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A. J. Remijan (U. Illinois), R. J. Lavery, M. D. Reed (Iowa State U.)
We report on our continuing program of identifying distant collisional ring galaxies in red WFPC2 images obtained from the Hubble Space Telescope Archives. Collisional ring galaxies have organized regions of enhanced star formation that make them readily identifiable at high redshift with the image resolution of the HST. The aim of this program is to produce a catalog of distant ring galaxies to be used in a redshift survey to directly measure the exponent, \textit{m}, in the parameterization of the interaction/merger rate as a function of \textit{z}, \textit{(1 + z)}m.
To date, we have visually scanned approximately 100 random WFPC2 fields and have identified between 15 and 20 excellent collisional ring galaxy candidates. We will present our comparison of the photometric and physical properties of our updated sample with those of nearby ring galaxies, which has allowed estimated redshifts to be determined for our sample. The large majority of these galaxies have estimated redshifts less than 1.
We find that the number of candidate ring galaxies we have identified is much higher than that predicted by low values of \textit{m} (0 or 1). In fact, we can rule these low values of \textit{m} at greater than the 3 sigma level. This suggests a very steeply increasing galaxy interaction rate with redshift out to \textit{z} = 1. We will compare our value for \textit{m} with previous determinations made using other methods.
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The author(s) of this abstract have provided an email address for comments about the abstract: aremijan@astro.uiuc.edu