Galaxy interactions in SDSS-DR7: Analysis of the major and minor mergers

MESA, VALERIA; MA. SOL ALONSO; DIEGO GARCÍA LAMBAS; ANA LAURA O'MILL

Buenos Aires

Workshop; Second Workshop on Numerical and Observational Astrophysics From the First Structures to the Universe Today; 2011

IAFE

We present an analysis of close galaxy pairs (rp < 25 kpc h-1 and ΔV < 350 km s-1) selected from the SDSS-DR7 within redshift z<0.1. By mean of visual inspection of SDSS images we quantify the strength of the interaction through a classification of thegalaxies 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 studystar formation activity through colors, the 4000 Å break, and star formation rates.We find that 10% of the pairs are classified as M. These systems show an excess of young stellar populations as inferred from the Dn(4000) spectral index, colors, and star formation rates of the member galaxies, an effect which we argue, is directly relatedto 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 longertime-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 theevolution 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.