Interacting galaxies: corotating and counter-rotating systems with tidal tails

Abstract

We analyse interacting galaxy pairs with evidence of tidal features in the Sloan Digital Sky Survey Data Release 7. The pairs were selected within z < 0.1 by requiring a projected separation rp < 50 h− 1 kpc and relative radial velocity ΔV < 500 km s−1. We complete spectroscopic pairs using galaxies with photometric redshifts considering ΔVphot < 6800 km s−1, taking into account the mean photometric redshift uncertainty. We classify by visual inspection pairs of spirals into corotating and counter-rotating systems. For a subsample of non-active galactic nucleus (non-AGN) galaxies, counter-rotating pairs have larger star formation rates and a higher fraction of young, star-forming galaxies. These effects are enhanced by restricting to rp < 12 h− 1 kpc. The distributions of C, Dn(4000) and (Mu − Mr) for AGN galaxies show that counter-rotating hosts have bluer colours and younger stellar population than the corotating galaxies although the relative fractions of Seyfert, LINER, Composite and Ambiguous AGN are similar. Also, counter-rotating hosts have more powerful AGN as revealed by enhanced Lum[O III] values. The number of corotating systems is approximately twice the number of counter-rotating pairs which could be owed to a more rapid evolution of counter-rotating systems, besides possible different initial conditions of these interacting pairs.