THE SURFACE-DENSITY PROFILES AND LENSING CHARACTERISTICS OF HICKSON COMPACT-GROUPS OF GALAXIES

A statistical method is developed to infer the typical density profile s of poor galaxy systems without resort to binning of data or assuming a given center to each system. The method is applied to the accordant redshift quartets in Hickson compact groups (HCGs). The distribution of separations in these groups is consistent with a unique generalized and modified Hubble surface density profile, with best-fit asymptotic slope beta=1.4 and core radius R(c) 18 h(-1) kpc, although a King pro file (beta=1) is also consistent with the data (with R(c) 6 h(-1) kpc) . These distributions are more concentrated than what has been determi ned previously for these groups. HCGs are unlikely to act as strong gr avitational lenses, but analogous systems 5-10 times more distant shou ld produce a nonnegligible fraction of giant arcs.