The Complex Neutral Gas Dynamics of the Dwarf Starburst Galaxy NGC 625

Abstract

We present new multiconfiguration H i aperture synthesis imaging of the nearby dwarf starburst galaxy NGC 625 obtained with the Australia Telescope Compact Array. Total H i column density images show gas well aligned with the optical major axis and low column density H i extending to greater than 6 optical scale lengths. The H i velocity field, on the other hand, is highly disturbed, with neutral gas at nearly all detected velocities within the central region. After considering various interpretations, we find that a blowout scenario most accurately describes the data. Since at our resolution we do not detect any large evacuated holes in the H i disk, we interpret this blowout to be the result of the extended (both spatially and temporally) star formation event that NGC 625 has undergone in the last 100 Myr. This is one of the clearest examples of H i outflow detected in a dwarf galaxy. We find no obvious external trigger for this extended star formation event. We detect strong radio continuum emission from the largest H ii regions; comparing to our Hubble Space Telescope and ground-based H fluxes suggests either appreciable amounts of extinction toward the star formation regions or the contribution of nonthermal sources to the radio continuum luminosity.