W49A JCMT Spectral Legacy Survey spectroscopy

The chemical composition suggests the importance of shock, photon-dominated region (PDR), and hot core chemistry. Many molecular lines show a significant spatial extent across the maps including CO and its isotopologues, high density tracers (e.g., HCN, HNC, CS, HCO^+^), and tracers of UV irradiation (e.g., CN and C_2_H). The spatially extended species reveal a complex velocity-structure of W49A with possible infall and outflow motions.

Large variations are seen between the subregions with mostly blue-shifted emission toward the eastern tail, mostly red-shifted emission toward the northern clump, and emission peaking around the expected source velocity toward the southwest clump. A comparison of column density ratios of characteristic species observed toward W49A to Galactic PDRs suggests that while the chemistry toward the W49A center is driven by a combination of UV irradiation and shocks, UV irradiation dominates for the northern clump, eastern tail, and southwest clump regions.

A comparison to a starburst galaxy and an active galactic nucleus suggests similar C_2_H, CN, and H_2_CO abundances (with respect to the dense gas tracer ^34^CS) between the ~0.8pc scale probed for W49A and the >1kpc regions in external galaxies with global star formation.