For the members of the compact group of galaxies Shahbazian 4 the radial velocities are defined. The velocity dispersion is 440 km s−1. Moreover the appparent and absolute magnitudes of galaxies in the V band as well as the mass-to-luminosity ratio are obtained. The latter is approximately 220 M⊙/L⊙. The “crossing time” for the group Shahbazian 4 is equal to 4.7 × 107 years. It is one of the densest group of galaxies with n ~ 104 galaxies Mpc−3.

We searched for isolated galaxies, pairs and groups of galaxies in the CfA survey (Huchra et al. 1983). It was assumed that the distances to galaxies are given by R = V/H0, where H0 = 100 km s−1 Mpc−1 and R> 6 Mpc.

There are many studies on the correlation functions of galaxies, of clusters of galaxies, even of superclusters (e.g. Groth and Peebles 1977; Davies and Peebles 1983; Kalinkov and Kuneva 1985, 1986; Bahcall 1988 and references therein) but not so many on pairs and groups of galaxies.

Galaxies, like plants, show a large variety of grafts: an individual of some type connects physically with a neighborhood of same or different type. The effects of these interactions between galaxies have a broad range of morphologies depending, among other quantities, on the distance of the closest approach between systems and the relative size of the two galaxies. A sketch of the possible situations is shown in Table 1. This ‘botanical’ classification is just indicative, because the effects of interactions can be notable also at relatively large separations, when additional conditions are met: as for example low density of the interacting systems or the presence of intra-cluster gas. In spite of the large variety of encounters and effects, in the literature the same terms are often used to refer to different types of interactions.

The extensively studied Markarian sample of 1500 ultraviolet excess galaxies contains many Seyfert, starburst, and peculiar galaxies. Using the 20 minute V plates obtained for the construction of the Hubble Space Telescope Guide Star Catalog, we have investigated the morphologies of the Markarian galaxies and the environments in which they are located. This paper reports on the relationship between the types of nuclear activity and the morphologies and environments of the Markarian galaxies.

NGC 7592 = VV 731 = MCG-01-59-017 is a system of close interacting galaxies. Two main galactic bodies are present in the CCD R-band image taken at the 1.8m, F/9 telescope of the Asiago Observatory and shown in Figure 1:

• a north-western (NW) component (≡VV 731B), whose starlike nucleus (A) shows a Seyfert-type spectrum (Archipova et al., 1981). A is surrounded by a nearly spheroidal envelope, with an extension in the west at P.A. = 290° detected up to a distance from A of ≈ 9 arcsec, which corresponds to ≈ 2.5h-1kpc of projected linear distance (1 arcsec ≈ .35 h-1kpc at the redshift z = 0.0244; H0 = 100 h km s-1Mpc-1). This extension seems to bend in the northern direction and to join a bright wing, detected up to « 22 arcsec from A, which turns to east and resembles a spiral arm or a tidal tail.

• The envelope around A is connected (over ~ 20 arcsec 7h-1kpc) to a second galactic body (SE) located in the south-east of it. Its nucleus (B), identified by Markarian and Lipovetskii (1976) as the nucleus of Mkn 928, is located at dAB ~ 11 arcsec(~ 4h-1kpc) from A at P.A. = 100°. The morphology of this component is highly peculiar. In the central region, B is linked to two fainter knots which extend up to d″ ~ 4 arcsec at P.A. — 90°. This structure gives to the region surrounding B an elongated and distorted shape. Moreover, a bar-like structure is detected on either sides of B. The north-eastern side of the bar (P.A. = 40°) joins a slightly distorted loop of condensations, which can be traced from P.A. = 335° (at a distance from B«6 arcsec % 2.1 h-1kpc) to P.A. = 100° and from P.A. = 200° to P.A. = 240°, but not in corrispondence of the contact region between the two galaxies. This structure seems to be drained and distorted in the direction of a third condensation C at dBC ≈ 11.7 arcsec (≈ 4.1 h-1kpc) from B at P.A. — 212°. A faint plume bent in a direction opposite to that expected for spiral arms of the SE galaxy appears to extend from the west side of C.

It seems obvious that the evolution of star formation rate and hence of gas content in galaxies strongly depends on their environment. It reveals itself in particular in enhanced star formation or even in a strong burst of activity of massive stars often observed in an interacting galaxies. Nevertheless it should be noted that the time scale for the gas to be exhausted in these galaxies is unknown even approximately. To clarify a role of surroundings in the evolution of disk galaxies we should compare the HI content of isolated and non-isolated galaxies otherwise similar by their properties.

The dwarf irregular galaxy GR8, which is at the extreme faint end of the luminosity and mass functions, is studied using optical photometry and 21cm HI line observations. It is shown that rotation is only important to the gravitational support of the system in the inner parts (r < 250 pc). GR8 is one of the very few non-elliptical systems known (with M81dwA) where the random motions provide essentially all the support in the outer parts (r ≥ 500 pc). The Gaussian nature of the HI distribution and the isothermal distribution of the HI velocity dispersion implies M α R3 in the outer regions of GR8 (ie the stellar disk and the HI lie in the approximately uniform density core of the dark halo).

The southern S0+ galaxy NGC 7020 presents an unusual morphology: it includes a very regular outer ring which is completely detached and which envelops an inner ring/lens zone with a hexagon surrounding an X shape (Figures 1a and 1b). The outer ring has a high contrast compared to those usually observed in barred galaxies, yet NGC 7020 is not obviously barred. The morphology of this galaxy poses an interesting puzzle in that the hexagonal/X zone is not a typical type of feature to find in the interior of such a regular ring. Instead, the zone bears a striking resemblance to the edge-on galaxy IC 4767, recently studied by Whitmore and Bell (1988 = WB88) and dubbed by them as the “X-galaxy” because its inner regions appear to be crossed by two distinct enhancements lined at ±22° with respect to the major axis. The observation of a similar phenomenon in NGC 7020 is interesting because of the suggestion by WB88 that “X” structures could be related to accretion of matter associated with a merger or tidal encounter between an SO and a small satellite galaxy. If this interpretation is correct for NGC 7020, then it has important implications for the nature of the outer ring. An alternative interpretation is that the inner hexagonal/X zone is a region where resonant periodic orbits in a weak bi-symmetric potential perturbation are influencing the morphology more strongly than might be expected. In this paper, I give a brief summary of a more extensive paper (Buta 1990c = B90c) and a few other details concerning this interesting galaxy.

Over the last 20 years, a number of workers have studied the multiple nuclei cD galaxy in the rich Abell cluster 1775, trying to discover its nature. In all the cases though, very little has been published concerning its morphology. The majority of arguments about the nature of the this object have been based on the relative radial velocities of the 2 components with each other and with the other galaxies in the cluster, or its radio morphology. Very little work has been done on the optical morphology. To rectify that lack of data, we have obtained BVRI CCD images of the cD. We find from our CCD data that the cD is unlikely to be a bound object and that there is strong evidence for an collision.

On the basis of direct UBV and spectral observations at Tautenburg (DDR) 2m and Special Observatory (USSR) 6m telescopes respectively the colorimetric and spectral investigations of the megamaser galaxy MRK 273 are carried out. It is seen that: MRK 273 is in a physical group of galaxies, which contains at least five members. Two bright central condensations of MRK 273 are Seyfert nuclei. The area of the main body of MRK 273 which contains both Seyfert nuclei and from which comes out a straight tail, is redder than the remaining part of the galaxy. The tail has a pronounced blue color and most probably radiates in [OIII] λ5007 line. Observed radio continuum, OH and HI absorption features are related to bright “a” nucleus of galaxy. We come to the conclusion that MRK 273 which is the member of the group of the galaxies is itself a close system of two objects with AGNs. The tail, with radiation being of thermal origin, probably is the result of the interaction of these galaxies.

We present observations of HI emission from the peculiar galaxy NGC 660. HI was detected in the companion galaxy UGC 01195 as well. Sixteen hours of observations were obtained with the VLA telescope of the National Radio Astronomy Observatory during December 1986 and March 1987.

We report the discovery of a large (15 kpc diameter) Hα+[NII] emission-line disk in the elliptical galaxy IC 1459, showing weak spiral structure. The line flux peaks strongly at the nucleus and is more concentrated than the stellar continuum. The major axis of the disk of ionized gas coincides with that of the stellar body of the galaxy. The mass of the ionized gas is estimated to be ~ 1 105 M⊙, less than 1% of the total mass of gas present in IC 1459. The total gas mass of 4 107 M⊙ has been estimated from the dust mass derived from a broad-band colour index image and the IRAS data. We speculate that the presence of dust and gas in IC 1459 is a signature of a merger event.

Disturbed Galaxies with two nuclei display the final state of the interaction process of two galaxies (Kollatschny et al., 1986; Fricke and Kollatschny, 1989). A few of these double nucleus galaxies contain Seyfert nuclei.

Long slit spectroscopy and imaging of Mkn 423 and Mkn 739 have been performed at the 2.2 m and 3.5 m telescopes of the Calar Alto Observatory using both CCD and photographic detectors. Low and medium resolution spectra (1.8Å, 3.5Å, 6.0Å) together with V images have permitted to demonstrate the merging nature of Mkn 423 and the double structure of the NLR of its Seyfert component. This last feature has been found also in the NLR of the Seyfert component of Mkn 739, a double system the two components of which are counterrotating.

Polar-ring galaxies (PRG) are among the most interesting examples of interaction between galaxies. A PRG is a galaxy with an elongated main body surrounded by a ring (or a disk) of stars, gas, and dust rotating in a near-polar plane (Schweizer, Whitmore, and Rubin, 1983). Accretion of matter by a massive lenticular galaxy from either intergalactic medium or a companion galaxy is usually considered as an explanation of the observed structure of PRG. In the latter case there are two possibilities: (1) capture and merging of a neighbor galaxy, and (2) accretion of mass from a companion galaxy during a close encounter. Two PRG formation scenarios just mentioned are illustrated here by the results of our observations of the peculiar galaxies NGC 2685 and NGC 3808B.

In this paper we present the preliminary results of our radio-continuum and neutral hydrogen observations of Sérsic-Pastoriza (S-P) galaxies. We show that the central regions contain a population of compact features thought to be young supernova remnants (SNRs) and discuss the overall morphology of the nuclei.

The interaction of galaxies not only occurs in galactic scales, but also may be linked to the binary cores in active galactic galaxies. The presence of a binary in the center of galaxies was suggested by Begelman, Blandford and Rees (1980). Gaskell (1983) suggests that supermassive binaries may account for the observed structure of emission line profiles such as double peaks displaced by a significant velocity difference. Collin-Souffrin, et al. (1986) argue that line emission may be formed in the outer part of an accretion disk. The resultant profile, as expected from rotational motion, would be very broad and often possess a double-horn shape. However, the emission line profiles in most active galactic nuclei do not share such a resemblance, and there are only two reported cases, 3C390.3 (Pérez et al. 1987) and Arp102B (Chen, Halpern and Filippenko 1989), in which the broad Balmer line profile may be of such a shape. Therefore, the assumption for accretion disk is to be verified with care.

For a sample of 122 rich Abell clusters we find a strong correlation of the position angle (orientation) of the first-ranked galaxy and its parent cluster. This alignment effect is strongest for cD-galaxies. Formation scenarios for cD galaxies, like the merging scenario, must produce such a strong alignment effect. We show some N-body simulations done for this purpose.