We propose that the giant HI ring recently discovered by HIPASS for S0 galaxy NGC 1533 is formed by unequal-mass merging between gas-rich LSB (low surface brightness: "ghost'') galaxies and HSB disks. The NGC 1533 progenitor HSB spiral is transformed into a barred S0 during merging and the outer HI gas disk of the LSB is transformed into the giant HI ring. We also discuss two different possibilities for the origin of isolated star-forming regions ("ELdot'' objects) in the giant gas ring.
Proceedings of the International Astronomical Union Symposium S217: Recycling Intergalactic and Interstellar Matter, Sydney, New South Wales, Australia, 14-17 July 2003 / Pierre-Alain Duc, Jonathan Braine and Elias Brinks (eds.),