Minor mergers and their impact on the kinematics of galaxy discs

¹ GÉPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
² Department of Physics, Indian Institute of Science, Bangalore 560012, India

Abstract

By means of N-body simulations, we have investigated the impact of minor mergers on the angular momentum content and kinematical properties of a disc galaxy. Our simulations cover a range of initial orbital characteristics and the system consists of a massive galaxy with a bulge and a stellar disc merging with a much less massive gasless companion. Our results show that: (1) during the process of merging, the disc of the primary galaxy becomes kinematically hotter and thicker; (2) its specific angular momentum always decreases, independent of the orbit or morphology of the satellite galaxy; (3) the decrease in the rotation velocity of the primary galaxy is accompanied by a change in the anisotropy of the stellar orbits, which becomes increasingly radially dominated as the merger advances; (4) the radial velocity dispersion increases at all radii, but in particular in the outermost regions; (5) at the same time, the transverse velocity decreases throughout the whole disc, except in the inner region, where the constribution of bulge stars leads to an increase of σ_t.