The shapes of Shakhbazian compact groups of galaxies

Abstract

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.