Internal kinematics of modelled interacting disc galaxies

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany-/-Abstract. We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of discgalaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, andgalactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows theprocedure applied to observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys disturb the velocity fields significantly and hence the RCs of the interacting galaxies,leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are significantly risingor falling profiles in the direction of the companion galaxy and pronounced bumps in the RCs. In addition, tidaltails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshiftgalaxies, on which we focus our investigations. We use a quantitative measure for the asymmetry of rotation curvesto show that the appearance of these distortions strongly depends on the viewing angle. We also find in this waythat the velocity fields settle back into relatively undisturbed equilibrium states after unequal mass mergers andfly-bys. About 1 Gyr after the first encounter, the RCs show no severe distortions anymore. These results areconsistent with previous theoretical and observational studies. As an illustration of our results, we compare oursimulated velocity fields and direct images with rotation curves from VLT/FORS spectroscopy and ACS imagesof a cluster at z=0.53 and find remarkable similarities.Key words. Galaxies: kinematics and dynamics - Galaxies: interactions - Methods: numerical