Galactic recycling: The HI ring around NGC 1533

Abstract

We report the discovery of a new HI ring around the SO 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 Hα emission associated with the SE part of the ring only. The Hα is in the form of a few very small isolated emission line regions. The large HI velocity dispersions (up to 30 km s-1) and velocity gradients (up to 50 km s-1 kpc-1) in this region indicate the Hα emission could be due to star formation triggered by clouds c..