da Costa'
title: Compact Group Selection From Redshift Surveys
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Introduction
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Compact groups are the densest known systems of galaxies in the universe. Rose (1977) and Hickson (1982) made the first large-scale, systematic searches for dense systems on the sky. Subsequent studies of the properties and environments of Hickson’s 100 Compact Groups indicate that they are probably not dynamically simple, isolated systems.

Here, for the first time, we select compact systems from a complete, magnitude-limited redshift survey. We select groups based on physical extent, rather than angular size. This approach eliminates some of the systematic biases intrinsic to identification of systems on the sky. Because we begin with a complete, magnitude-limited survey we can model the residual selection effects from first principles. We use the redshifts of galaxies surrounding our compact groups to explore the embedding of the Redshift Survey Compact Groups (RSCG’s, hereafter) in their environments.

Hickson’s work sparked debates about the physics of compact groups. The existence of compact groups is a challenge for dynamical models because their measured crossing times are generally much smaller than the Hubble time. Numerical simulations indicate that compact group galaxies merge to form bright elliptical galaxies on timescales comparable to the 