group radius.

The velocity distributions are consistent for the two samples. The velocity dispersion distributions of the subsamples agree at the 99% confidence level for $N=3$ and at the 49% confidence level for $N \geq 4$. Figures \[fig:isovel\]a and \[fig:isovel\]b show the velocity distributions for groups with $N=3$ and groups with $N \geq 4$, respectively. We note, however, that the subsamples of RSCG’s in these comparisons are small. There are 11 groups with $N \geq 4$ and $\Upsilon > 3$, 19 groups with $N \geq 4$ and $\Upsilon < 3$, 53 groups with $N=3$ and $\Upsilon > 3$, and only 6 groups with $N=3$ and $\Upsilon < 3$.

We visually examine regions around the 48 RSCG’s with $\Upsilon > 3$ and $cz > 2300\ {\rm km\ s}^{-1}$ using Digitized Sky Survey images. About 1/3 of these groups have faint galaxies (with $m \lesssim m_{1}+3$) in their isolation annuli without measured redshifts. In other words, at least 30 of the RSCG’s are isolated according to Hickson’s criteria. However, this apparent isolation is not a good predictor of the environment of compact systems and contains no information about the physics of the systems.

Environments of Compact Groups
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Previous studies of the 