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R.A. Swaters, R. Sancisi, T.S. van Albada, J.M. van der Hulst (Kapteyn Institute)
We have obtained HI and optical data for a sample of 75 late-type dwarf galaxies. The dwarfs in this sample have absolute magnitudes MB between -11 and -18, rotation velocities below 100 km s-1, andsurface brightnesses \muR between 20 and 24. We have developped a new method to derive rotation curves based on three-dimensional modelling of the data. Rotation curves have been derived for all these dwarfs, except the lowest luminosity ones, which appear supported largely by random motions.
The derived rotation curves are found to be more steeply rising than hitherto found for dwarf galaxies. Mass modelling indicates that these dwarf galaxies do not need large amounts of dark matter in the inner parts. Assuming that the contribution of the stellar disk to the rotation curve is maximal, the rotation curve out to 2 or 3 disk scale lengths can be explained almost entirely by the light. However, in some cases stellar mass-to-light ratios are needed that seem inconsistent with results from stellar population synthesis modelling. At larger radii dark matter is still needed to explain the shape of the rotation curve. Equally good fits to the rotation curves are obtained with different halo models, including Navarro-Frenk-White halos.
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The author(s) of this abstract have provided an email address for comments about the abstract: swaters@astro.rug.nl