Peculiar motions of Abell clusters in compact groups.
Abstract
An estimator (measure) of the observed pair redshift velocity variance, E(σ^2^_V_) = σ^2^_R_1/2σ^2^_T_ is evaluated from the observed separation vectors of Abell clusters, resolved into a component in (a) the redshift direction, R, and (b) the plane of the sky, T = (x^2^+y^2^)^1/2^, analysed with allowance for edges in the survey regions. Several statistical samples are studied, including rich groups containing five or more clusters identified individually by a procedure that applies linkage of separation vectors of length <= 42 Mpc (H_0_= 100 km s^1^ Mpc^1^) followed by a 3 σ statistical test on consecutive differences of ordered coordinates. Compact groups of clusters with clustercluster separations ~10 Mpc each have an observed rms pair redshift velocity dispersion σ_v_~2100 km s^1^ (above zero at the 2 σ,98 per cent confidence level), corresponding to a physical rms redshift velocity dispersion of clusters with respect to the group barycentre σ_v0_~ 1200 km s^1^, suggestive of large peculiar motions. The velocity dispersion is smaller for looser groups, and σ_v_~ 0 for groups with clustercluster separations ~21 Mpc (the scalelength of the twopoint correlation function of Abell clusters), consistent with unperturbed Hubble flow, small infall, and/or small peculiar motions. The derived rms error of E(σ^2^_v_) for the two identified rich compact groups, ~0.5 E(σ^2^_v_), and for the other samples, is the quadrature sum of the contributions by the intrinsic uncertainty of the estimator, errors in cluster redshifts, anisotropic geometrical structure, ad the enhancement of cluster richness counts by projected neighbours on the sky.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 January 1992
 DOI:
 10.1093/mnras/254.1.67
 Bibcode:
 1992MNRAS.254...67R
 Keywords:

 Compact Galaxies;
 Galactic Clusters;
 Red Shift;
 Velocity Distribution;
 Gravitational Effects;
 Hubble Constant;
 Spatial Distribution;
 Virial Theorem;
 Astrophysics