ROTATIONAL DYNAMICS AND STAR FORMATION IN THE NEARBY DWARF GALAXY NGC 5238

Abstract

We present new H  i spectral-line images of the nearby low-mass galaxy NGC 5238, acquired with the Karl G. Jansky Very Large Array. Located at a distance of 4.51 ± 0.04 Mpc, NGC 5238 is an actively star-forming galaxy with widespread H α and ultraviolet (UV) continuum emission. The source is included in many ongoing and recent nearby galaxy surveys, but until this work the spatially resolved qualities of its neutral interstellar medium have remained unstudied. Our H  i images resolve the disk on physical scales of ∼400 pc, allowing us to undertake a detailed comparative study of the gaseous and stellar components. The H  i disk is asymmetric in the outer regions, and the areas of high H  i mass surface density display a crescent-shaped morphology that is slightly offset from the center of the stellar populations. The H  i column density exceeds 10 21 cm −2 in much of the disk. We quantify the degree of co-spatiality of dense H  i gas and sites of ongoing star formation as traced by far-UV and H α emission. The neutral gas kinematics are complex; using a spatially resolved position–velocity analysis, we infer a rotational velocity of 31 ± 5 km s −1 . We place NGC 5238 on the baryonic Tully–Fisher relation and contextualize the system among other low-mass galaxies.