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Title: FORMATION OF TURBULENT AND MAGNETIZED MOLECULAR CLOUDS VIA ACCRETION FLOWS OF H I CLOUDS

Abstract

Using three-dimensional magnetohydrodynamic simulations, including the effects of radiative cooling/heating, chemical reactions, and thermal conduction, we investigate the formation of molecular clouds in the multi-phase interstellar medium. As suggested by recent observations, we consider the formation of molecular clouds due to accretion of H I clouds. Our simulations show that the initial H I medium is piled up behind the shock waves induced by accretion flows. Since the initial medium is highly inhomogeneous as a consequence of thermal instability, a newly formed molecular cloud becomes very turbulent owing to the development of the Richtmyer-Meshkov instability. The kinetic energy of the turbulence dominates the thermal, magnetic, and gravitational energies throughout the entire 10 Myr evolution. However, the kinetic energy measured using CO-fraction-weighted densities is comparable to the other energies, once the CO molecules are sufficiently formed as a result of UV shielding. This suggests that the true kinetic energy of turbulence in molecular clouds as a whole can be much larger than the kinetic energy of turbulence estimated using line widths of molecular emission. We find that clumps in a molecular cloud show the following statistically homogeneous evolution: the typical plasma {beta} of the clumps is roughly constant ({beta}) {approx_equal} 0.4;more » the size-velocity dispersion relation is {Delta}v {approx_equal} 1.5 km s{sup -1} (l/1 pc){sup 0.5}, irrespective of the density; the clumps evolve toward magnetically supercritical, gravitationally unstable cores; and the clumps seem to evolve into cores that satisfy the condition for fragmentation into binaries. These statistical properties may represent the initial conditions of star formation.« less

Authors:
 [1];  [2]
  1. Department of Physics and Mathematics, Aoyama Gakuin University, Fuchinobe, Chuou-ku, Sagamihara 252-5258 (Japan)
  2. Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan)
Publication Date:
OSTI Identifier:
22086478
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 759; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; CARBON MONOXIDE; COMPUTERIZED SIMULATION; DISPERSION RELATIONS; GALAXIES; H1 REGIONS; KINETIC ENERGY; LINE WIDTHS; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; MOLECULES; PHOTON EMISSION; PLASMA; PLASMA INSTABILITY; RADIATIVE COOLING; SHOCK WAVES; STAR ACCRETION; THERMAL CONDUCTION; THREE-DIMENSIONAL CALCULATIONS

Citation Formats

Inoue, Tsuyoshi, and Inutsuka, Shu-ichiro, E-mail: inouety@phys.aoyama.ac.jp. FORMATION OF TURBULENT AND MAGNETIZED MOLECULAR CLOUDS VIA ACCRETION FLOWS OF H I CLOUDS. United States: N. p., 2012. Web. doi:10.1088/0004-637X/759/1/35.
Inoue, Tsuyoshi, & Inutsuka, Shu-ichiro, E-mail: inouety@phys.aoyama.ac.jp. FORMATION OF TURBULENT AND MAGNETIZED MOLECULAR CLOUDS VIA ACCRETION FLOWS OF H I CLOUDS. United States. doi:10.1088/0004-637X/759/1/35.
Inoue, Tsuyoshi, and Inutsuka, Shu-ichiro, E-mail: inouety@phys.aoyama.ac.jp. Thu . "FORMATION OF TURBULENT AND MAGNETIZED MOLECULAR CLOUDS VIA ACCRETION FLOWS OF H I CLOUDS". United States. doi:10.1088/0004-637X/759/1/35.
@article{osti_22086478,
title = {FORMATION OF TURBULENT AND MAGNETIZED MOLECULAR CLOUDS VIA ACCRETION FLOWS OF H I CLOUDS},
author = {Inoue, Tsuyoshi and Inutsuka, Shu-ichiro, E-mail: inouety@phys.aoyama.ac.jp},
abstractNote = {Using three-dimensional magnetohydrodynamic simulations, including the effects of radiative cooling/heating, chemical reactions, and thermal conduction, we investigate the formation of molecular clouds in the multi-phase interstellar medium. As suggested by recent observations, we consider the formation of molecular clouds due to accretion of H I clouds. Our simulations show that the initial H I medium is piled up behind the shock waves induced by accretion flows. Since the initial medium is highly inhomogeneous as a consequence of thermal instability, a newly formed molecular cloud becomes very turbulent owing to the development of the Richtmyer-Meshkov instability. The kinetic energy of the turbulence dominates the thermal, magnetic, and gravitational energies throughout the entire 10 Myr evolution. However, the kinetic energy measured using CO-fraction-weighted densities is comparable to the other energies, once the CO molecules are sufficiently formed as a result of UV shielding. This suggests that the true kinetic energy of turbulence in molecular clouds as a whole can be much larger than the kinetic energy of turbulence estimated using line widths of molecular emission. We find that clumps in a molecular cloud show the following statistically homogeneous evolution: the typical plasma {beta} of the clumps is roughly constant ({beta}) {approx_equal} 0.4; the size-velocity dispersion relation is {Delta}v {approx_equal} 1.5 km s{sup -1} (l/1 pc){sup 0.5}, irrespective of the density; the clumps evolve toward magnetically supercritical, gravitationally unstable cores; and the clumps seem to evolve into cores that satisfy the condition for fragmentation into binaries. These statistical properties may represent the initial conditions of star formation.},
doi = {10.1088/0004-637X/759/1/35},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 759,
place = {United States},
year = {2012},
month = {11}
}