The DPOSS II distant compact group survey: the EMMI-NTT spectroscopic sample

Abstract

This paper presents the results of the redshift survey of 138 candidate compact groups from the DPOSS II catalog (Iovino et al., 2003; de Carvalho et al. 2005), which extends the available redshift range of spectroscopically confirmed compact groups of galaxies to z~0.2. The aims of the survey are to confirm group membership via spectroscopic redshift information, to measure the characteristic parameters of the confirmed groups, namely mass, radius, luminosity, velocity dispersion and crossing time, and to compare them with those of nearby compact groups. Using available information from the literature, we also studied the surrounding group environment and searched for additional, previously unknown, group members, or larger scale structures to whom the group might be associated. Of the 138 observed groups, 96 had three or more concordant galaxies, i.e. a 70% success rate. Of these 96, 62 are isolated on the sky, while the other 34 are close on the sky to a larger scale structure. The remaining objects turned out to be couple of pairs or chance projection of galaxies on the sky. Group environment and the characteristics parameters (mass, crossing time, velocity dispersion) are evaluated and discussed.