Physical and chemical differentiation of the luminous star-forming region W49A

Nagy, Zsófia and van der Tak, F. F. S. and Fuller, G. A. and Plume, R. (2015) Physical and chemical differentiation of the luminous star-forming region W49A. ASTRONOMY & ASTROPHYSICS, 577. ISSN 0004-6361

Preview

Text 1502.03187.pdf Available under License Creative Commons Attribution. Download (2MB) | Preview

Abstract

Context. The massive and luminous star-forming region W49A is a well known Galactic candidate to probe the physical conditions and chemistry similar to those expected in external starburst galaxies. Aims. We aim to probe the physical and chemical structure of W49A on a spatial scale of ∼0.8 pc based on the JCMT Spectral Legacy Survey, which covers the frequency range between 330 and 373 GHz. Methods. The wide 2 × 2 arcminutes field and the high spectral resolution of the HARP instrument on JCMT provides information on the spatial structure and kinematics of the cloud traced by the observed molecular lines. For species where multiple transitions are available, we estimate excitation temperatures and column densities using a population diagram method that takes beam dilution and optical depth corrections into account. Results. We detected 255 transitions corresponding to 60 species in the 330-373 GHz range at the center position of W49A. Excitation conditions can be probed for 16 molecules, including the complex organic molecules CH3CCH, CH3CN, and CH3OH. The chemical composition suggests the importance of shock-, 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 C2H). The spatially extended species reveal a complex velocity-structure of W49A with possible infall and outflow motions. Large variations are seen between the sub-regions with mostly blue-shifted emission toward the Eastern tail, mostly redshifted emission toward the Northern clump, and emission peaking around the expected source velocity toward the South-west clump. Conclusions. 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 South-west clump regions. A comparison to a starburst galaxy and an AGN suggests similar C2H, CN, and H2CO abundances (with respect to the dense gas tracer 34CS) between the ∼0.8 pc scale probed for W49A and the >1 kpc regions in external galaxies with global star-formation.

Actions (login required)

Edit Item