Three-dimensional modeling of the HI kinematics of NGC 2915

The nearby blue compact dwarf, NGC 2915, has its stellar disc embedded in a large, extended (~ 22 B-band scale-lengths) HI disc. New high-resolution HI synthesis observations of NGC 2915 have been obtained with the Australia Telescope Compact Array. These observations provide evidence of extremely complex HI kinematics within the immediate vicinity of the galaxy's star-forming core. We identify and quantify double-peaked HI line profiles near the centre of the galaxy and show that the HI energetics can be accounted for by the mechanical energy output of the central high-mass stellar population within time-scales of 10^6-10^7 yr. Full three-dimensional models of the HI data cube are generated and compared to the observations to test various physical scenarios associated with the high-mass star-forming core of NGC 2915. Purely circular HI kinematics are ruled out together with the possibility of a high-velocity-dispersion inter-stellar medium at inner radii. Radial velocities of ~ 30 km/s are required to describe the central-most HI kinematics of the system. Our results lend themselves to the simple physical scenario in which the young stellar core of the galaxy expels the gas outwards from the centre of the disc, thereby creating a central HI under-density. These kinematics should be thought of as being linked to a central HI outflow rather than a large-scale galactic blow-out or wind.