The Circumgalactic Medium

TL;DR

The paper reviews recent advances in understanding the circumgalactic medium (CGM), emphasizing its complex, multiphase nature and critical role in galaxy evolution through observations and simulations.

Contribution

It provides a comprehensive overview of the current knowledge on the CGM's properties, dynamics, and its coevolution with galaxies, highlighting recent observational and simulation results.

Findings

CGM is a multiphase, dynamic medium with complex ionization states.

CGM acts as a key regulator of galactic gas supply and evolution.

Observations across redshifts confirm CGM's role in galaxy growth.

Abstract

The gas surrounding galaxies outside their disks or interstellar medium and inside their virial radii is known as the circumgalactic medium (CGM). In recent years this component of galaxies has assumed an important role in our understanding of galaxy evolution owing to rapid advances in observational access to this diffuse, nearly invisible material. Observations and simulations of this component of galaxies suggest that it is a multiphase medium characterized by rich dynamics and complex ionization states. The CGM is a source for a galaxy's star-forming fuel, the venue for galactic feedback and recycling, and perhaps the key regulator of the galactic gas supply. We review our evolving knowledge of the CGM with emphasis on its mass, dynamical state, and coevolution with galaxies. Observations from all redshifts and from across the electromagnetic spectrum indicate that CGM gas has a key role in galaxy evolution. We summarize the state of this field and pose unanswered questions for future research.