Comparing galaxy populations in compact and loose groups of galaxies

Instituto de Astronomía Teórica y Experimental (IATE), CONICET-Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, X5000BGR Córdoba Argentina
e-mail: vcoenda@oac.uncor.edu; hernan@oac.uncor.edu; julian@oac.uncor.edu

Received: 21 October 2011
Accepted: 15 May 2012

Abstract

Aims. We compare the properties of galaxies in compact groups, loose groups, and the field to deepen our understanding of the physical mechanisms acting upon galaxy evolution in different environments.

Methods. We select samples of galaxies in compact groups, loose groups, and field galaxies from the Sloan Digital Sky Survey. We compare the properties of the galaxy populations in these different environments: absolute magnitude, colour, size, surface brightness, stellar mass, and concentration. We also study the fraction of red and early-type galaxies, the luminosity function, the colour-luminosity, and luminosity-size relations.

Results. The population of galaxies in compact groups differ from that of loose groups and the field. The fraction of red and early-type galaxies is larger in compact groups. Galaxies in compact groups are, on average, systematically smaller in size, more concentrated, and have higher surface brightnesses than galaxies in the field and in loose groups. At a fixed absolute magnitude, or fixed surface brightness, galaxies in compact groups are smaller in size.

Conclusions. The physical mechanisms that transform galaxies into earlier types could be more effective within compact groups, owing to the typically high densities and small velocity dispersions of these environments, which could explain the large fraction of red and early-type galaxies we found in compact groups. Galaxies inhabiting compact groups have undergone a major transformation compared to galaxies that inhabit loose groups.