This report presents basic observational parameters for galaxy triplets selected by criterion of their isolation on the sky (=Catalog of Triple Galaxies, Karachentseva et al, 1979). The CTG sample is compared with a sample of wide triple systems from Nearby Galaxies Catalog (Tully, 1988) as well from a new whole-sky catalog of small galaxy groups in the Local Supercluster (Makarov & Karachentsev, 2000). For all the samples their medians of the virial mass-to-luminosity ratio lie in a narrow range, 31 < Mvir/L < 36 (M⊙/L⊙), while the medians of the crossing time occupy a wider range, 0.07 < Tcross < 0.37 (in 1/H units).

Using the ESO/SERC and POSS-I sky surveys we selected 76 isolated triple systems of galaxies with Dec. < −3°. For each triplet the equatorial coordinates, type of configuration, angular diameters, apparent angular separation of the components, morphological types, total magnitudes and some other characteristics are presented. 33 of 76 triplets have the measured radial velocities for all the components. The median values of basic dynamic parameters: a radial velocity dispersion, mean harmonic separation, an absolute magnitude of galaxies, mass-toluminosity ratio are very close to those obtained earlier for 83 northern isolated triple systems from the list of Karachentseva et al. (1979).

Compact groups of galaxies are an extreme class of object, ideal for the study of galaxy interactions and their effects. In this paper we present a new algorithm, devised to select compact groups from digitized catalogues of galaxies and especially suited to reach fainter magnitudes. We present also the results obtained from the redshift survey of the bright subsample of such groups.

We have identified close pairs and triplets of galaxies in SDSS commissioning imaging data. The data set is from one of the SDSS equatorial scans covering an area close to 100 square degrees. We have estimated the angular correlation function of these galaxy systems and show that they appear to be appreciably more strongly clustered than are single galaxies.

Some problems and statistical approaches in studies of galaxy groups are discussed.

A new approach is suggested which makes use of the individual properties of galaxies, for the identification of small galaxy groups in the Local Supercluster. The criterion is based on the assumption of closed orbits of the companions around the dominating group member within a zero velocity sphere.

The criterion is applied to a sample of 6321 nearby galaxies with radial velocities V0 ≤ 3000 km s−1. These 3472 galaxies have been assigned to 839 groups that include 55% of the sample considered. For the groups identified by the new algorithm (with k ≥ 5 members) the median velocity dispersion is 86 km s−1, the median harmonic radius is 247 kpc, the median crossing time is 0.08(1/H), and the median virial-mass-to-light ratio is 56 M⊙/L⊙.

The kinematics of galaxies belonging to the Hickson compact group HCG67 are investigated. The latter consists of four galaxies, three of which (a, c, d) are embedded in a common envelope. The fourth galaxy (b) is a spiral that is detected both in radio and in IR wave-bands. Our observations show that the three galaxies in apparent interaction are probably caught during an ongoing merger process.

We present measurements of stellar kinematics for seven early-type galaxies in HCG 67, HCG 74 and HCG 79. These data are aimed at studying the relation between the environment and the dynamics, structure and stellar content of early-type galaxies. In the present three groups, the kinematic features we observed cannot be associated unambiguously to physical interactions. Visible morphological peculiarities do not appear correlated with kinematical perturbations.

An analysis of the kinematics of the five major spiral galaxies in the Sculptor Group is presented. These galaxies are analyzed using the method of harmonic expansion of the velocity field as described in Schoenmakers, Franx and de Zeeuw (1997). Three different types of kinematic distortions were found: warps, lopsidedness and elongation. All the Sculptor galaxies show kinematic lopsidedness, two show signs of global elongation and two are kinematically warped. The detected kinematic distortions are well in excess of those typically found for isolated galaxies.

We describe a long-term program based on Fabry-Perot Hα velocity field data of compact groups taken at the ESO and the CFH 3.6m telescopes. The main goals of our project are: 1) determine the evolutionary stages of the studied groups, 2) search for tidal dwarf galaxy candidates in interacting systems and 3) in combination with photometry available in the literature, determine the Tully-Fisher relation for the group galaxies. In this paper we summarize all the Hα Fabry-Perot data we have obtained to date and present a preliminary discussion of point 1).

The sample of 18 systems (with 64 galaxies) studied here contain groups at a variety of dynamical stages: from a false group that is in fact one single irregular galaxy with several star-forming blobs (e.g. HCG 18) to a group whose members are strongly interacting and possibly forming tidal dwarf galaxies (e.g. HCG 92) to a group in the final process of merging (e.g. HCG 31). A companion paper (Amram and Mendes de Oliveira, 2000) shows examples of galaxy velocity fields for groups in different dynamical stages.

Two-color CCD photometry of dwarf galaxies in and around the M81, M101 and CVnI groups is presented. These observations are part of a long term project aimed at obtaining surface photometry data of all known dwarf galaxies within 10 Mpc. The global photometric parameters derived will serve as the basis for a comparison between dwarf galaxies in different galactic environments.

The properties of dust in giant elliptical galaxies are reviewed, with particular emphasis on the influence of the environment.

After normalizing by the optical luminosities, a strong anticorrelation between the masses of dust and hot gas in X-ray bright ellipticals is found. Furthermore, large-scale, regularly-shaped dust lanes (which are symmetric with respect to the galaxy nucleus) are only found to be present in ellipticals with the lowest ratios of the mass of hot gas to the blue luminosity (Mhot/LB ≲ 0.04 in solar units). This can be explained by the short time scale for the destruction of dust grains within the hot, X-ray- emitting gas compared to the formation timescale of such dust lanes in early-type galaxies.

Dust within ellipticals in “loose” environments (i.e. in the field or in loose groups) is typically characterized by small values of RV ≡ AV/EB−V (i-e. small characteristic grain sizes), and distributed in dust lanes with a smooth, relaxed morphology. On the other hand, dust in ellipticals that are in or near the center of dense groups or clusters is typically much more irregularly distributed, and characterized by RV values that are close to the Galactic one.

I predict that ellipticals containing “relaxed” dust lanes with typical dust masses of 106 − 107M⊙ do not contain hot, X-ray-emitting gas.

From R-band images of 39 Hickson compact groups (HCGs), we use galaxy counts to determine a luminosity function. We find that a single Schechter function is a poor fit to the data, so we use a composite function consisting of separate Schechter functions for the bright and faint galaxies. The decreasing bright end slope implies a deficit of intermediate luminosity galaxies in our sample and the faint end is slightly steeper than that reported for earlier HCG luminosity functions. Furthermore, luminosity functions of subsets of our sample reveal more substantial dwarf populations for groups with X-ray halos, groups with tidal dwarf candidates, and groups with a dominant elliptical or lenticular galaxy. Collectively, these results support the hypothesis that within compact groups, the initial dwarf galaxy population is replenished by “subsequent generations” formed in the tidal debris of giant galaxy interactions.

The mean absolute luminosities and diameters of galaxies in double and triple configurations are compared with the same characteristics for single galaxies. Members of optical pairs and triplets are used as the sample of single galaxies. The mean luminosities of galaxies in physical pairs and triplets are found to be the same as for single galaxies. At the same absolute luminosity, single galaxies have larger diameters compared to galaxies in pairs and triplets.

A method of searching for multiplets in a large catalogue of galaxies with measured redshifts is described. Compact Groups samples having different local and global characteristics are generated when the algorithm is applied to ZCAT catalogue. Both local and environmental galaxy density have been computed thus allowing to define truly isolated compact groups as well as compact groups in dense and medium dense environments. We find 40% of our compact groups to be isolated while as much as 20% are identified in high density structures.

The compact group of galaxies “Seyfert’s Sextet” shows irregularly shaped soft X-ray morphology. In order to understand its origin, we have obtained a deep optical (VR + I) image of the group. Our image shows that a faint envelope surrounds the member galaxies. We find that optical and soft X-ray images are significantly similar in morphology. This similarity provides direct morphological evidence that the dark matter in Seyfert’s Sextet was originally associated with the individual galaxies and is now spreading out around the group.

We have found a new, very compact group of galaxies characterized by a median projected separation between galaxies of 5.2/h kpc and a very low velocity dispersion. All the observed member galaxies show emission line spectra and a disturbed morphology. From these properties it emerges that this compact group is in an extremely advanced stage of evolution.