Compact groups in the UZC galaxy sample^*

II. Connections between morphology, luminosity and large-scale density

Dipartimento di Astronomia, Università di Bologna, Via Ranzani 1, 40127 Bologna, Italy

Corresponding author: B. Kelm, birgit.kelm@unibo.it

Received: 26 December 2002
Accepted: 12 February 2004

Abstract

The nature of Compact Groups (CGs) is investigated by comparing the luminosities and morphologies of CG galaxies, CG Neighbours and Isolated galaxies. CGs turn out to include more early type galaxies than Isolated galaxies and fewer low-luminosity galaxies. The 33 CGs with a dominant E/S0 and the 30 CGs with a dominant spiral have similar LF parameters. Spiral dominated CGs have fewer galaxies at high and low luminosity in comparison with their Neighbours, while E-S0 dominated CGs seem to lack only faint galaxies when compared to their Neighbours. Ellipticals which are the dominant galaxy of a CG are also brighter than all their Neighbours, while this holds true for only half of the dominant spirals and S0s. Relations linking the number of Neighbours of dominant E-S0s to the luminosity of E-S0s and to the difference between the first and the second ranked CG members do suggest a link between the formation of bright early-type galaxies and the presence of a group-like potential. No similar relations are found for dominant spirals. These tentative results are compatible with the assumption that CG dominant Ellipticals are anomalous galaxies whose formation might have been a secondary outcome during the process of groups formation.