AGNs in Shakhbazian Compact Groups

Abstract

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.

Shakhbazian compact galaxy groups

“…Hickson et al 1989aHickson et al , 1989bHickson et al , 1992Hickson 1993), Shakhbazian Compact galaxy Groups (ShCGs) have not been intensively investigated. The redshifts of only a few groups have been measured until recently (Robinson & Wampler 1973;Arp et al 1973;Mirzoyan et al 1975;Kirshner & Malamuth 1980;Amirkhanian 1987;Kodaira et al 1988Kodaira et al , 1990Kodaira & Sekiguchi 1991;Lynds et al 1990;del Olmo & Moles 1991;Tiersch et al 1995aTiersch et al , 1995bTiersch et al , 1995cTiersch et al , 1996aTiersch et al , 1999aTiersch et al , 1999b, the morphology of galaxies in a few groups was studied by Amirkhanian & Egikian (1987), Bettoni & Fasano (1995) and Tiersch et al (1995c).…”

Compact Groups of Galaxies

“…After removing galaxies whose velocities differ from the group median by more that 1000 km s −1 , Hickson et al (1992) found that t d ∼ 0.02H −1 0 and obtained a mean mass-to-light ratio of 50h (solar units) for the HCGs. Similar values were found for several Shakhbazian groups (Tikhonov 1986, Amirkhanian & Egikian 1987, Amirkhanian 1989, Lynds et al 1990, Amirkhanian et al 1991. Since the mass-to-light ratios of individual HCG galaxies is on the order of 7h (Rubin et al 1991), the galaxies appear to contain only ∼ 15% of the total mass.…”

Shakbazian Compact Groups: Mass‐to‐light ratios and mass distribution models: I. ShCG 362 and ShCG 166

“…Radial velocities were determined for objects # 1, 2, 3, 5 and 8 by Amirkhanian & Egikian (1987) and for objects #1 to #8 by Tiersch et al (2002, hereafter T02); the median radial velocity is 11 890 km s −1 . All galaxies in this group are E and S0 types.…”