Inflows and outflows in the dwarf starburst galaxy NGC 5253: High-resolution H i observations

Very Large Array and Parkes 64 m radiotelescope 21 cm observations of the starburst dwarf galaxy NGC 5253 reveal a multi-component non-axisymmetric H I distribution. The component associated with the stellar body shows evidence for a small amount of rotational support aligned with the major axis, in agreement with optically measured kinematics and consistent with the small galactic mass. Approximately 20-30% of the H I emission is associated with a second component, an H I "plume" extending along the optical minor axis to the southeast. We consider outflow, inflow, and tidal origins for this feature. Outflow appears improbable, inflow is a possibility, and tidal debris is most consistent with the observations. Thus, kinematics of the H I that include this feature are not indicative of the dynamical mass or the local velocity dispersion of the cold gas. These H I observations also reveal a filamentary third component that includes an 800 pc diameter H I shell or bubble to the west of the nucleus, coinciding with an Hα shell. The mass of H I in the shell may be as large as 4 × 10⁶ M _⊙. This large mass, coupled with the lack of expansion signatures in the neutral and ionized gas (v < 30 km s^-1), suggests that this feature may be an example of a starburst-blown bubble stalled by interaction with a massive neutral envelope. Many other H I kinematic features closely resemble those seen in Hα emission from the ionized gas, supporting the interpretation of neutral and ionized gas outflow at velocities of 30 km s^-1. Comparison between extinction estimates from the Balmer emission-line decrement and the H I column densities suggests a gas-to-dust ratio 2-3 times the Galactic value in this low-metallicity (Z = 1/4Z _⊙) galaxy.