CLOSE PAIRS OF FIELD GALAXIES IN THE CNOC1 REDSHIFT SURVEY

A redshift sample of 545 held galaxies is used to examine how the gala xy merger rate changes with redshift and how mergers affect the observ ed properties of galaxies in close pairs. Close pairs are defined as t hose with projected separations less than 20h(-1) kpc. At a mean redsh ift of 0.33, it is found that 7.1% +/- 1.4% of galaxies are in close p hysical pairs, compared to 4.3% +/- 0.4% locally. The merger rate is e stimated to change with redshift as (1 + z)(2.8+/-0.9). These results are shown to be consistent with previous close-pair studies and provid e one of the strongest constraints to date on the redshift dependence of the merger rate. As with earlier studies, no significant difference s between the mean properties of paired and isolated galaxies are dete cted. However, using the subset of confirmed close physical pairs, tho se which appear to be undergoing interactions or mergers (based on the ir images) are found to have galaxies with strong emission lines and v ery blue rest-frame colors. In addition, these pairs have low relative velocities, increasing the likelihood that the galaxies will merge. W e interpret this as the first clear evidence of merger-induced star fo rmation occurring in held galaxies at this redshift.