We report the discovery of a new HI ring around the S0 galaxy NGC 1533. The ring orbits at a radius of 35 kpc, well outside the optical extent of the galaxy. We have conducted N-body/SPH numerical simulations to show this HI ring could be the merger remnant of a tidally destroyed galaxy. We find no optical component associated with the HI ring. However, observations hint at H-alpha emission associated with the SE part of the ring only. The H-alpha is in the form of a few very small isolated emission line regions. The large HI velocity dispersions (up to 30 km/s) and velocity gradients (up to 50 km/s kpc-1) in this region indicate the H-alpha emission could be due to star formation triggered by clouds colliding within the ring.
Astrophysics and space science library: The IGM/galaxy connection: the distribution of baryons at z=0: proceedings of a meeting held at Boulder, Colorado, United States, 08-10 August 2003 / Jessica L. Rosenberg and Mary E. Putman (eds.),
Vol. 281, pp. 223