Emission-Line Galaxies in Shahbazian Compact Groups

Abstract

Based on the CCD photometric and spectroscopic observations taken with 1.23 m and 2.2 m telescopes at the German-Spanish Astronomical Center in Calar-Alto (Almeria, Spain) as well as with the 1.54 m telescope at the European Southern Observatory (La Silla, Chile) some emission-line galaxies (ELGs) surprisingly have been found in Shahbazian compact groups of galaxies (SHCGs) by our research group. . The majority of galaxies in the SHCGs usually have an absorption spectra typical of ellipticals and SOs. But some of these objects turn out to be the ELGs including two broad-line AGNs (of classical Seyfert 1 type) and the narrow emission-line galaxies. Their redshift makes these galaxies a physical member of the host group.Unlike well studied Hickson compact groups (HCGs) (see e.g. Hickson 1993; Hickson "1997) not many SHCGs of galaxies have been investigated photometrically and spectroscopically till quite recently (Tiersch et al. 1998 and references therein). For this reason a program has been started in the University of Potsdam, Potsdam Astrophysikalisches Institut in cooperation with other observatories to obtain photometric and spectroscopic properties of the galaxies in SHCGs (Tiersch et al. 1994;Oleak et al. 1995;Tiersch et al. 1995).The main goal of our program is to study the physical nature of these groups, their past and future evolutionary histories. With this purpose it is necessary to know the morphology of member galaxies, the photometric data, i. e. B, V, R apparent magnitudes, radial velocities, velocity dispersion, mass-to-Iuminosity ratio, crossing times, dynamics, chemical abundance, metallicity as well as the evolution effects.Three-colour (B, V, R) photometric and spectroscopic observations have been carried out at Calar Alto and La Silla Observatories by Tiersch and Stoll. The data reduction procedure used the MIDAS software package at Potsdam Astrophysikalisches Institut.

AGNs in Shakhbazian Compact Groups

“…Finally we note that Shk 355/4 is a classical Seyfert 1 galaxy at the same redshift as its host group with z=0.0943 (Tiersch et al 1999). Moreover Shk 278/4 is also a broad-line AGN in an early-type galaxy (z=0.1205).…”

“…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.…”

AGN populations in compact groups of galaxies

“…According to our preliminary data about 7-10% of member galaxies in Shahbazian compact groups are the emission line galaxies including the broad-line AGNs (of classical Seyfert 1 type) and the narrow emission-line galaxies (Tiersch et al (1999), Amirkhanian et al (2010). Their redshift makes these galaxies a physical member of the hosted group.…”