ALMA MULTI-LINE IMAGING OF THE NEARBY STARBURST NGC 253

We present spatially resolved (similar to 50 pc) imaging of molecular gas species in the central kiloparsec of the nearby starburst galaxy NGC 253, based on observations taken with the Atacama Large Millimeter/submillimeter Array. A total of 50 molecular lines are detected over a 13 GHz bandwidth imaged in the 3 mm band. Unambiguous identifications are assigned for 27 lines. Based on the measured high CO/(CO)-O-17 isotopic line ratio (similar to 350), we show that (CO)-C-12(1-0) has moderate optical depths. A comparison of the HCN and HCO+ with their C-13-substituted isotopologues shows that the HCN(1-0) and HCO+ (1-0) lines have optical depths at least comparable to CO(1-0). (HCN)-C-13/(HCO+)-C-13 (and (HCN)-C-13/(HNC)-C-13) line ratios provide tighter constraints on dense gas properties in this starburst. SiO has elevated abundances across the nucleus. HNCO has the most distinctive morphology of all the bright lines, with its global luminosity dominated by the outer parts of the central region. The dramatic variation seen in the HNCO/SiO line ratio suggests that some of the chemical signatures of shocked gas are being erased in the presence of dominating central radiation fields (traced by C2H and CN). High density molecular gas tracers (including HCN, HCO+, and CN) are detected at the base of the molecular outflow. We also detect hydrogen beta recombination lines that, like their a counterparts, show compact, centrally peaked morphologies, distinct from the molecular gas tracers. Anumber of sulfur based species aremapped (CS, SO, NS, C2S, H2CS, and CH3SH) and have morphologies similar to SiO.