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Filamentary Structure and Helical Magnetic Fields in the Environment of a Starless Dense Core

Falgarone, E. and Pety, J. and Phillips, T. G. (2001) Filamentary Structure and Helical Magnetic Fields in the Environment of a Starless Dense Core. Astrophysical Journal, 555 (1). pp. 178-190. ISSN 0004-637X. doi:10.1086/321483.

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The environment of L1512, a starless dense core, has been mapped at high angular resolution in the ^(12)CO (J = 2-1) line over more than 1 pc, with a few positions observed in the ^(12)CO (J = 3-2) and (J = 4-3) lines. The gas outside the dense core is structured in several filaments, roughly 1 pc long and ~0.1 pc thick, converging at the dense core position. Small longitudinal (~1 km s^(-1) pc^(-1)) but large transverse (up to 8 km s^(-1) pc^(-1)) velocity gradients are observed. Remarkably, the transverse gradients can be seen to change sign periodically, along at least one of the filaments. Thus, there are oscillations in the toroidal velocity within the filaments, which may be a signature of a magnetohydrodynamic instability developing in filaments permeated by a helical magnetic field. In the case of L1512, according to the analysis of Fiege & Pudritz, the growth rate of the instability is low, corresponding to a timescale of the order of 1 Myr. We deduce from the wavelength of the oscillations that the toroidal component of the magnetic field dominates the poloidal component. The toroidal component helps confine the filaments, which are not otherwise confined by self-gravity (m/m_(vir) ~ 0.2), by the pressure of the galactic H I layer, or by external turbulent pressure. We find that the velocity gradients in the vicinity of the dense core provide an estimate for an upper limit to the accretion rate onto the dense core of Ṁ = 4 × 10-6 M_☉ yr^(-1). For the gas characteristics in the filaments, we find that a broad range of density and temperature is allowed for the gas, from n_(H(_2)) = 2 × 10^3 cm^(-3) for the coldest case (T_k = 20 K) down to n_(H(_2)) = 180 cm^(-3) for the warmest (T_k = 250 K).

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Additional Information:© 2001. The American Astronomical Society. Received 2000 November 22; accepted 2001 February 22. One of us (E. F.) is grateful to R. Pudritz and J. Fiege for illuminating confrontations between observations and theory, which have inspired the tentative identification of the MHD instability in the filaments. E. F. also acknowledges the hospitality of the Institute for Theoretical Physics at the University of California, Santa Barbara (NSF grant PHY 99-07949) where this work has evolved. We thank M. Pérault for providing us with his LVG code. The Caltech Submillimeter Observatory is funded by NSF grant AST 99-80846.
Funding AgencyGrant Number
NSFPHY 99-07949
NSFAST 99-80846
Subject Keywords:ISM: clouds; ISM: magnetic fields; ISM: molecules
Issue or Number:1
Record Number:CaltechAUTHORS:20170408-172113269
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Official Citation:E. Falgarone et al 2001 ApJ 555 178
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76330
Deposited By: 1Science Import
Deposited On:13 Mar 2018 20:12
Last Modified:15 Nov 2021 16:59

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