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G.R. Meurer (JHU), K.C. Freeman (MSSSO), J. Bland-Hawthorn (AAO), M.R. Jones (STScI), P.M. Knezek (JHU), R.J. Allen (STScI)
NGC 2915 is a spectacular Dark Matter dominated galaxy having an HI disk and HI spiral arms extending out to a radius of 15 Kpc. However, in optical continuum emission it is a relatively nondescript Blue Compact Dwarf galaxy, with an optical radius of only ~ 3Kpc. No stars were known to exist beyond this radius. We present deep H\alpha imaging obtained with the 3.9m AAT and the Taurus Tunable Filter, revealing for the first time faint HII regions at projected radii of 3 to 6 Kpc. Deep spectroscopy with the ANU 2.3m confirm that two of the HII regions are indeed within NGC 2915. The integrated surface brightness and mass density of the associated newly formed stars are estimated. We also present high resolution spectra of a background galaxy which are used to constrain the Na I and Ca II column within NGC 2915 and towards a sight line passing near the ridge of one of the HI spiral arms.
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