Shakhbazian compact galaxy groups. II. Photometric and spectroscopic study of ShCG 376

The results of the redshift measurements and of the detailed surface photometry in BVR of the compact group ShCG 376 are presented. The radial velocity dispersion, the virial mass, the total luminosity, the M/L ratio, and the crossing time of the group are estimated. The group consists of eight accordant redshift spiral galaxies. Four (or possibly five) of the group members have emission-line spectra. Such morphological content and the number of emission-line galaxies are very atypical for compact galaxy groups. There are signs of interaction between some members of the group. It is suggested that the irregular shape of the brightest galaxy No. 4 is probably due to interaction with other members of the group, particularly, the emission line galaxy No. 6 with a discordant redshift (Delta v = 2600 km/s). It is speculated that the latter galaxy may be a infalling intruder to the group.Comment: accepted A&A, 7 pages, 6 figures are in separate file

On the X-ray emission of the low-mass galaxy groups

It is shown that the low-mass groups obey the $L_{x}\sim\sigma_v^{4}$ law deduced for galaxy clusters. The impression of the more shallow slope of the $L_x-\sigma_{v}$ correlation for groups is created not by enhanced X-ray emission, but by underestimation of the radial velocity dispersion of some groups.Comment: 4 pages, 2 figures, accepted in ApJ

On the Xray Luminosity - velocity dispersion relation of groups of galaxies

We analyse the Lx-sigma relation for the new Mulchaey et al. group Atlas. We find that once we take into account the possible statistical bias introduced by the cutoff in luminosity, we recover a relation which is consistent with that of clusters, ie., Lx ~ sigma^4. The larger scatter of this relation for groups of galaxies could be attributed to an orientation effect, due to which the radial velocity dispersion of groups oriented close to orthogonal to the line of sight, would be underestimated. This effect could also contribute in the direction of flattening the slope of the group Lx-sigma relation.Comment: 6 pages, Astronomy & Astrophysics, in pres

Radio emission of Shakhbazian Compact Galaxy Groups

Three hundred fifty three radio sources from the NRAO VLA Sky Survey (NVSS) (Condon et al. 1998) and the FIRST Survey (White et al. 1997}, are detected in the areas of 179 Shakhbazian Compact Groups (ShCGs) of galaxies. Ninety three of them are identified with galaxies in 74 ShCGs. Six radio sources have complex structure. The radio spectra of 22 sources are determined. Radio luminosities of galaxies in ShCGs are in general higher than that of galaxies in Hickson Compact Groups (HCGs). The comparison of radio (at 1.4 GHz) and FIR (at 60 $\mu$m) fluxes of ShCG galaxies with that of HCG galaxies shows that galaxies in ShCGs are relatively stronger emitters at radio wavelengths, while galaxies in HCGs have relatively stronger FIR emission. The reasons of such difference is discussed.Comment: 35 pages, 6 Postscript figures, ApJS in pres

Morphological and Luminosity Content of Poor Galaxy Groups

We find that the fraction of early-type galaxies in poor groups (containing from 4 to 10 members) is a weakly increasing function of the number of the group members and is about two times higher than in a sample of isolated galaxies. We also find that the group velocity dispersion increases weakly with the fraction of early-type galaxies. Early-type galaxies in poor groups are brighter in the near-infrared with respect to isolated ones by 0.75 mags (in K) and to a lesser degree (by 0.5 mags) also in the blue. We also find early-type galaxies in groups to be redder than those in the field. These findings suggest that the formation history for early-type galaxies in overdense regions is different from that of in underdense regions, and that their formation in groups is triggered by merging processes.Comment: 5 pages, 3 figures, ApJ Lett. in pres

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

On the nature of the hard X-ray sources SWIFTJ1907.3-2050, IGRJ12123-5802 and IGRJ19552+0044

The INTEGRAL and Swift hard X-ray surveys have identified a large number of new sources, among which many are proposed as Cataclysmic Variables (CVs). Here we present the first detailed study of three X-ray selected CVs, Swift J1907.3-2050, IGRJ12123-5802, and IGRJ19552+0044 based on XMM-Newton, Suzaku, Swift observations and ground based optical and archival nIR/IR data. Swift J1907.3-2050 is highly variable from hours to months-years at all wavelengths. No coherent X-ray pulses are detected but rather transient features. The X-ray spectrum reveals a multi-temperature optically thin plasma absorbed by complex neutral material and a soft black body component arising from a small area. These characteristics are remarkably similar to those observed in magnetic CVs. A supra-solar abundance of nitrogen could arise from nuclear processed material from the donor star. Swift J1907.3-2050 could be a peculiar magnetic CV with the second longest (20.82 h) binary period. IGRJ12123-5802 is variable in the X-rays on a timescale of ~7.6 h. No coherent pulsations are detected, but its spectral characteristics suggest that it could be a magnetic CV of the Intermediate Polar (IP) type. IGRJ19552+0044 shows two X-ray periods, 1.38 h and 1.69 h and a X-ray spectrum characterized by a multi-temperature plasma with little absorption.We derive a low accretion rate, consistent with a CV below the orbital period gap. Its peculiar nIR/IR spectrum suggests a contribution from cyclotron emission. It could either be a pre-polar or an IP with the lowest degree of asynchronism.Comment: Accepted for publication in MNRAS. 14 pages, 11 figures, 5 table