Three-dimensional modelling of the H I kinematics of NGC 2915

The nearby blue compact dwarf, NGC 2915, has its stellar disc embedded in a large, extended (∼22 B-band scalelengths) H I disc. New high-resolution H I synthesis observations of NGC 2915 have been obtained with the Australia Telescope Compact Array. These observations provide evidence of extremely complex H I kinematics within the immediate vicinity of the galaxy's star-forming core. We identify and quantify double-peaked H I line profiles near the centre of the galaxy and show that the H I energetics can be accounted for by the mechanical energy output of the central high-mass stellar population within time-scales of 10⁶-10⁷ yr. Full three-dimensional models of the H I 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 H I kinematics are ruled out together with the possibility of a high-velocity-dispersion interstellar medium at inner radii. Radial velocities of ∼30 km s^-1 are required to describe the central-most H I 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 H I underdensity. These kinematics should be thought of as being linked to a central H I outflow rather than a large-scale galactic blowout or wind.