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Session 68 - Disk Galaxies.
Display session, Wednesday, January 15
Metropolitan Ballroom,
Like most spirals, Sa's have been found to need little dark matter within their optical extent to explain observed rotation curves. However, previous studies by (e.g. Broeils 1992, 1995) have indicated that unlike later--type spirals, Sa galaxies may need little to no dark matter beyond the optical disk. Since the HI distribution typically extends well beyond the optical edge, it is ideal for measuring the dark matter content at large distances from the center. As part of a study of the dark matter content as well as the gas and stellar kinematics of Sa galaxies, we have obtained HI synthesis maps of 9 gas--rich Sa's, a subsample of 22 Sa galaxies for which we have obtained optical emission and absorption line rotation curves. All of the galaxies are non--interacting but 19 out of 22 have some kinematic peculiarities and and two of them (NGC 4138 and NGC 3626) have extended counter--rotating stellar and/or gas disks. The objects were observed typically for 8 hours with the VLA in C or D array, resulting in data sets with a channel separation of 20 km s^-1 channels^-1. The HI rotation curves, derived using tilted ring models, will be combined with optical images obtained at the Kitt Peak 0.9m telescope and optical rotation curves obtained with the Double Spectrograph on the Palomar 5m telescope in order to model the amount of dark matter in these galaxies. We will present the HI distribution and velocity fields of our sample, as well as the distributions of stellar and dark matter derived from the mass modeling.
