Morphological classification /revised RS/ of Abell clusters in D less than or equal to 4 and an analysis of observed correlations

Abstract

We present a catalog of revised Rood-Sastry (RS) types for the 276 Abell clusters in distance class &lt;4 obtained from the Palomar Observatory Sky Survey plate collection at KPNO. Also included are the Hubble morphological types of the three brightest galaxies and the separations between them. Separations between binaries (which are counted as single galaxies) among the three brightest galaxies are also given; notation of other binaries are also listed. Abell counts (N<SUB>A</SUB>), Bautz-Morgan (BM) type, redshifts, and line-of-sight velocity dispersions ( ) are also tabulated. Based on systematic gradations in data profiles and galactic content of observed clusters, and on N-body simulations, we tentatively suggest the following schematic as a possible progression of cluster evolution: <P />C / \ / \ I ------F &lt; &gt; B ------ cD \ / \ / L <P />Among the results of observed correlations are: (1) Most of the F ("flat") types are composed of two or three individual subclusters. (2) cD types are mostly BM I, I-II, and II, B types are nearly uniformly distributed throughout the BM types, and C, L, F, and I types are most often MM III. (3) The morphological types of the three brightest galaxies for B, C, and L types are similar to one another, while those of F and I types are similar to one another and dissimilar to those of the B, C, and L types; cD types also have the fewest binaries. (4) The average separation between the first and second brightest galaxies (<SUP>-</SUP>r<SUB>12</SUB>) and between the first and third brightest galaxies (<SUP>-</SUP>r<SUB>13</SUB>) are smallest for C and L types (&lt;1 Mpc, H<SUB>0</SUB> = 50 km s<SUP>-1</SUP> Mpc<SUP>-1</SUP>) and are largest for F and I types (∼1-2 Mpc). (5) In cD clusters, <SUP>-</SUP>r<SUB>12</SUB> is larger by ∼0.5 Mpc in a larger redshift interval at 99.9% level (t test), which may be direct evidence for dynamical evolution (mass segregation); this is probably not an effect of projection bias because the second brightest galaxy is, in the great majority of cases, E, E/SO or SO and not S, as expected for field contamination. (6) For cD, B, C, and L types, previously identified as relaxed systems or σ<SUB>vls</SUB> ∝ N<SUP>0.7</SUP><SUB>A</SUB>; these results are understandable within the context of the theoretical formula for relaxation time. Several observational selection effects, especially "Malmquist" biases, in the sample of clusters are also discussed; these are usually a function of redshift.