2010MNRAS.404.2061E

NGC 2915 is a nearby blue compact dwarf with the Hi properties of a late-type spiral. Its large, rotating Hi disc (extending out to R ∼ 22 B-band scalelengths) and apparent lack of stars in the outer Hi disc make it a useful candidate for dark matter studies. New Hi synthesis observations of NGC 2915 have been obtained using the Australia Telescope Compact Array. These data are combined with high-quality 3.6-µm imaging from the Spitzer Infrared Nearby Galaxies Survey. The central regions of the Hi disc are shown to consist of two distinct Hi concentrations with significantly non-Gaussian line profiles. This discredits the idea of a massive Hi bar constituting the inner Hi morphology. We fit a tilted ring model to the Hi velocity field to derive a rotation curve. This is used as input for mass models that determine the contributions from the stellar and gas discs as well as the dark matter halo. The galaxy is dark matter dominated at nearly all radii. At the last measured point of the rotation curve the total mass to blue light ratio is M_tot/L_B ∼ 140M_☉/L_B, making NGC 2915 one of the darkest galaxies known. We show that the stellar disc cannot account for the steeply rising portion of the observed rotation curve. The best-fitting dark matter halo is a pseudo-isothermal sphere with a core density ρ₀∼ 0.17±0.03M_☉/pc3 and a core radius r_c∼ 0.9±0.1 kpc.