Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages
The formation of molecular clouds out of H i gas is the first step toward star formation. Its metallicity dependence plays a key role in determining star formation throughout cosmic history. Previous theoretical studies with detailed chemical networks calculate thermal equilibrium states and/or ther...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ace34e |
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| author | Masato I. N. Kobayashi Kazunari Iwasaki Kengo Tomida Tsuyoshi Inoue Kazuyuki Omukai Kazuki Tokuda |
| author_facet | Masato I. N. Kobayashi Kazunari Iwasaki Kengo Tomida Tsuyoshi Inoue Kazuyuki Omukai Kazuki Tokuda |
| author_sort | Masato I. N. Kobayashi |
| collection | DOAJ |
| description | The formation of molecular clouds out of H i gas is the first step toward star formation. Its metallicity dependence plays a key role in determining star formation throughout cosmic history. Previous theoretical studies with detailed chemical networks calculate thermal equilibrium states and/or thermal evolution under one-zone collapsing background. The molecular cloud formation in reality, however, involves supersonic flows, and thus resolving the cloud internal turbulence/density structure in three dimensions is still essential. We here perform magnetohydrodynamics simulations of 20 km s ^−1 converging flows of warm neutral medium (WNM) with 1 μ G mean magnetic field in the metallicity range from the solar (1.0 Z _⊙ ) to 0.2 Z _⊙ environment. The cold neutral medium (CNM) clumps form faster with higher metallicity due to more efficient cooling. Meanwhile, their mass functions commonly follow ${dn}/{dm}\propto {m}^{-1.7}$ at three cooling times regardless of the metallicity. Their total turbulence power also commonly shows the Kolmogorov spectrum with its 80% in the solenoidal mode, while the CNM volume alone indicates the transition toward Larson’s law. These similarities measured at the same time in units of the cooling time suggest that the molecular cloud formation directly from the WNM alone requires a longer physical time in a lower-metallicity environment in the 1.0–0.2 Z _⊙ range. To explain the rapid formation of molecular clouds and subsequent massive star formation possibly within ≲10 Myr as observed in the Large/Small Magellanic Clouds, the H i gas already contains CNM volume instead of pure WNM. |
| first_indexed | 2024-03-12T02:57:25Z |
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| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T02:57:25Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-be3405fe45c849c08cd565c50ce002172023-09-03T15:13:20ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0195413810.3847/1538-4357/ace34eMetallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary StagesMasato I. N. Kobayashi0https://orcid.org/0000-0003-3990-1204Kazunari Iwasaki1https://orcid.org/0000-0002-2707-7548Kengo Tomida2https://orcid.org/0000-0001-8105-8113Tsuyoshi Inoue3https://orcid.org/0000-0002-7935-8771Kazuyuki Omukai4https://orcid.org/0000-0001-5922-180XKazuki Tokuda5https://orcid.org/0000-0002-2062-1600Division of Science, National Astronomical Observatory of Japan , Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan ; masato.kobayashi@nagoya-u.jp, kobayashi@ph1.uni-koeln.de; I. Physikalisches Institut, Universität zu Köln , Zülpicher Str 77, D-50937 Köln, GermanyCenter for Computational Astrophysics , National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, JapanAstronomical Institute, Graduate School of Science, Tohoku University , Aoba, Sendai, Miyagi 980-8578, JapanDepartment of Physics, Konan University , Okamoto 8-9-1, Kobe, JapanAstronomical Institute, Graduate School of Science, Tohoku University , Aoba, Sendai, Miyagi 980-8578, JapanDepartment of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan; ALMA Project, National Astronomical Observatory of Japan , Mitaka, Tokyo 181-8588, Japan; Department of Physics, Graduate School of Science, Osaka Metropolitan University , 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, JapanThe formation of molecular clouds out of H i gas is the first step toward star formation. Its metallicity dependence plays a key role in determining star formation throughout cosmic history. Previous theoretical studies with detailed chemical networks calculate thermal equilibrium states and/or thermal evolution under one-zone collapsing background. The molecular cloud formation in reality, however, involves supersonic flows, and thus resolving the cloud internal turbulence/density structure in three dimensions is still essential. We here perform magnetohydrodynamics simulations of 20 km s ^−1 converging flows of warm neutral medium (WNM) with 1 μ G mean magnetic field in the metallicity range from the solar (1.0 Z _⊙ ) to 0.2 Z _⊙ environment. The cold neutral medium (CNM) clumps form faster with higher metallicity due to more efficient cooling. Meanwhile, their mass functions commonly follow ${dn}/{dm}\propto {m}^{-1.7}$ at three cooling times regardless of the metallicity. Their total turbulence power also commonly shows the Kolmogorov spectrum with its 80% in the solenoidal mode, while the CNM volume alone indicates the transition toward Larson’s law. These similarities measured at the same time in units of the cooling time suggest that the molecular cloud formation directly from the WNM alone requires a longer physical time in a lower-metallicity environment in the 1.0–0.2 Z _⊙ range. To explain the rapid formation of molecular clouds and subsequent massive star formation possibly within ≲10 Myr as observed in the Large/Small Magellanic Clouds, the H i gas already contains CNM volume instead of pure WNM.https://doi.org/10.3847/1538-4357/ace34eInterstellar mediumWarm neutral mediumCold neutral mediumInterstellar dynamics |
| spellingShingle | Masato I. N. Kobayashi Kazunari Iwasaki Kengo Tomida Tsuyoshi Inoue Kazuyuki Omukai Kazuki Tokuda Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages The Astrophysical Journal Interstellar medium Warm neutral medium Cold neutral medium Interstellar dynamics |
| title | Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages |
| title_full | Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages |
| title_fullStr | Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages |
| title_full_unstemmed | Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages |
| title_short | Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages |
| title_sort | metallicity dependence of molecular cloud hierarchical structure at early evolutionary stages |
| topic | Interstellar medium Warm neutral medium Cold neutral medium Interstellar dynamics |
| url | https://doi.org/10.3847/1538-4357/ace34e |
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