Effects of Cloud Geometry and Metallicity on Shattering and Coagulation of Cold Gas, and Implications for Cold Streams Penetrating Virial Shocks
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2024
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| author | Yao, Zhiyuan Mandelker, Nir Oh, S. Peng Aung, Han Dekel, Avishai |
| author_facet | Yao, Zhiyuan Mandelker, Nir Oh, S. Peng Aung, Han Dekel, Avishai |
| contents | Theory and observations reveal that the circumgalactic medium (CGM) and the cosmic web at high redshifts are multiphase, with small clouds of cold gas embedded in a hot, diffuse medium. A proposed mechanism is `shattering' of large, thermally unstable clouds into tiny cloudlets of size lshatter~min(cs*tcool). We study these processes using idealized numerical simulations of thermally unstable gas clouds. We expand upon previous works by exploring the effects of cloud geometry (spheres, streams, and sheets), metallicity, and the inclusion of an ionizing UV background. We find that `shattering' is triggered by clouds losing sonic contact and rapidly imploding, leading to a reflected shock which causes the cloud to re-expand and induces Richtmyer-Meshkov instabilities at its interface. After fragmentation the cloudlets experience a drag force from the surrounding hot gas, leading to recoagulation into larger clouds. We distinguish between `fast' and `slow' coagulation regimes, showing that sheets are always in the `fast' coagulation regime while streams and spheres have a maximum overdensity for rapid coagulation. The critical overdensity for spheres is smaller than for streams, such that the coagulation efficiency increases from spheres to streams to sheets. Surprisingly, lshatter does not appear to be a characteristic clump size even if it is well resolved. Rather, fragmentation continues until the grid scale with a mass distribution of N(>m)~m^{-1}. We apply our results to the case of cold streams feeding massive (Mv>10^{12}Msun) high-z (z>2) galaxies from the cosmic web, finding that streams are likely to shatter upon entering the CGM through the virial shock. This could explain the large clumping factors and covering fractions of cold gas in the CGM around such galaxies, and may be related to galaxy quenching by preventing cold streams from reaching the central galaxy. [abridged] |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2410_12914 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Effects of Cloud Geometry and Metallicity on Shattering and Coagulation of Cold Gas, and Implications for Cold Streams Penetrating Virial Shocks Yao, Zhiyuan Mandelker, Nir Oh, S. Peng Aung, Han Dekel, Avishai Astrophysics of Galaxies Theory and observations reveal that the circumgalactic medium (CGM) and the cosmic web at high redshifts are multiphase, with small clouds of cold gas embedded in a hot, diffuse medium. A proposed mechanism is `shattering' of large, thermally unstable clouds into tiny cloudlets of size lshatter~min(cs*tcool). We study these processes using idealized numerical simulations of thermally unstable gas clouds. We expand upon previous works by exploring the effects of cloud geometry (spheres, streams, and sheets), metallicity, and the inclusion of an ionizing UV background. We find that `shattering' is triggered by clouds losing sonic contact and rapidly imploding, leading to a reflected shock which causes the cloud to re-expand and induces Richtmyer-Meshkov instabilities at its interface. After fragmentation the cloudlets experience a drag force from the surrounding hot gas, leading to recoagulation into larger clouds. We distinguish between `fast' and `slow' coagulation regimes, showing that sheets are always in the `fast' coagulation regime while streams and spheres have a maximum overdensity for rapid coagulation. The critical overdensity for spheres is smaller than for streams, such that the coagulation efficiency increases from spheres to streams to sheets. Surprisingly, lshatter does not appear to be a characteristic clump size even if it is well resolved. Rather, fragmentation continues until the grid scale with a mass distribution of N(>m)~m^{-1}. We apply our results to the case of cold streams feeding massive (Mv>10^{12}Msun) high-z (z>2) galaxies from the cosmic web, finding that streams are likely to shatter upon entering the CGM through the virial shock. This could explain the large clumping factors and covering fractions of cold gas in the CGM around such galaxies, and may be related to galaxy quenching by preventing cold streams from reaching the central galaxy. [abridged] |
| title | Effects of Cloud Geometry and Metallicity on Shattering and Coagulation of Cold Gas, and Implications for Cold Streams Penetrating Virial Shocks |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2410.12914 |