Shakhbazian Compact Galaxy Groups Research Articles

Photometric observations of nine Shakhbazian compact groups

By observations with the 1.5m telescope at San Pedro Martir (OAN, UNAM, Mexico) the BVR magnitudes are determined for 66 member galaxies in Shakhbazian Compact Galaxy Groups ShCG 40, ShCG 176, ShCG 270, ShCG 278, ShCG 310, and ShCG 342. Three other groups were observed in two or only in one band. Seven galaxies in ShCG 298 were observed in B and R, six galaxies in ShCG 95 were observed in V, and seven galaxies in ShCG 345 were observed in V and R. The distribution of brightness of observed galaxies is determined. Signs of interaction between galaxies are detected in some groups.

Redshifts of 19 Shakhbazian compact groups of galaxies

By observations at Calar Alto (Spain), La Silla (Chile) and Cananea (Mexico), we measured redshifts of 108 candidate members in 19 Shakhbazian compact galaxy groups ShCG 44, 105, 149, 168, 270, 276, 278, 279, 298, 303, 304, 310, 317, 331, 339, 340, 345, 358, and 359. Redshifts of another ten members were taken from the NED. We found that nine out of 118 candidate member galaxies are stars, and twelve galaxies are not members of the corresponding groups and are projected over them. The group ShCG 168 is the core of a cluster. The groups ShCG 276, ShCG 298, and ShCG 303 are either strongly contaminated by field galaxies with redshift differing not very much from that of the corresponding group, or are the results of a chance projection of field galaxies.

Photometric and spectroscopic study of the Shakhbazian compact galaxy groups ShCG 254, ShCG 257, ShCG 351, and ShCG 371

Results of a detailed spectroscopic and photometric study of the four Shakhbazian compact galaxy groups ShCG 254, ShCG 257, ShCG 351, and ShCG 371 are reported. The redishifts of the member galaxies and radial velocity dispersions in these groups have been determined. The R surface brightness distributions of the member galaxies have been studied. The morphological types of the galaxies have been determined based on the profiles of the surface brightness, µ, as functions of the semimajor axis α1/4 or α. Some members of the groups are in the process of interacting. Curves of isophotal twisting and the Fourier parameter α4 have been plotted. The physical parameters of the groups (radial velocity dispersions, virial radii and masses, luminosities, mass-to-luminosity ratios, and crossing times) have also been derived.

Shakhbazian compact galaxy groups

Shakhbazian compact galaxy groups belong to the interesting class of compact groups. Because of their large number (the catalogue contains 377 entries) we are able to study the groups in dierent stages of evolution. Here we give the results of detailed study of four groups, ShCG 154, ShCG 166, ShCG 328 and ShCG 360. We present the redshifts of individual galaxies in groups, the results of the surface photometry in BVR, the contourplots of the surface brightness versus eective radius of galaxies, the twisting postion angle versus eective radius of galaxies, the radial velocity dispersions, the crossing times, the mass-to-luminosity ratios of groups and the results of the X-ray study. The dynamical state of groups, interactions between member galaxies, and the physical parameters of groups are discussed.

AGNs in Shakhbazian Compact Groups

The results of CCD spectroscopic observations of Shakhbazian compact groups of galaxies (SHCGs) with the 1.54-m (La Silla, Chile), 2.2-m (Calar Alto, Spain) and 2.6-m (Byurakan) telescopes are presented. According to these preliminary data, about 10% of member galaxies in SHCGs are emission-line galaxies (ELGs) including the broad-line AGNs (of classical Seyfert 1 type) and the narrow-emission-line galaxies.A research program has been developed in the University of Potsdam, Potsdam Astrophysikalisches Institut in cooperation with other observatories (particularly with Byurakan Astrophysical Observatory) to perform photometric and spectroscopic investigations of galaxies in the SHCGs. Within the framework of this program the redshift (radial velocity) measurements have been carried out for more than 200 galaxies in 36 SHCGs. The MIDAS software package was used for processing and interpreting of the galaxy spectra. Most of these redshifts were measured for the first time. 180 member galaxies (90%) in these groups have absorption spectra typical of E and SO galaxies. Twenty galaxies (10%) turn out to be ELGs. They are in the range 0.02 ≤ z ≤ 0.17, i.e., the SHCGs lie in approximately the same redshift space as Abell clusters. These compact groups contain predominantly elliptical and lenticular galaxies (del Olmo 1988; Amirkhanian 1989) like the cores of rich, regular, centrally condensed clusters of galaxies. The fraction of spirals falls in the densest matter concentrations. On the other hand, it is a well-established fact that in the local universe the active objects tend to avoid the cores of dense clusters of galaxies (e.g. Green and Yee 1984). That is why the discovery of an emission-line population with broad-line AGNs in SHCGs (Tiersch et al. 1999) was unexpected. As shown by Dressier, Thompson and Shectman (1985) in their sample of 1268 galaxies in the feilds of 14 rich clusters the ELGs comprise 31% of the field galaxies but only 7% of the cluster galaxies. Similarly, according to their statistics AGNs make up 5% of the field sample, but only 1% of the cluster sample. They note that the difference in the distribution of morphological types can only partially explain this effect. Obviously, some sort of environmental influence is present.

Far-infrared emission from Shakhbazian Compact Galaxy Groups

Using the IRAS archives, we searched for far-infrared (FIR) counterparts of Shakh bazian Compact Groups of Galaxies (SCGGs). Reliable IRAS detections are identified at the positions of 24 out of 367 SCGGs; another 10 IRAS sources, located within ~2 arcmin of SCGGs, are possibly associated with the corresponding galaxy groups. Some of these sources are not very reliable. Previous work has shown that the fraction of E and S0 galaxies in a representative sample of SCGGs is 77%, while E and S0 galaxies comprise about 51% of galaxies in Hickson Compact Groups (HCGs). The higher fraction of early Hubble types, combined with their greater distances, explains the low IRAS detection rate of SCGGs (7-8%) compared to HCGs (64%). The FIR colors and morphological types of galaxies in the groups suggest that active star formation or Seyfert galaxies may be the main source of the FIR emission in the SCGGs detected by IRAS, perhaps originating as the result of tidal interactions in the dense environments of these groups.

The shapes of Shakhbazian compact groups of galaxies

AbstractWe have completed an investigation (preliminary results for which were reported in Oleak et al. 1995) into the shapes of Shakhbazian compact groups of galaxies. Ellipticites for 299 groups in the Shakhbazian survey have been examined using the technique proposed by Rood (1979) for deriving the average “flatness” of a large sample of objects. The distribution of the apparent axial ratios (g = b/a) for the groups is found to be broad with a mean of< b/a > ∽ 0.5. This distribution is compared with randomly generated spherical and elliptical model systems. The results confirm the findings of our earlier study: the frequency distribution of axial ratios for Shakhbazian groups is represented soley by a population of prolate spheroids with low intrinsic axial ratios, < q > = 0.3, σ = ∽0.17 (assuming random true orientations in 3D space). This now provides further strong evidence that the Shakhbazian groups are more highly flattened than either rich clusters or elliptical galaxies, and represent the most elongated systems yet found. The result also provides confirmation of the reality of the groups, since in the case of systems of chance line‐of‐sight superpositions of galaxies we would expect to see much higher axial ratios.

On the completeness of the lists of Compact Galaxy Groups

AbstractIt is shown that the lists of Shakhbazian Compact Galaxy Groups (SCGGs) are not complete. The number of the detected groups in the strip between b = ±30° and b = ±20° is by four to five times smaller than expected. The most probable reason is that during the search for SCGGs it was hard to distinguish images of compact galaxies from that of stars on the POSS prints in dense areas of the sky at lower galactic latitudes. There is some deficit of the detected groups between 60° and 40° of the north galactic latitudes. The surface density of SCGGs in the southern galactic hemisphere between b = −50° and b = −30° is by about three times less than it is expected. Obviously, the southern sky has not been searched properly. The list of Hickson's groups is complete down to galactic latitude ±30°. However, some excess of HCGs is found in the southern hemisphere, where the surface density of the found groups is by about two times higher than that of in the northern hemisphere.

Catalogue of Shakhbazian compact groups of galaxies. X

AbstractThe tenth part of the catalogue of Shakhbazian groups contains the positions and references of all the galaxies of the following 35 groups (north of δ > +2°30'): Shkh 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 354, 355, 356, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377. For the estimation of the coordinates the Digitized Sky Survey was used.

On the ellipticity of the Shakhbazian compact groups of galaxies

On the ellipticity of the Shakhbazian compact groups of galaxies

Photometric catalogue of Shakhbazian compact groups of galaxies. III.

AbstractThe third part of the photometric catalogue of Shakhbazian compact groups of galaxies contains optical and geometrical properties of another 24 groups (Shkh 288, 289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 300, 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312). As in the first paper photometric data were obtained from the COSMOS/UKST catalogue of the Southern sky with δ ⩽ +2°30'. The survey of compact galaxy groups by Shakhbazian, Petrosian, Baier, and Tiersch is a basis for studying physical properties of such groups.

Photometric catalogue of Shakhbazian compact groups of galaxies. IV.

AbstractThe fourth part of the photometric catalogue of Shakhbazian compact groups of galaxies contains optical and geometrical properties of another 26 groups (Shkh 313, 314, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 357). As in the previous papers photometric data were obtained from the COSMOS/UKST catalogue of the Southern sky with δ ± +2°30'. The survey of compact galaxy groups by Shakhbazian, Petrosian, Baier, and Tiersch is a basis for studying physical properties of such groups.

Photometric catalogue of Shakhbazian compact groups of galaxies. II

AbstractThe second part of the photometric catalogue of Shakhbazian compact groups of galaxies contains optical and geometrical properties of another 24 groups (Shkh 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276, 277, 278, 279, 280, 281, 282, 283, 284, 285, 286, 287). As in the first paper photometric data were obtained from the COSMOS/UKST catalogue of the Southern sky with δ ≤ +2°30′. The survey of compact galaxy groups by Shakhbazian, Petrosian, Baier, and Tiersch is a basis for studying dynamical processes in such groups.

Photometric catalogue of Shakhbazian compact groups of galaxies. I

AbstractCompact groups of galaxies are fruitful laboratories to study such processes as dynamical friction, tidal interaction, collision, and galaxy mergers. The largest survey of compact galaxy groups is the one of Shakhbazian, Petrosian, Baier, Tiersch. A programme to evaluate photometrical properties of the galaxies in the Shakhbazian groups has been started using the COSMOS/UKST catalogue of the Southern sky with δ ≤ + 2°30′. About a quarter of the Shakhbazian groups lie south of this declination limit. A list of 24 groups (Shkh 21, 24, 27, 30, 32, 33, 35, 81, 82, 83, 140, 141, 143, 144, 145, 146, 147, 148, 151, 152, 154, 261, 262, 263) is our first result.