Inadequate turbulent support in low-metallicity molecular clouds
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| Main Authors: | , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Lin, Lingrui Zhang, Zhi-Yu Wang, Junzhi Papadopoulos, Padelis P. Shi, Yong Gong, Yan Sun, Yan Sun, Yichen Bisbas, Thomas G. Romano, Donatella Li, Di Liu, Hauyu Baobab Qiu, Keping Liu, Lijie Luo, Gan Tsai, Chao-Wei Wu, Jingwen Feng, Siyi Zhang, Bo |
| author_facet | Lin, Lingrui Zhang, Zhi-Yu Wang, Junzhi Papadopoulos, Padelis P. Shi, Yong Gong, Yan Sun, Yan Sun, Yichen Bisbas, Thomas G. Romano, Donatella Li, Di Liu, Hauyu Baobab Qiu, Keping Liu, Lijie Luo, Gan Tsai, Chao-Wei Wu, Jingwen Feng, Siyi Zhang, Bo |
| contents | 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 ($E_{\rm k}$) counterbalances their self-gravitational energy ($E_{\rm g}$), setting their virial parameter $α_{\rm vir}=2E_{\rm k}/|E_{\rm g}|\approx1$. However, past studies either have been biased by the use of optically-thick lines or have been limited within the solar neighborhood and the inner Galaxy (Galactocentric radius $R_{\rm gc}<R_{\rm gc,\odot} \approx 8$ kpc). Here we present sensitive mapping observations of optically thin $^{13}$CO lines towards molecular clouds in the low-metallicity Galactic outer disk ($R_{\rm gc}\sim9-24$ kpc). By combining archival data from the inner Galaxy and four nearby metal-poor dwarf galaxies, we reveal a systematic trend of $α_{\rm vir}$, 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2501_07636 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Inadequate turbulent support in low-metallicity molecular clouds Lin, Lingrui Zhang, Zhi-Yu Wang, Junzhi Papadopoulos, Padelis P. Shi, Yong Gong, Yan Sun, Yan Sun, Yichen Bisbas, Thomas G. Romano, Donatella Li, Di Liu, Hauyu Baobab Qiu, Keping Liu, Lijie Luo, Gan Tsai, Chao-Wei Wu, Jingwen Feng, Siyi Zhang, Bo Astrophysics of Galaxies 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 ($E_{\rm k}$) counterbalances their self-gravitational energy ($E_{\rm g}$), setting their virial parameter $α_{\rm vir}=2E_{\rm k}/|E_{\rm g}|\approx1$. However, past studies either have been biased by the use of optically-thick lines or have been limited within the solar neighborhood and the inner Galaxy (Galactocentric radius $R_{\rm gc}<R_{\rm gc,\odot} \approx 8$ kpc). Here we present sensitive mapping observations of optically thin $^{13}$CO lines towards molecular clouds in the low-metallicity Galactic outer disk ($R_{\rm gc}\sim9-24$ kpc). By combining archival data from the inner Galaxy and four nearby metal-poor dwarf galaxies, we reveal a systematic trend of $α_{\rm vir}$, 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. |
| title | Inadequate turbulent support in low-metallicity molecular clouds |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2501.07636 |