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A. D. Bolatto, A. Leroy, J. D. Simon, L. Blitz (U.C Berkeley, Department of Astronomy)
We present the first results from a program to measure the inner rotation curves of dark matter--dominated dwarf galaxies by using the BIMA Array to map their CO velocity fields. The data for the dwarf SB(s)c galaxy NGC 4605 indicate that its rotation curve rises almost linearly out to an angular distance of 60\arcsec, corresponding to a spatial scale of about 1.5 kpc. Archival HI data from the VLA and infrared images from the 2MASS survey are also used to determine the mass distribution in the galaxy over a large range of radii and show that dark matter dominates the potential of the galaxy as far into the center as is resolved by the CO data. The velocity field of this galaxy is also seen to be quite regular with little evidence for non--circular motions in the CO. We compare our results with the predictions of Cold Dark Matter (CDM) simulations, which imply that there is a universal density profile followed by all dark matter halos with a central density cusp that varies as r-1 or steeper. Previous attempts to test this prediction using HI rotation curves of dark matter--dominated galaxies have been inconclusive, because of the low spatial resolution of the observations. Our CO observations have an angular resolution of ~5\arcsec, and should therefore be minimally affected by beam smearing. The data show that the rotation of NGC 4605 is difficult to reconcile with a density cusp as steep as predicted by CDM simulations. We are currently carrying out a systematic survey to locate other suitable dwarf galaxies for this type of study.