SWAN: NGC 253's Nucleated Star Bursting Environment

AbstractWe present the first results from SWAN: “Survey of Water and Ammonia in Nearby galaxies”. Nearby galaxies are conveniently located to probe molecular gas properties on scales of 10 to 200 pc, which are appropriate for the study of Giant Molecular Clouds (GMCs). The resolution of the Very Large Array in D and C configurations corresponds to a few 10s of parsecs in these galaxies. To advance studies of galaxy evolution it is paramount to understand how processes in the molecular Interstellar Medium(ISM) and star formation are linked on these scales. We have observed the metastable transitions of ammonia and the 22GHz water maser line in four nearby galaxies: NGC 253, IC 342, NGC 2146, and NGC 6946 using the VLA. These galaxies were chosen to span an order of magnitude in star formation rate, and a range of galactic ecosystems. We use the ammonia transitions to derive kinetic temperatures, which exposes the heating and cooling balance of the ISM. We then aim to relate these conditions to energetic feedback from star formation as indicated by water masers.Currently, our analysis is focused on NGC 253. NGC 253 is a barred spiral starburst galaxy with a nucleated star formation rate (SFR) of ≈ 3M⊙ per year. We use a distance of 3.9Mpc for analysis. We have observed ammonia transitions (1,1) to (5,5) and the 22GHz water maser line with a resolution of ≈63pc. We have identified nine regions across the nucleated starburst for study. The ammonia (3,3) line appears to be masing in the centermost 200pc. We have identified two regions of water maser emission. The first region is a minor axis extension, about the center of the galaxy, and is very close to the outflow. By means of these measurements, we gain an understanding of the molecular ISM associated with the nucleated starburst environment in NGC 253.