The effect of environment on galaxy interactions

We have investigated the effect of environment on the interaction rate of g alaxies in the local universe using data drawn from the Las Campanas Redshi ft Survey. This data set consists of galaxies inhabiting the entire range o f galactic environments, from the sparsest field to the densest clusters, t hus allowing us to study environmental variations without combining multipl e data sets with inhomogeneous characteristics. The interactions of the sam ple galaxies are characterized by the asymmetry of galactic light and the e xistence of apparent close companions, while the environment of the galaxie s is characterized both by the three-space local galaxy density and by memb ership in groups and clusters, in order to illustrate the possible differen tial influences of various environmental scales. We find that existence of apparent companions and the distortions of galaxi es are influenced differently by the surrounding environments. (1) Existenc e of the apparent close companions seems to be sensitive to both the local galaxy density and membership in association, which is sensitive to the env ironment on a larger scale than the local galaxy density. However, the sens itivity to the local density is generally low, while that to the membership is higher in some cases. In particular, galaxies with companions are disti nctively more abundant in poor clusters than in the field. On the other han d, the rich cluster/field comparison shows no environmental effects. (2) Fo r the case of the distortions, a comparison of the population ratio in the high- and low-density subsets shows that distorted galaxies are slightly mo re prevalent in the high-density environment. The effect is somewhat strong er for highly distorted galaxies than moderately disturbed ones. However, t he "membership" comparison reveals no significant effect of clustering on t he incidence of distorted galaxies. Our results show that interactions of galaxies (characterized by the distor tions of galaxies and the existence of apparent companions) are influenced by the surrounding environments. The degree of the influence varies, howeve r, depending on the measure we have used for characterizing the interaction s. The degree of the influence also varies from weak to strong interactions . Generally, the stronger interacting measures show stronger correlations w ith the environments than the weak measures, which show weak or marginal tr ends. Our results on the environmental dependence of interaction are consistent w ith the environmental variation of strong star formation investigated in ou r previous study, which used the same data set and similar analyses, suppor ting the popular understanding of the importance of interactions on the occ urrence of strong star-forming activities.