The consequences of ram pressure stripping on the Virgo cluster spiral galaxy NGC 4522

Abstract

New H-alpha Fabry-Perot interferometer observations of the Virgo cluster spiral galaxy NGC 4522 are presented. A velocity field up to a radius of 60'' was obtained. The observed rotation curve is symmetric. It is not perturbed in the inner disk. For radii >50'' it shows a solid body rotation. We compare these data with a numerical model which includes the effects of ram pressure stripping. The model can reproduce the main characteristics of the H-alpha emission distribution and velocity field. We therefore conclude that the stripping event which caused the HI deficiency and the distorted H-alpha distribution and velocity field has been due to ram pressure. The closest passage of the galaxy to the cluster center is estimated to be approx. 6.5 10^8 yr ago. The observed recent star formation is due to the re-accretion of gas clouds which were accelerated to velocities below the escape velocity during the stripping event. Furthermore, the gas which is located at radii >60'' is part of an asymmetric expanding ring of gas clouds. A substantial part of these clouds is located above the disk plane. We predict the HI gas distribution and velocity field as it would be observed by deep 21 cm observations.