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<p>The dynamic properties of molecular clouds are set by the interplay of their self-gravity, turbulence, external pressure and magnetic fields. Extended surveys of Galactic molecular clouds typically find that their kinetic energy (<i>E</i><sub>k</sub>) counterbalances their self-gravitational energy (<i>E</i><sub>g</sub>), setting their virial parameter <i>α</i><sub>vir</sub> = 2<i>E</i><sub>k</sub>/∣<i>E</i><sub>g</sub>∣ ≈ 1. However, past studies either have been biased by the use of optically thick lines or have been limited within the solar neighbourhood and the inner Galaxy (Galactocentric radius <i>R</i><sub>gc</sub> &lt; <i>R</i><sub>gc,⊙</sub> ≈ 8 kpc). Here we present sensitive mapping observations of optically thin <sup>13</sup>CO lines towards molecular clouds in the low-metallicity Galactic outer disk (<i>R</i><sub>gc</sub> ~ 9–24 kpc). By combining archival data from the inner Galaxy and four nearby metal-poor dwarf galaxies, we reveal a systematic trend of <i>α</i><sub>vir</sub>, which declines from supervirial dynamic states in metal-rich clouds to extremely subvirial dynamic states in metal-poor clouds. In these metal-poor environments, turbulence alone is insufficient to counterbalance the self-gravity of a cloud. A cloud-volumetric magnetic field may replace turbulence as the dominant cloud-supporting mechanism in low-metallicity conditions, for example, the outermost galactic disks, dwarf galaxies and galaxies in the early Universe, which would then inevitably impact the initial conditions for star formation in such environments.</p>

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Inadequate turbulent support in low-metallicity molecular clouds

  • 期刊论文

  • 发表日期：

    2025年1月10日

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  • Lingrui Lin,
  • Zhi-Yu Zhang,
  • Junzhi Wang,
  • Padelis P. Papadopoulos,
  • Yong Shi,
  • Yan Gong,
  • Yan Sun,
  • Yichen Sun,
  • Thomas G. Bisbas,
  • Donatella Romano,
  • Di Li,
  • Hauyu Baobab Liu,
  • Keping Qiu,
  • Lijie Liu,
  • Gan Luo,
  • Chao-Wei Tsai,
  • Jingwen Wu,
  • Siyi Feng,
  • Bo Zhang

摘要

The dynamic properties of molecular clouds are set by the interplay of their self-gravity, turbulence, external pressure and magnetic fields. Extended surveys of Galactic molecular clouds typically find that their kinetic energy (Ek) counterbalances their self-gravitational energy (Eg), setting their virial parameter αvir = 2Ek/∣Eg∣ ≈ 1. However, past studies either have been biased by the use of optically thick lines or have been limited within the solar neighbourhood and the inner Galaxy (Galactocentric radius Rgc < Rgc,⊙ ≈ 8 kpc). Here we present sensitive mapping observations of optically thin 13CO lines towards molecular clouds in the low-metallicity Galactic outer disk (Rgc ~ 9–24 kpc). By combining archival data from the inner Galaxy and four nearby metal-poor dwarf galaxies, we reveal a systematic trend of αvir, which declines from supervirial dynamic states in metal-rich clouds to extremely subvirial dynamic states in metal-poor clouds. In these metal-poor environments, turbulence alone is insufficient to counterbalance the self-gravity of a cloud. A cloud-volumetric magnetic field may replace turbulence as the dominant cloud-supporting mechanism in low-metallicity conditions, for example, the outermost galactic disks, dwarf galaxies and galaxies in the early Universe, which would then inevitably impact the initial conditions for star formation in such environments.