Galaxy interactions II: High density environments
  With the aim to assess the role of dense environments in galaxy interactions,
properties we present an analysis of close galaxy pairs in groups and clusters,
obtained from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). We
identified pairs that reside in groups by cross-correlating the total galaxy
pair catalogue with the SDSS-DR7 group catalogue from Zapata et al. (2009). We
classify pair galaxies according to the intensity of interaction. We analysed
the effect of high density environments on different classes of galaxy-galaxy
interactions and we have also studied the impact of the group global
environment on pair galaxies. We find that galaxy pairs are more concentrated
towards the group centres with respect to the other group galaxy members, and
disturbed pairs show a preference to contain the brightest galaxy in the
groups. The color-magnitude relation exhibits significant differences between
pair galaxies and the control sample, consisting in color tails with a clear
excess of extremely blue and red galaxies for merging systems. In addition,
pair galaxies show a significant excess of young stellar populations with
respect to galaxies in the control sample; this finding suggests that, in dense
environments, strong interactions produce an important effect in modifying
galaxy properties. We find that the fraction of star forming galaxies decreases
toward the group centre; however, galaxy pairs show a more efficient star
formation activity than galaxies without a close companion. We have also found
that pair galaxies prefer groups with low density global environments with
respect to galaxies of the corresponding control sample. Blue, young stellar
population galaxies prefer groups within low density global environments.
