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