Extended H I disks in dust lane elliptical galaxies

We present the results of H I observations of five dust lane elliptical galaxies 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 H I is distributed in a regular, extended, and warped disklike structure of low surface brightness. Adding data from the literature, we find that several more dust lane elliptical galaxies have regular H I structures. This H I is likely to be a remnant of accretions and/or mergers that took place a considerable time ago and in which a significant fraction of the gas survived to form a disk. The presence of regular H I structures suggests that some mergers lead to galaxies with extended low surface brightness density gas disks. These gas disks will evolve very slowly, and these elliptical galaxies will remain gas-rich for a long period of time. One of the galaxies we observed ( NGC 3108) has a very large amount of neutral hydrogen (M-H I = 4.5x10(9) M-circle dot; M-H I/L-B similar to 0.09), which is very regularly distributed in an annulus extending to a radius of similar to6 R-eff. The kinematics of the H I distribution suggest that the rotation curve of NGC 3108 is at out to at least the last observed point. We estimate a mass-to-light ratio of M/L-B similar to 18 M-circle dot/L-B,(circle dot) at a radius of similar to6 R-eff from the center. Several of the galaxies we observed have an unusually low gas-to-dust ratio M-H I/M-dust, suggesting that their cold interstellar medium, if present as expected from the presence of dust, may be mainly in molecular rather than atomic form.