Interactions of Galaxies outside Clusters and Massive Groups

We investigate the dependence of physical properties on small and large scale density environ-ment. The galaxy population consists of mainly passively evolving galaxies in comparatively low density regions of Sloan Digital Sky Survey (SDSS). The environment is defined by (i) local density using adaptive smoothing kernel, (ii)projected distance, rp, to the nearest neigh-bor and (iii) the morphology of the nearest neighbor. In order to detect long-range interaction effects we divide galaxy interactions into four cases depending on morphology of target and neighbor galaxies. We report that the impact of interaction on galaxy properties is detectable at least out to the pair separation corresponding to the virial radius of (the neighbor) galaxies in our sample, which is mostly between 210 and 360 h−1kpc. We show that early type fraction, for isolated galaxies with rp> rvir,nei are almost ignorant of the background density and, has a very weak density dependence for closed pairs. Star formation activity of a a galaxy is found to be crucially dependent on neighbor galaxy morphology. We find star formation activity parameters and structure parameters of galaxies to be independent of the large scale background density. We also exhibit that changing the absolute magnitude of the neighbor galaxies does not affect significantly the star formation activity of those target galaxies whose morphology and luminosities are fixed