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The massive and luminous star-forming region W49A is a well known Galacticcandidate to probe the physical conditions and chemistry similar to thoseexpected in external starburst galaxies. We aim to probe the physical andchemical structure of W49A on a spatial scale of ~0.8 pc based on the JCMTSpectral Legacy Survey, which covers the frequency range between 330 and 373GHz. The wide 2x2 arcminutes field and the high spectral resolution of the HARPinstrument on JCMT provides information on the spatial structure and kinematicsof the cloud. For species where multiple transitions are available, we estimateexcitation temperatures and column densities. We detected 255 transitionscorresponding to 60 species in the 330-373 GHz range at the center position ofW49A. Excitation conditions can be probed for 16 molecules. The chemicalcomposition suggests the importance of shock-, PDR-, and hot core chemistry.Many molecular lines show a significant spatial extent across the mapsincluding high density tracers (e.g. HCN, HNC, CS, HCO+) and tracers ofUV-irradiation (e.g. CN and C2H). Large variations are seen between thesub-regions with mostly blue-shifted emission toward the Eastern tail, mostlyred-shifted emission toward the Northern clump, and emission peaking around theexpected source velocity toward the South-west clump. A comparison of columndensity ratios of characteristic species observed toward W49A to Galactic PDRssuggests that while the chemistry toward the W49A center is driven by acombination of UV-irradiation and shocks, UV-irradiation dominates for theNorthern Clump, Eastern tail, and South-west clump regions. A comparison to astarburst galaxy and an AGN suggests similar C2H, CN, and H2CO abundances (withrespect to the dense gas tracer 34CS) between the ~0.8 pc scale probed for W49Aand the >1 kpc regions in external galaxies with global star-formation.

Physical and chemical differentiation of the luminous star-forming region W49A - Results from the JCMT Spectral Legacy Survey