Effects of cloud geometry and metallicity on shattering and coagulation of cold gas, and implications for cold streams penetrating virial shocks

Zhiyuan Yao*, Nir Mandelker*, S. Peng Oh, Han Aung, Avishai Dekel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

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. We study the 'shattering' of large, thermally unstable clouds into tiny cloudlets of size ℓ shatter ∼ min(cstcool) us using idealized numerical simulations. We expand upon previous works by exploring the effects of cloud geometry (spheres, streams, and sheets), metallicity, and an ionizing ultraviolet background. We find that 'shattering' is mainly triggered by clouds losing sonic contact and rapidly imploding, leading to a reflected shock that causes the cloud to re-expand and induces Richtmyer-Meshkov instabilities at its interface. The fragmented cloudlets experience a drag force from the surrounding hot gas, leading to recoagulation into larger clouds. We distinguish between 'fast' and 'slow' coagulation regimes. Sheets are always in the 'fast' coagulation regime, while streams and spheres transition to 'slow' coagulation above a critical overdensity, which is smallest for spheres. Surprisingly, ℓ shatter 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 cold streams feeding massive (Mv> ∼ 1012 M ⊙) galaxies at z >∼ 2 from the cosmic web, finding that streams likely shatter upon entering the hot CGM through the virial shock. This could explain the large clumping factors and covering fractions of cold gas around such galaxies, and may be related to galaxy quenching by preventing cold streams from reaching the central galaxy.

Original languageEnglish
Pages (from-to)3053-3089
Number of pages37
JournalMonthly Notices of the Royal Astronomical Society
Volume536
Issue number3
DOIs
StatePublished - 1 Jan 2025

Bibliographical note

Publisher Copyright:
© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.

Keywords

  • galaxies: evolution
  • galaxies: haloes
  • hydrodynamics
  • instabilities
  • intergalactic medium

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