Shakhbazian compact galaxy groups

Tovmassian, H. M.; Tiersch, H.; Chavushyan, V.; Tovmassian, G.

doi:10.1051/0004-6361:20030129

Cited by 26 publications

(57 citation statements)

References 23 publications

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“…Tovmassian et al 1999). The similarity of the axial ratio distribution and its mean value between the original HCGs and the sample of HCG + environment systems studied here and in the work of Tovmassian & Chavushyan (2000) suggests that the HCG + environment systems also have a prolate-like shape.…”

Section: Correlation Of Velocity Dispersion Number Of Group Memberssupporting

confidence: 58%

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Physical properties of Hickson compact groups and of the loose groups within which they are embedded

Tovmassian

Plionis

Torres‐Papaqui

2006

A&A

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Using new data and an enlarged group sample we verify some of our previously published results and present a number of new facts that suggest that compact groups could be casual concentrations in prolate-like looser groups, and thus the nature of compact and ordinary poor groups is probably the same. To this end we used the Sloan Digital Sky Survey (SDSS) redshift catalogue to look for galaxies with accordant redshifts in the nearby environment (up to ∼2 Mpc) of 15 Hickson compact groups (HCG). We also used known member redshifts of looser groups in the environment of 7 other HCGs. From this sample of 22 HCGs we find that: (a) HCG's tend to be aligned with the overall galaxy distribution in their ∼1 Mpc environment; (b) the well-established orientation effect by which the group velocity dispersion σ v correlates with group axial ratio q is present and particularly strong also in the HCG + environment systems; (c) the velocity dispersion σ v of the HCG + environment systems as well as of ordinary poor groups, depends only weakly on the group richness, i.e. on the mass; (d) the mean absolute K-band magnitude of E/S0 galaxies in HCGs is similar to the corresponding one in ordinary poor groups and is brighter than that of isolated E/S0's, indicating that they were formed by the merging of two galaxies of similar luminosity; (e) the fraction of E/S0 galaxies in these HCGs depends, albeit weakly, on the group's richness and on σ v ; (f) the fraction of AGNs is similar in the HCGs and their close environment, while the fraction of starburst galaxies is significantly higher in the HCGs; (g) the fraction of active galaxies (AGNs and starbursts) is anti-correlated with the velocity dispersion of the HCG + environment systems. The combination of all the above facts constitutes a picture in which compact groups are condensations within looser prolate-like, elongated systems, and they appear to be compact when their member galaxies, moving in radial orbits along the group elongation, happen to come close to each other (in which case dynamical interactions among these galaxies become even more probable) or when the group is oriented close to the line of sight, so that many of its members are projected over a small solid angle. The probability of either case is small, so the number of CGs should be much smaller than that of ordinary groups, as observed. Furthermore, the observed fractions of early-type and active galaxies, as well as their correlations with the group velocity dispersion suggests a picture by which nuclear activity and galaxy transformation by merging is instigated by effective gravitational interactions in the low-velocity dispersion groups, which then dynamically evolve via virialization processes to higher velocity dispersion groups, which thus have a higher fraction of early-type galaxies.

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Section: Correlation Of Velocity Dispersion Number Of Group Memberssupporting

confidence: 58%

“…Tovmassian et al (1999) show that the velocity dispersion of HCGs correlates with their projected shape: the lower the group's projected axial ratio, the smaller its velocity dispersion. They conclude that member galaxies move in radial orbits predominantly along the group's elongation.…”

Section: Introductionmentioning

confidence: 93%

Physical properties of Hickson compact groups and of the loose groups within which they are embedded

Tovmassian

Plionis

Torres‐Papaqui

2006

A&A

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“…They were selected as dense groups of mainly red galaxies, the images of many of which were often hard to distinguish from those of stars. Through follow-up spectral observations (Tiersch et al 2002, hereafter Paper I;Tovmassian et al 2003a, hereafter Paper II, 2003b, hereafter Paper III, 2004a, hereafter Paper IV, 2004b, hereafter Paper V) it was found that some objects in the area of groups which were assumed in original papers to be stars, are in reality galaxies. On the other hand, only a Figures 1 and 3-10 are only available in electronic form at http://www.edpsciences.org few assumed members of ShCGs turned out to be stars.…”

Section: Introductionmentioning

confidence: 99%

Shakhbazian compact galaxy groups

Tovmassian

Tiersch²,

Chavushyan

et al. 2005

A&A

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Abstract. We present the results of a detailed spectroscopic and photometric study of four Shakhbazian compact groups: ShCG 8, ShCG 14, ShCG 19, and ShCG 22. We determined the redshifts of member galaxies and radial velocity dispersions of groups. We also studied the distribution of the surface brightness of member galaxies in R and determined their morphological types. The profiles of the surface brightness versus semi-major axis, the curves of isophotal twisting, and Fourier parameter a 4 are constructed. We found that some members of groups are in the process of interaction. We determined physical parameters of groups: virial masses, luminosities, mass-to-luminosity ratios, and the crossing times. On the basis of the results obtained in this and our previous works, the general properties of 22 ShCGs are discussed.Key words. galaxies: clusters: general -galaxies: distances and redshifts -galaxies: interactions -galaxies: generalgalaxies: kinematics and dynamics -galaxies: photometry IntroductionIn 1995 we commenced a spectroscopic and detailed photometric study of Shakhbazian compact groups (ShCGs). The list of ShCGs contains 377 groups (Shakhbazian 1973;Petrosian 1974Petrosian , 1978Baier et al. 1974;Baier & Tiersch 1975, 1976a, 1976b, 1978, 1979. ShCGs were found by an eye inspection of the POSS prints. They were selected as dense groups of mainly red galaxies, the images of many of which were often hard to distinguish from those of stars. Through follow-up spectral observations (Tiersch et al. 2002, hereafter Paper I;Tovmassian et al. 2003a, hereafter Paper II, 2003b, hereafter Paper III, 2004a, hereafter Paper IV, 2004b, hereafter Paper V) it was found that some objects in the area of groups which were assumed in original papers to be stars, are in reality galaxies. On the other hand, only a Figures 1 and 3-10 are only available in electronic form at http://www.edpsciences.org few assumed members of ShCGs turned out to be stars. Hence, the great majority of the assumed members of these groups are galaxies.Many ShCGs, like ShCG 19 and ShCG 38 (Fig. 1), are very dense formations. Probably due to the compactness of images of the member galaxies, which on the POSS prints are almost indistinguishable from those of stars, these two groups and also some others were missed in other compact group lists, e.g. HCG list (1982). ShCGs generally consist of up to 15 members, while the distances between member galaxies are typically 3−5 times their diameters. The space density of many of ShCGs reaches about 10 4 −10 5 galaxies per Mpc 3 . The groups have a "cigar"-like, prolate spheroid configuration (Oleak et al. 1995). Numerical N-body simulations have showen that compact groups should undergo fast dynamical evolution, which will result in coalescence of member galaxies to one giant elliptical galaxy (Barnes 1985(Barnes , 1989Mamon 1986;Bode et al. 1993). It means that processes of dynamical Article published by EDP Sciences and available at http://www.edpsciences.org/aa or http://dx

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“…The results of the study of 13 ShCGs are presented in Tiersch et al (2002, Paper I), and in Tovmassian et al (2003a, Paper II, 2003b. In this paper we present the results of the study of ShCG 181, ShCG 344, ShCG 361, and ShCG 362.…”

Section: Introductionmentioning

confidence: 99%

Shakhbazian compact galaxy groups

Tovmassian¹,

Tiersch²,

Navarro³

et al. 2004

A&A

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Abstract. In 1995 we commenced a detailed spectral and photometric study of Shakhbazian compact groups. In this paper the results on groups ShCG 181, ShCG 344, ShCG 361, and ShCG 362 are presented. The redshifts of member galaxies in groups and the radial velocity dispersions, the results of the surface photometry in BVR, the profiles of the surface brightness versus semi-major axis a (or a 1/4 ) and the twisting position angle versus semi-major axis of galaxies, virial masses, luminosities and mass-to-luminosity ratios, and the crossing times of groups are given. It is shown that some members of groups are in the process of interaction. On the basis of the results obtained in this and previous works, the general properties of thirteen ShCGs are discussed.

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Shakhbazian compact galaxy groups

Cited by 26 publications

References 23 publications

Physical properties of Hickson compact groups and of the loose groups within which they are embedded

Physical properties of Hickson compact groups and of the loose groups within which they are embedded

Shakhbazian compact galaxy groups

Shakhbazian compact galaxy groups

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