The Dynamical State of the Serpens South Filamentary Infrared Dark Cloud

Abstract

We present the results of N 2 H + (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 2 H + . The Herschel and 1.1-mm continuum maps show that a pc-scale filament fragments into three clumps with radii of 0.1 − 0.2 pc and masses of 40 − 230M ⊙ . 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 2 H + 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 globallyordered 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, it is 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.Recently, Nakamura et al. (2011) performed 12 CO (J = 3 − 2) mapping observations toward the Serpens South IRDC using the ASTE 10-m telescope and discovered that a number of powerfull outflows are blowing out of the central dense clump that is located near the southern edge of a

Confronting the Outflow-Regulated Cluster Formation Model With Observations

“…For Serpens South and ρ Oph, the virial parameters are found to be very small, α vir ∼ 0.2. For the Serpens South clump, Tanaka et al (2013) found that the infall motions are too slow compared to the free-fall velocity, implying that the magnetic support may play a role in the clump support (see also Sugitani et al 2011) and therefore we speculate that the "effective" virial parameter including the effect of magnetic support is close to unity. The ρ Oph clump also has a relatively small velocity dispersion, which is much smaller than the free-fall velocity.…”

“…The exceptions are Serpens South and ρ Oph, where the virial parameters are estimated to be as small as ∼ 0.2. In Serpens South, Sugitani et al (2011) revealed the existence of globally-ordered magnetic field that appears to be roughly perpendicular to the main filament, indicating that the magnetic support is important (see also Tanaka et al 2013). In contrast, for ρ Oph, no globally-ordered magnetic field has been observed (Tamura et al 2011).…”

Morphology and Kinematics of Filaments in the Serpens and Perseus Molecular Clouds

“…Both clouds have an average recessional velocity of 7.5 − 8 km/s. Dust temperatures in these filaments range from 12 K to 15 K (Roccatagliata et al 2015;Tanaka et al 2013). We use the Spitzer catalog of YSOs (Dunham et al 2015) and identified point sources in the Herschel 70 µm maps corresponding to the studied regions to compare their locations with respect to the structures identified by us.…”

A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from theHerschelGould Belt survey

“…Rescaled to the same distance, the virial mass for the entire Aquila Rift estimated by Dame & Thaddeus (1985) is ∼3.3 × 10 5 M , suggesting that the whole complex is close to virial balance on large scales. More recently, Tanaka et al (2013) obtained a virial parameter ∼0.08-0.24 for the Serpens South filament (again rescaled to a distance of 260 pc) on ∼0.5 pc scales (see also Kirk et al 2013a), and Maury et al (2011) derived a high star formation rate of ∼23 M Myr −1 pc −2 for the protocluster associated with the filament (of total mass ∼610 M , also using d = 260 pc). Altogether, these results suggest that the Aquila Rift complex is globally gravitationally bound on scales of ∼25 pc and includes a few highly unstable (sub-virial) clumps on the verge of forming rich star clusters on sub-parsec scales.…”