Extended HI disks in dust-lane elliptical galaxies

Abstract

We present the results of HI observations of five dust-lane ellipticals with the Australia Telescope Compact Array. Two galaxies (NGC 3108 and NGC 1947) are detected, and sensitive upper limits are obtained for the other three. In the two detected galaxies, the HI is distributed in a regular, extended and warped disk-like structure of low surface brightness. Adding data from the literature, we find that several more dust-lane ellipticals have regular HI structures. This HI is likely to be a remnant of accretions/mergers which took place a considerable time ago, and in which a significant fraction of the gas survived to form a disk. The presence of regular HI structures suggests that some mergers lead to galaxies with extended low surface brightness density gas disks. These gas disk will evolve very slowly and these elliptical galaxies will remain gas rich for a long period of time. (abridged)