Interactions of galaxies outside clusters and massive groups
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Date
2018-04
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Abstract
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, ρ20, 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 group galaxy interactions into four cases depending on morphology
of the target and neighbor galaxies. This study builds upon an earlier study by Park and 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 the galaxy. We report that the impact of interaction on galaxy properties is
detectable at least up to the pair separation corresponding to the virial radius of (the neighbor) galaxies. This
turns out to be mostly between 210 and 360 h−1kpc for galaxies included in our study. We report that early type
fraction for isolated galaxies with r p > rvir,nei is almost ignorant of the background density and has a very weak
density dependence for closed pairs. Star formation activity of 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.