectral classiÐcation of the 82 brightest galaxies in a sample of 17 compact groups. We verify that the active galactic nuclei (AGNs) are preferentially located in the most early-type and luminous galaxies of the groups, as is usually observed in the Ðeld. But these AGNs also appear to be systematically concentrated toward the central parts of the groups. Our observations suggest a correlation between activity types, morphologies, and densities of galaxies in the compact groups. This is consistent with a scenario in which galaxies of compact groups evolve by interacting with their environment and are currently in a quiet phase of their activity.

Using a sample of 91 galaxies distributed over 27 compact groups (CGs) of galaxies, we define an index that allows us to quantify their level of activity due to an active galactic nucleus (AGN) or star formation. By combining the mean activity index with the mean morphological type of the galaxies in a group, we are able to quantify the evolutionary state of the groups. We find that they span an evolutionary sequence that correlates with the spatial configuration of the galaxies in the CG. We distinguish three main configuration types: A, B, and C. Type A CGs show predominantly low velocity dispersions and are rich in late-type spirals that show active star formation or harbor an AGN. Type B groups have intermediate velocity dispersions and contain a large fraction of interacting or merging galaxies. Type C comprises CGs with high velocity dispersions, which are dominated by elliptical galaxies that show no activity. We suggest that evolution proceeds A j B j C. Mapping the groups with different evolution levels in a diagram of radius versus velocity dispersion does not reveal the pattern expected based on the conventional fast merger model for CGs, which predicts a direct relation between these two parameters. Instead, we observe a trend contrary to expectation: the evolutionary state of a group increases with velocity dispersion. This trend seems to be related to the masses of the structures in which CGs are embedded. In general, the evolutionary state of a group increases with the mass of the structure. This suggests either that galaxies evolve more rapidly in massive structures or that the formation of CGs embedded in massive structures predated the formation of CGs associated with lower mass systems. Our observations are consistent with the structure formation predicted by the CDM model (or ÃCDM), only if the formation of galaxies is a biased process.

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We present the results of the classification of spectral activity types for 193 galaxies from a new sample of 49 compact groups of galaxies in the southern hemisphere (SCGs). The SCGs is a new sample of compact groups selected in automated fashion from a digitized galaxy catalogue, covering an area of ∼ 5200 sq deg around the South Galactic Pole. It is complete up to m∼ 14.5 in

We have conducted a new spectroscopic survey to characterize the nature of nuclear activity in Hickson Compact Groups (HCGs) galaxies and establish its frequency. We have obtained new intermediate resolution optical spectroscopy for 200 member-galaxies and corrected for underlying stellar population contamination using galaxy templates. Spectra for 11 additional galaxies have been acquired from the ESO and 6dF public archives and emission line ratios have been taken from the literature for 59 galaxies more. Here we present the results of our classification of the nuclear activity for 270 member-galaxies, which belong to a well defined sample of 64 HCGs. We found a large fraction of galaxies, 63%, with emission lines. Using standard diagnostic diagrams, 45% of the emission line galaxies were classified as pure AGNs, 23% as Transition Objects (TOs) and 32% as Star Forming Nuclei (SFNs). In the HCGs, the AGN activity appears as the most frequent activity type. Adopting the interpretation that in TOs a Low Luminosity AGN coexists with circumnuclear star formation, the fraction of galaxies with an AGN could rise to 42% of the whole sample. The low frequency (20%) of SFNs confirms that there is no star formation enhancement in HCGs. After extinction correction we found a median AGN Hα luminosity of 7.1×10 39 erg s −1 , which implies that AGNs in HCG have a characteristically low luminosity. This result added to the fact, that there is an almost complete absence of Broad Line AGNs in Compact Groups (CGs) as found by Martínez et al. (2008a) and corroborated in this study for HCGs, is consistent with very few gas left in these galaxies. In general, therefore, what may characterize the level of activity in CGs is a severe deficiency of gas.