Discordant redshifts in compact groups

This paper addresses the long standing question of discordant redshifts in compact groups. We have used an homogenous catalogue of 173 compact groups selected by an automated procedure to objectively predict the fraction of discordant redshifts with high statistical accuracy, and then applied these results to the sample of 92 compact groups in Hickson’s revised catalogue. Our results confirm that projection effects alone can account for the high incidence of discordant redshifts in compact groups. We have also examined the spatial distribution of discordant galaxies in Hickson’s compact groups. Contrary to previous studies, we find that there is no evidence for central concentration of discordant galaxies.