Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 492, Issue 2, Pages 1841-1854Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stz3567
Keywords
ISM: clouds; ISM: structure; galaxies: evolution; galaxies: haloes; galaxies: kinematics and dynamics
Categories
Funding
- Alfred P. Sloan Research Fellowship
- NSF [1715847, 1455342, XSEDE TG-AST130039, PRAC NSF.1713353]
- NASA [NNX15AT06G, JPL 1589742, 17-ATP17-0214, HEC SMD-167592]
- Royal Society Te Aparangi through a Rutherford Discovery Fellowship [RDF-U001804]
- Marsden Fund [UOO1727]
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We explore the survival of cool clouds in multiphase circumgalactic media. We revisit the 'cloud-crushing problem' in a large survey of simulations including radiative cooling, self-shielding, self-gravity, magnetic fields, and anisotropic Braginskii conduction and viscosity (with saturation). We explore awide range of parameters including cloud size, velocity, ambient temperature and density, and a variety of magnetic field configurations and cloud turbulence. We find that realistic magnetic fields and turbulence have weaker effects on cloud survival; the most important physics is radiative cooling and conduction. Self-gravity and self-shielding are important for clouds that are initially Jeans-unstable, but largely irrelevant otherwise. Non-self-gravitating, realistically magnetized clouds separate into four regimes: (1) at low column densities, clouds evaporate rapidly via conduction; (2) a 'failed pressure confinement' regime, where the ambient hot gas cools too rapidly to provide pressure confinement for the cloud; (3) an 'infinitely long-lived' regime, in which the cloud lifetime becomes longer than the cooling time of gas swept up in the leading bow shock, so the cloud begins to accrete and grow; and (4) a 'classical cloud destruction' regime, where clouds are eventually destroyed by instabilities. In the final regime, the cloud lifetime can exceed the naive cloud-crushing time owing to conduction-induced compression. However, small and/or slow-moving clouds can also evaporate more rapidly than the cloud-crushing time. We develop simple analytic models that explain the simulated cloud destruction times in this regime.
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