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The Dynamical State of the Serpens South Filamentary Infrared Dark Cloud

Tanaka, Tomohiro and Nakamura, Fumitaka and Awazu, Yuya and Shimajiri, Yoshito and Sugitani, Koji and Onishi, Toshikazu and Kawabe, Ryohei and Yoshida, Hiroshige and Higuchi, Aya E. (2013) The Dynamical State of the Serpens South Filamentary Infrared Dark Cloud. Astrophysical Journal, 778 (1). Art. No. 34. ISSN 0004-637X. doi:10.1088/0004-637X/778/1/34.

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We present the results of N_2H^+ (J = 1-0) observations toward Serpens South, the nearest cluster-forming, infrared dark cloud. The physical quantities are derived by fitting the hyperfine structure of N_2H^+. The Herschel and 1.1 mm continuum maps show that a parsec-scale filament fragments into three clumps with radii of 0.1-0.2 pc and masses of 40-230 M_☉. We find that the clumps contain smaller-scale (~0.04 pc) structures, i.e., dense cores. We identify 70 cores by applying CLUMPFIND to the N_2H^+ data cube. In the central cluster-forming clump, the excitation temperature and line-width tend to be large, presumably due to protostellar outflow feedback and stellar radiation. However, for all the clumps, the virial ratios are evaluated to be 0.1-0.3, indicating that the internal motions play only a minor role in the clump support. The clumps exhibit no free fall but exhibit low-velocity infall, and thus the clumps should be supported by additional forces. The most promising force is the globally ordered magnetic field observed toward this region. We propose that the Serpens South filament was close to magnetically critical and ambipolar diffusion triggered the cluster formation. We find that the northern clump, which shows no active star formation, has a mass and radius comparable to the central cluster-forming clump and is therefore a likely candidate of a pre-protocluster clump. The initial condition for cluster formation is likely to be a magnetically supported clump of cold, quiescent gas. This appears to contradict the accretion-driven turbulence scenario, for which the turbulence in the clumps is maintained by the accretion flow.

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Additional Information:© 2013 American Astronomical Society. Received 2013 April 15; accepted 2013 September 5; published 2013 October 31. This work is supported in part by a Grant-in-Aid for Scientific Research of Japan (20540228). We thank Thushara Pillai, Jens Kauffmann, Alvaro Hacar, Philippe André, and Huei-Ru Chen for valuable comments and suggestions. We are grateful to the staffs at the Nobeyama Radio Observatory (NRO) for both operating the 45 m and helping us with the data reduction. NRO is a branch of the National Astronomical Observatory, National Institutes of Natural Sciences, Japan. We also thank the staff at the Caltech Submillimeter Observatory for giving us an opportunity to use the telescope.
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Grant-in-Aid for Scientific Research of Japan20540228
Subject Keywords: ISM: clouds; ISM: kinematics and dynamics; ISM: structure; stars: formation
Issue or Number:1
Record Number:CaltechAUTHORS:20131223-135134517
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Official Citation: The Dynamical State of the Serpens South Filamentary Infrared Dark Cloud Tomohiro Tanaka et al. 2013 ApJ 778 34
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43149
Deposited By: Ruth Sustaita
Deposited On:23 Dec 2013 22:25
Last Modified:10 Nov 2021 16:33

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