The effects of ram-pressure stripping on the internal kinematics of simulated spiral galaxies

¹ Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria e-mail: Thomas.Kronberger@uibk.ac.at
² Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching bei München, Germany
³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany

Received: 11 January 2008
Accepted: 17 March 2008

Abstract

Aims. We investigate the influence of ram-pressure stripping on the internal gas kinematics of simulated spiral galaxies. Additional emphasis is put on the question of how the resulting distortions of the gaseous disc are visible in the rotation curve and/or the full 2D velocity field of galaxies at different redshifts.

Methods. A Milky-Way type disc galaxy is modelled in combined N-body/hydrodynamic simulations with prescriptions for cooling, star formation, stellar feedback, and galactic winds. This model galaxy moves through a constant density and temperature gas, which has parameters similar to the intra-cluster medium (ICM). We study five different configurations, in which the direction of the ram pressure on the gaseous disc varies from face-on to edge-on. Rotation curves (RCs) and 2D velocity fields of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible.

Results. We find that the appearance of distortions of the gaseous disc due to ram-pressure stripping depends on the direction of the acting ram pressure. In the case of face-on ram pressure, the distortions mainly appear in the outer parts of the galaxy in a very symmetric way. This distinction between undisturbed inner part and symmetrically disturbed outer regions is visible in both the rotation curve and the 2D velocity field. In contrast, in the case of edge-on ram pressure we find stronger distortions. In particular, a mismatch between kinematic centre and the centre of the stellar disc becomes observable. In the RC, there are basically two features visible. The RC is asymmetric as the kinematic centre does not coincide with the optical centre of the galaxy. Secondly, the outer parts of the RC are declining. The 2D velocity field also shows signatures of the interaction in the inner part of the disc. At angles smaller than 45° between the ICM wind direction and the disc, the velocity field asymmetry increases significantly compared to larger angles. Compared to distortions caused by tidal interactions, the effects of ram-pressure stripping on the velocity field are relatively low in all cases and difficult to observe at intermediate redshift in seeing-limited observations.