IMPACT OF NEIGHBORS IN SDSS GALAXY PAIRS

Abstract

How galaxies are a ected by their neighboring galaxies during galaxy-galaxy interactions is a long-standing question. We investigate the role of neighbors in galaxy pairs based on the SDSS data release 7and the KIAS value-added galaxy catalog. Three groups of galaxies are identi ed: (a) galaxies with anearly-type neighbor, (b) with a late-type neighbor, and (c) isolated ones with no neighbor. We comparetheir UV + optical colors and H emission as indicators of the recent star-formation rate (SFR). Giventhat galaxies show systematic di erences in SFR as functions of morphology, luminosity, and large-scaleenvironments, we construct a control sample in which the galaxies have the same conditions (in terms ofmorphology, luminosity, and large-scale environment) except for the neighbor’s properties (i.e., morphol-ogy, mass, and distance). The results are as follows. (1) Galaxies with a late-type companion demonstratemore enhanced SFR than those with an early-type companion. (2) Galaxies with an early-type neighborshow NUV- and u-band derived SFRs that are even lower than that of isolated galaxies, while they havesimilar or slightly higher H -based SFR compared to isolated ones.Key words: galaxies: evolution | galaxies: general | galaxies: interactions | galaxies: star formation1. INTRODUCTIONThe galaxy-galaxy interaction is one of the key factorsin galaxy evolution. However, exactly how a galaxyis a ected by its neighbors remains an open question.Galaxy pairs are important tools for the study of galaxyinteractions, as we can easily regard any change in thegalaxy’s properties as being caused by interaction witha companion. The advent of large survey such as theSloan Digital Sky Survey (SDSS; York et al. 2000) hasenabled the exclusion of the undesirably peculiarty ofindividual galaxies.Park et al. (2008) and Park & Choi (2009) showedthat SDSS galaxies statistically resemble their neighbor-ing galaxies’ properties, including star formation rates(SFR). Meanwhile, it has been reported in many pre-vious studies that star formation activity in close pairgalaxies is increased by tidal force (Barton et al. 2000;Nikolic et al. 2004; Ellison et al. 2008). In this study, wewill clarify the impact of neighbors on the SFR in com-parison with a non-pair control sample, and reconcilethe previous studies on galaxy pairs.2. METHODOLOGYOur galaxy sample is based on the Korea Institute forAdvanced Study Value-Added Galaxy Catalog (KIAS