SMA observations of C2H in High-Mass Star Forming Regions

Abstract

C${}_2$H is a representative hydrocarbon that is abundant and ubiquitous in the interstellar medium (ISM). To study its chemical properties, we present Submillimeter Array (SMA) observations of the C${}_2$H $N=3-2$ and HC${}_3$N $J=30-29$ transitions and the 1.1 mm continuum emission toward four OB cluster-forming regions, AFGL 490, ON 1, W33 Main, and G10.6-0.4, which cover a bolometric luminosity range of $\sim$10${}^3$--10${}^6$ $L_{\odot }$. We found that on large scales, the C${}_2$H emission traces the dense molecular envelope. However, for all observed sources, the peaks of C${}_2$H emission are offset by several times times 10${}^4$ AU from the peaks of 1.1 mm continuum emission, where the most luminous stars are located. By comparing the distribution and profiles of C${}_2$H hyperfine lines and the 1.1 mm continuum emission, we find that the C${}_2$H column density (and abundance) around the 1.1 mm continuum peaks is lower than those in the ambient gas envelope. Chemical models suggest that C${}_2$H might be transformed to other species owing to increased temperature and density; thus, its reduced abundance could be the signpost of the heated molecular gas in the $\sim$10${}^4$ AU vicinity around the embedded high-mass stars. Our results support such theoretical prediction for centrally embedded $\sim 10^3$--$10^6{L}_{\odot }$ OB star-forming cores, while future higher-resolution observations are required to examine the C${}_2$H transformation around the localized sites of high-mass star formation.

10 pages, 6 figures. ApJ accepted. Comments welcome

References in corpus (5)

• ALMA Multi-line Imaging of the Nearby Starburst Galaxy NGC 253
• Ethynyl (C2H) in massive star formation: Tracing the initial conditions?
• VLA observations of ammonia in high-mass star formation regions
• Star formation in a clustered environment around the UCHII region in IRAS 20293+3952
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Cited by in corpus (7)

• FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) : Molecular clouds toward W33 ; possible evidence for a cloud-cloud collision triggering O star formation
• The evolution of temperature and density structures of OB cluster-forming molecular clumps
• C2H N=1-0 and N2H+ J=1-0 observations of Planck Galactic cold clumps
• Carbon Chain Chemistry in Hot-Core Regions around Three Massive Young Stellar Objects Associated with 6.7 GHz Methanol Masers
• Uncovering distinct environments in an extended physical system around the W33 complex
• Carbon-chain molecule survey toward four low-mass molecular outflow sources
• Sub-arcsecond Imaging of the Complex Organic Chemistry in Massive Star-forming Region G10.6-0.4