Extended H [CSC]i[/CSC] Disks in Dust Lane Elliptical Galaxies

Abstract

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 (NGC3108) has a very large amount of neutral hydrogen (MH i =4.5 ? 109M?; MH i/LB ? 0.09), which is very regularly distrib-galaxies will remain gas-rich for a long period of time. One of the galaxies we observed (NGC3108) has a very large amount of neutral hydrogen (MH i =4.5 ? 109M?; MH i/LB ? 0.09), which is very regularly distrib- uted in an annulus extending to a radius of ?6 Reff. The kinematics of the H i distribution suggest that the large amount of neutral hydrogen (MH i =4.5 ? 109M?; MH i/LB ? 0.09), which is very regularly distrib- uted in an annulus extending to a radius of ?6 Reff. The kinematics of the H i distribution suggest that the rotation curve ofNGC3108 is flat out to at least the last observed point. We estimate a mass-to-light ratio of uted in an annulus extending to a radius of ?6 Reff. The kinematics of the H i distribution suggest that the rotation curve ofNGC3108 is flat out to at least the last observed point. We estimate a mass-to-light ratio of M/LB ? 18 M?/LB,? at a radius of ?6Reff from the center. Several of the galaxies we observed have an unusually low gas-to-dust ratio MH i/Mdust, suggesting that their cold interstellar medium, if present as M/LB ? 18 M?/LB,? at a radius of ?6Reff from the center. Several of the galaxies we observed have an unusually low gas-to-dust ratio MH i/Mdust, suggesting that their cold interstellar medium, if present as expected from the presence of dust, may be mainly in molecular rather than atomic form. unusually low gas-to-dust ratio MH i/Mdust, suggesting that their cold interstellar medium, if present as expected from the presence of dust, may be mainly in molecular rather than atomic form.