Cluster formation in the W40 and Serpens South complex triggered by the expanding HII region

Abstract

We present results of the mapping observations covering a large area of 1 square degree around W40 and Serpens South carried out in the 12CO (J=1-0), 13CO (J=1-0), C18O (J=1-0), CCS (J_{N}=8_{7}-7_{6}), and N_2H+ (J=1-0) emission lines with the 45 m Nobeyama Radio Telescope. W40 is a blistered Hii region, and Serpens South is an infrared dark cloud accompanied by a young cluster. The relationship between these two regions which are separated by ~20' on the sky has not been clear so far. We found that the C18O emission is distributed smoothly throughout the W40 and Serpens South regions, and it seems that the two regions are physically connected. We divided the C18O emission into four groups in terms of the spatial distributions around the HII region which we call 5, 6, 7, and 8 km s^{-1} components according to their typical LSR velocities, and propose a three-dimensional model of the W40 and Serpens South complex. We found two elliptical structures in position-velocity diagrams, which can be explained as a part of two expanding shells. One of the shells is the small inner shell just around the HII region, and the other is the large outer shell corresponding to the boundary of the HII region. Dense gas associated with the young cluster of Serpens South is likely to be located at the surface of the outer shell, indicating that the natal clump of the young cluster is interacting with the outer shell being compressed by the expansion of the shell. We suggest that the expansion of the shell induced the formation of the young cluster.

18 figures, accepted for publication in PASJ (the special issue of the Nobeyama FOREST receiver, "Nobeyama 45m Telescope: Legacy Projects and Receiver FOREST")

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• Nobeyama 45-m mapping observations toward nearby molecular clouds, Orion A, Aquila Rift, and M17: Project overview
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• Large-scale molecular gas distribution in the M17 cloud complex: dense gas conditions of massive star formation?
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• Deep Near-Infrared Survey Toward the W40 and Serpens South Region in Aquila Rift: A Comprehensive Catalog of Young Stellar Objects
• The distance to the Serpens South Cluster from H2O masers
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• Cloud structures in M17 SWex : Possible cloud-cloud collision
• Spatial distributions and kinematics of shocked and ionized gas in M17
• ASASSN-14ho: Longest-period Dwarf Nova with Multiple Rebrightenings
• New Massive Contact Twin Binary in a Radio-quiet HII Region Associated with the M17 Complex
• Cluster Formation in GGD12-15: Infall Motion with Rotation of the Natal Clump
• Sub-kpc scale gas density histogram of the Galactic molecular gas: a new statistical method to characterise galactic-scale gas structures
• FIRESTORM I: Stellar Feedback and Gas Kinematics in the Evolved W40 Hub-Filament System
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