Nature Of Compact Groups Research Articles

Compact groups in the UZC galaxy sample

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.

The Fundamental Plane of Elliptical Galaxies in Compact Groups

We present a study focusing on the nature of compact groups through the study of their elliptical galaxies. We determine velocity dispersions (σ) for 18 bright elliptical galaxies located in the core of Hickson compact groups and a control sample of 12 bright bona fide elliptical galaxies located in the field or very loose groups. Several tests are carried out to avoid sources of systematic effects in σ measurements. We use these velocity dispersions to compare the positions of 11 compact group galaxies in the fundamental plane with those of a large and homogeneous sample of elliptical galaxies. We find that little or no significant difference exists, as far as the fundamental plane is concerned, between elliptical galaxies in compact groups and their counterparts in other environments.

Compact Groups of Galaxies: Evolution of the Stellar Population

We present a study focusing on the nature of compact groups (CGs) through the study of their elliptical (E) galaxies. Parameters describing the internal dynamics and the stellar populations of the galaxies are compared with their counterparts in other environments. Our sample has24 bright E galaxies located in the core of Hickson CGs and 11 bright ‘bona fide’ Es, located in the field or very loose groups. Their spectra were obtained with the 2.1 m Telescope at KPNO and have a 4.1 A resolution over the wavelength range 3500–7000 A. We have found that, from the dynamical point of view, E galaxies in CGs are essentially similar to those in dense clusters. Moreover, the stellar populations of Es in CGs seem to be older and less metal rich than those in the field, behaviour which has also been observed by Rose et al. (1994).

The Nature of Compact Groups

AbstractWe show that compact groups (CGs) are real physical entities, that almost all HCGs are dynamically associated with generally elongated loose groups of galaxies, that HCGs are compact cores of loose groups, and that they are longer living formations.