Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 1S022

Dynamical State of The Serpens South Infrared Dark Cloud: From Pre-Protocluster Phase to Protocluster Phase

Nakamura, Fumitaka (National Astronomical Observatory of Japan)
Tomohiro, Tanaka (Osaka Prefecture University)
Yuya, Awazu (Okasa Prefecture University)
Yoshito, Shimajiri (CEA/Saclay)
Koji, Sugitani (Nagoya City University)
Ryohei, Kawabe (National Astronomical Observatory of Japan)
Hiroshige, Yoshida (CSO)
Toshikazu, Onishi (Osaka Prefecture University)
Aya E., Higuchi (Join ALMA Observatory)

Abstract:
We present the results of N2H+ (J=1-0) observations toward Serpens South, the nearest cluster-forming, infrared dark cloud. The physical quantities are derived by applying the N2H+ hyperfine fitting. The Herschel and 1.1-mm continuum maps show that a few pc-scale filament fragments into three clumps with radii of 0.1-0.2 pc and masses of 40-230Msolar. 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 N2H+ 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 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 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 contradict to the accretion-driven turbulence scenario, for which the turbulence in the clumps is maintained by the accretion flow.

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