AHubble Space TelescopeSnapshot Survey of Dynamically Close Galaxy Pairs in the CNOC2 Redshift Survey

We compare the structural properties of two classes of galaxies atintermediate redshift: those in dynamically close galaxy pairs, and those whichare isolated. Both samples are selected from the CNOC2 Redshift Survey, andhave redshifts in the range 0.1 < z <0.6. Hubble Space Telescope WFPC2 imageswere acquired as part of a snapshot survey, and were used to measure bulgefraction and asymmetry for these galaxies. We find that paired and isolatedgalaxies have identical distributions of bulge fractions. Conversely, we findthat paired galaxies are much more likely to be asymmetric (R_T+R_A >= 0.13)than isolated galaxies. Assuming that half of these pairs are unlikely to beclose enough to merge, we estimate that 40% +/- 11% of merging galaxies areasymmetric, compared with 9% +/- 3% of isolated galaxies. The difference iseven more striking for strongly asymmetric (R_T+R_A >= 0.16) galaxies: 25% +/-8% for merging galaxies versus 1% +/- 1% for isolated galaxies. We find thatstrongly asymmetric paired galaxies are very blue, with rest-frame B-R colorsclose to 0.80, compared with a mean (B-R)_0 of 1.24 for all paired galaxies. Inaddition, asymmetric galaxies in pairs have strong [OII]3727 emission lines. Weconclude that close to half of the galaxy pairs in our sample are in theprocess of merging, and that most of these mergers are accompanied by triggeredstar formation.