The Panchromatic Circumgalactic Medium

TL;DR

This paper reviews the complex, multi-phase circumgalactic medium (CGM) surrounding galaxies, highlighting recent observational progress and outlining key questions about its composition, dynamics, and relationship with host galaxies and the intergalactic environment.

Contribution

It provides a comprehensive overview of the current understanding and challenges in studying the CGM, emphasizing the need for multi-wavelength observations to address fundamental questions.

Findings

Progress in observing cosmic-ray and magnetic fields in the CGM

Identification of the multi-phase nature of the CGM

Open questions about the CGM's energy, mass, and metal distribution

Abstract

Galaxies are surrounded by extended atmospheres, which are often called the circumgalactic medium (CGM) and are the least understood part of galactic ecosystems. The CGM serves as a reservoir of both diffuse, metal-poor gas accreted from the intergalactic medium, and metal-rich gas that is either ejected from galaxies by energetic feedback or stripped from infalling satellites. As such, the CGM is empirically multi-phased and complex in dynamics. Significant progress has been made in the past decade or so in observing the cosmic-ray/B-field, as well as various phases of the CGM. But basic questions remain to be answered. First, what are the energy, mass, and metal contents of the CGM? More specifically, how are they spatially distributed and partitioned in the different components? Moreover, how are they linked to properties of host galaxies and their global clustering and intergalactic medium environments? Lastly, what are the origin, state, and life-cycle of the CGM? This question explores the dynamics of the CGM. Here we illustrate how these questions may be addressed with multi-wavelength observations of the CGM.