AGNs in Shakhbazian Compact Groups

The results of CCD spectroscopic observations of Shakhbazian compact groups of galaxies (SHCGs) with the 1.54-m (La Silla, Chile), 2.2-m (Calar Alto, Spain) and 2.6-m (Byurakan) telescopes are presented. According to these preliminary data, about 10% of member galaxies in SHCGs are emission-line galaxies (ELGs) including the broad-line AGNs (of classical Seyfert 1 type) and the narrow-emission-line galaxies.A research program has been developed in the University of Potsdam, Potsdam Astrophysikalisches Institut in cooperation with other observatories (particularly with Byurakan Astrophysical Observatory) to perform photometric and spectroscopic investigations of galaxies in the SHCGs. Within the framework of this program the redshift (radial velocity) measurements have been carried out for more than 200 galaxies in 36 SHCGs. The MIDAS software package was used for processing and interpreting of the galaxy spectra. Most of these redshifts were measured for the first time. 180 member galaxies (90%) in these groups have absorption spectra typical of E and SO galaxies. Twenty galaxies (10%) turn out to be ELGs. They are in the range 0.02 ≤ z ≤ 0.17, i.e., the SHCGs lie in approximately the same redshift space as Abell clusters. These compact groups contain predominantly elliptical and lenticular galaxies (del Olmo 1988; Amirkhanian 1989) like the cores of rich, regular, centrally condensed clusters of galaxies. The fraction of spirals falls in the densest matter concentrations. On the other hand, it is a well-established fact that in the local universe the active objects tend to avoid the cores of dense clusters of galaxies (e.g. Green and Yee 1984). That is why the discovery of an emission-line population with broad-line AGNs in SHCGs (Tiersch et al. 1999) was unexpected. As shown by Dressier, Thompson and Shectman (1985) in their sample of 1268 galaxies in the feilds of 14 rich clusters the ELGs comprise 31% of the field galaxies but only 7% of the cluster galaxies. Similarly, according to their statistics AGNs make up 5% of the field sample, but only 1% of the cluster sample. They note that the difference in the distribution of morphological types can only partially explain this effect. Obviously, some sort of environmental influence is present.