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

Abstract

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. 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. The wide 2x2 arcminutes field and the high spectral resolution of the HARP instrument on JCMT provides information on the spatial structure and kinematics of the cloud. For species where multiple transitions are available, we estimate excitation temperatures and column densities. 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. 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 high density tracers (e.g. HCN, HNC, CS, HCO+) and tracers of UV-irradiation (e.g. CN and C2H). Large variations are seen between the sub-regions 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 South-west 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 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.

Proposed for acceptance in A&A, abstract abridged

References in corpus (11)

• The distance to the Orion Nebula
• SiO line emission from C-type shock waves : interstellar jets and outflows
• Low sulfur depletion in the Horsehead PDR
• Warm SiO gas in molecular bullets associated with protostellar outflows
• Sulphur-bearing species in the star forming region L1689N
• The penetration of FUV radiation into molecular clouds
• HCO mapping of the Horsehead : Tracing the illuminated dense molecular cloud surfaces
• Formaldehyde Densitometry of Starburst Galaxies
• Detection of extragalactic H3O+
• The JCMT Spectral Legacy Survey
• The Discovery of a Very Massive Star in W49

Cited by in corpus (12)

• ALMA HCN and HCO+ J=3-2 observations of optical Seyfert and luminous infrared galaxies -- Confirmation of elevated HCN-to-HCO+ flux ratios in AGNs --
• LEGO II: A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way Disc
• Molecular-Cloud-Scale Chemical Composition II: Mapping Spectral Line Survey toward W3(OH) in the 3 mm Band
• Herschel / HIFI spectral line survey of the Orion Bar - Temperature and density differentiation near the PDR surface
• Diverse nuclear star-forming activities in the heart of NGC 253 resolved with ten-pc scale ALMA images
• Sulphur-rich cold gas around the hot core precursor G328.2551-0.5321. An APEX unbiased spectral survey of the 2 mm, 1.2 mm, and 0.8 mm atmospheric windows
• ALMA Observations of the massive molecular outflow G331.512-0.103 II: physical properties, kinematics, and geometry modeling
• Identification of molecular clouds in emission maps: a comparison between methods in the \ce{^{13}CO}/\ce{C^{18}O} ($J=3-2$) Heterodyne Inner Milky Way Plane Survey
• Evidence for dense gas heated by the explosion in Orion KL
• An imaging line survey of OMC-1 to OMC-3
• A spectral survey of CH3CCH in the Hot Molecular Core G331.512-0.103
• Observations and Analysis of Absorption Lines including J = K Rotational Levels of CH3CN: The Envelope of Sagittarius B2(M)