HI in Early-Type Galaxies

We briefly discuss the main differences between the HI properties of luminous and low-luminosity early-type galaxies. In luminous early-type galaxies the HI is often irregularly distributed, but in a few cases regular HI disks, of low surface density, are seen. In low-luminosity galaxies, the HI is more often in a disk with high central surface densities. This suggests a different evolution of the gas in these two groups of galaxies.