Interactions of galaxies outside clusters and massive groups
  We investigate the dependence of physical properties of galaxies on small and
large scale density environment. The galaxy population consists of mainly
passively evolving galaxies in comparatively low density regions of Sloan
Digital Sky Survey (SDSS). We adopt (i) local density, $\rho_{20}$, derived
using adaptive smoothing kernel, (ii) projected distance, $r_p$, to the nearest
neighbor galaxy and (iii) the morphology of the nearest neighbor galaxy as
various definitions of environment parameters of every galaxy in our sample. In
order to detect long-range interaction effects we divide galaxy interactions
into four cases depending on morphology of target and neighbor galaxies. This
study builds upon an earlier study by Park & Choi (2009) by including improved
definitions of target and neighbor galaxies thus enabling us to better
understand the effect of "the nearest neighbor" interaction on target galaxy.
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. This turn out to be mostly between 210 and 360 $h^{-1}$kpc
for galaxies included in our study. We report that early type fraction, for
isolated galaxies with $r_p > r_{vir,nei}$ 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.
