Galaxy interactions

Abstract

Aims. We study galaxy pair samples selected from the Sloan Digital Sky Survey (SDSS-DR7) and we perform an analysis of minor and major mergers with the aim of investigating the dependence of galaxy properties on interactions. Methods. We build a galaxy pair catalog requiring r p < 25 kpc h −1 and ΔV < 350 km s −1 within redshift z < 0.1. By visual inspection of SDSS images we remove false identifications and we classify the interactions into three categories: pairs undergoing merging, M; pairs with evident tidal features, T ; and non disturbed, N. We also divide the pair sample into minor and major interactions according to the luminosity ratio of the galaxy members. We study star formation activity through colors, the 4000 Å break, and star formation rates. Results. We find that ∼10% of the pairs are classified as M. These systems show an excess of young stellar populations as inferred from the D n (4000) spectral index, colors, and star formation rates of the member galaxies, an effect which we argue is directly related to the ongoing merging process. We find ∼30% of the pairs exhibiting tidal features (T pairs) with member galaxies showing evidence of old stellar populations. This can be associated either to the disruptive effect of some tidal interactions, or to the longer time-scale of morphological disturbance with respect to the bursts of the tidal induced star formation. Regardless of the color distribution, we find a prominent blue peak in the strongest mergers, while pairs with tidal signs under a minor merger show a strong red peak. Therefore, our results show that galaxy interactions are important in driving the evolution of galaxy bimodality. By adding stellar masses and star formation rates of the two members of the pairs, we explore the global efficiency of star formation of the pairs as a whole. We find that, at a given total stellar mass, major mergers are significantly more efficient (a factor ≈2) in forming new stars, with respect to both minor mergers or a control sample of non-interacting galaxies. We conclude that the characteristics of the interactions and the ratio of luminosity galaxy pair members involved in a merger are important parameters in setting galaxy properties.

Supernovae and their host galaxies – II. The relative frequencies of supernovae types in spirals

“…We define four categories of SN host disturbances: normal (hosts without any visible disturbance in their morphological structure), perturbed (hosts with visible morphological disturbance, but without long tidal arms, bridges, or destruction of spiral patterns), interacting (hosts with obvious signs of galaxy-galaxy interaction), merging (hosts with evidence of an ongoing merging process; see e.g. Lambas et al 2012), and postmerging/remnant (single galaxies that exhibit signs of a past interaction, with a strong or already relaxed disturbance, see e.g. Ellison et al 2013 andLotz et al 2008, respectively).…”

Galaxy pairs in the Sloan Digital Sky Survey – VIII. The observational properties of post-merger galaxies

“…By combining the imaging and spectroscopic samples, it has been possible to tackle many aspects of galaxy mergers with unparalleled statistics. Samples of either close spectroscopic pairs, or morphologically classified mergers have been used to investigate the impact of galaxy interactions on colours (Ellison et al 2010;Patton et al 2011;Alonso et al 2012;Lambas et al 2012), star formation rates (Nikolic, Cullen & Alexander 2004;Alonso et al 2006;Li et al 2008a;Scudder et al 2012b;Patton et al 2013), metallicity (Michel-Dansac et al 2008;Ellison et al 2008;Reichard et (Hwang et al 2010(Hwang et al , 2011Ellison et al 2013) and nuclear activity (Alonso et al 2007;Woods & Geller 2007;Li et al 2008b;Ellison et al 2008Ellison et al , 2011Rogers et al 2009;Darg et al 2010;Liu, Shen & Strauss 2012;Sabater et al 2013).…”

Close Neighbors of Markarian Galaxies. II. Statistics and Discussions

“…On the other hand, effect of large-scale environment was considered small, but non-zero in [22]. It is mostly assumed that major mergers are more effective in triggering starbursts (also AGNs), than minor ones [4,5,14,16,23,24,25,26]. At the same time, minor mergers occur more frequently, and partially can explain triggered SF in early-type galaxies, e.g.…”

“…Although these parameters are correlated with each other at first approximation, see e.g. [26,34], they can bias the pair statistics in different ways because of correlation with large-scale environment, e.g. [20], possible effects on morphological classification, e.g.…”