The Impact of Cosmic Rays on Thermal Instability in the Circumgalactic Medium

Large reservoirs of cold (∼104 K) gas exist out to and beyond the virial radius in the circumgalactic medium (CGM) of all types of galaxies. Photoionization modeling suggests that cold CGM gas has significantly lower densities than expected by theoretical predictions based on thermal pressure equili...

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2020-11, Vol.903 (2), p.77
Main Authors: Butsky, Iryna S., Fielding, Drummond B., Hayward, Christopher C., Hummels, Cameron B., Quinn, Thomas R., Werk, Jessica K.
Format: Article
Language:English
Subjects:
Astronomical models
Astrophysical fluid dynamics
Astrophysics
Circumgalactic medium
Cloud sizes
Cold
Cold gas
Computational fluid dynamics
Constraint modelling
Cosmic rays
Deposition
Diffusion rate
Fluid flow
Galaxies
Galaxy accretion
Galaxy evolution
Instability
Magnetohydrodynamic simulation
Magnetohydrodynamical simulations
Photoionization
Physicists
Simulation
Thermal instability
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Large reservoirs of cold (∼104 K) gas exist out to and beyond the virial radius in the circumgalactic medium (CGM) of all types of galaxies. Photoionization modeling suggests that cold CGM gas has significantly lower densities than expected by theoretical predictions based on thermal pressure equilibrium with hot CGM gas. In this work, we investigate the impact of cosmic-ray physics on the formation of cold gas via thermal instability. We use idealized three-dimensional magnetohydrodynamic simulations to follow the evolution of thermally unstable gas in a gravitationally stratified medium. We find that cosmic-ray pressure lowers the density and increases the size of cold gas clouds formed through thermal instability. We develop a simple model for how the cold cloud sizes and the relative densities of cold and hot gas depend on cosmic-ray pressure. Cosmic-ray pressure can help counteract gravity to keep cold gas in the CGM for longer, thereby increasing the predicted cold mass fraction and decreasing the predicted cold gas inflow rates. Efficient cosmic-ray transport, by streaming or diffusion, redistributes cosmic-ray pressure from the cold gas to the background medium, resulting in cold gas properties that are in between those predicted by simulations with inefficient transport and simulations without cosmic rays. We show that cosmic rays can significantly reduce galactic accretion rates and resolve the tension between theoretical models and observational constraints on the properties of cold CGM gas.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/abbad2