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 (SDSS-DR7). The pairs were selected within z < 0.1 by requiring a projected separation r p < 50 h −1 kpc and relative radial velocity ∆V < 500 km s −1 . We complete spectroscopic pairs using galaxies with photometric redshifts considering ∆V phot < 6800 km s −1 , taking into account the mean photometric redshift uncertainty. We classify by visual inspection pairs of spirals into co-rotating and counter-rotating systems. For a subsample of 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 r p < 12 h −1 kpc. The distributions of C, D n (4000) and (M u − M r ) for AGN galaxies show that counter-rotating hosts have bluer colours and younger stellar population than the co-rotating 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[OIII] values. The number of co-rotating systems is approximately twice the number of counter-rotating pairs which could be owed to a more rapid evolution of counterrotating systems, besides possible different initial conditions of these interacting pairs.

On the nature of small galaxy systems

“…This tendency is stronger for galaxy pairs highlighting that the photometric data described in section 2 is useful to complete the sample of close pairs. These results are in agreement with the work of Mesa et al (2014) who identify close tidal pairs by looking for photometric companions of spectroscopic galaxies. After a visual classification, these authors found that more than 60% of spectro-photometric pairs have dis- torted morphologies with features such as tidal tails and bridges or clear signs of fusion in process.…”

Visiting two objects in the field of the ring galaxy HRG 2302

“…Based on these spectroscopic results, the projected separation of r p ∼ 20 h −1 kpc and the radial velocity difference of ΔV ∼ 96 km s −1 , we confirm that the two galaxies are an interacting pair. These values agree well with some recent statistical work on the construction of galaxy pair catalogs, see Mesa et al (2014) and reference therein. In this recent paper, the authors discuss interacting galaxy pairs with evidence of tidal features in the Sloan Digital Sky Survey data release 7 (SDSS-DR7) for z < 0.1 with r p < 50 h −1 kpc and ΔV < 500 km s −1 .…”

Satellites and central galaxies in SDSS: the influence of interactions on their properties

“…We have used this method previously with excellent results (e.g. Alonso et al 2007;Lambas et al 2012;Mesa et al 2014). This technique also allows us to clean the sample of galaxies immersed in groups, undetected by the software due the galaxies only have photometric information.…”

“…Throughout the history of the Universe, galaxy-galaxy interactions play a crucial role in galaxy formation and evolution according to the hierarchical model of structure formation, by linking together star formation processes with galaxies growth (Sol Alonso et al 2006;Woods & Geller 2007;Ellison et al 2010;Lambas et al 2003Lambas et al , 2012Mesa et al 2014). On the observational side, several works (e.g.…”