The Circumgalactic Medium

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.

46 pages, 11 figures. Authors' draft version; see http://www.annualreviews.org/doi/10.1146/annurev-astro-091916-055240 for a well-edited final version and fun supplementary figures

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• The REQUIEM Survey I: A Search for Extended Ly-Alpha Nebular Emission Around 31 z>5.7 Quasars
• A 100-kiloparsec wind feeding the circumgalactic medium of a massive compact galaxy
• Cooling flow solutions for the circumgalactic medium
• The extent of chemically enriched gas around star-forming dwarf galaxies
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• Anomalously low metallicity regions in MaNGA star-forming galaxies: Accretion Caught in Action?
• How Gas Accretion Feeds Galactic Disks
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• The MUSE Ultra Deep Field (MUDF). I. Discovery of a group of Ly$\alpha$ nebulae associated with a bright $z\approx 3.23$ quasar pair
• The abundance and physical properties of O VII and O VIII X-ray absorption systems in the EAGLE simulations
• The Relationship Between Galaxy ISM and Circumgalactic Gas Metallicities
• Galaxy wide radio induced feedback in a radio quiet quasar
• Circumgalactic Pressure Profiles Indicate Precipitation-Limited Atmospheres for $M_{\ast }\sim 10^9$$-$$10^{11.5}{M}_{\odot }$
• MusE GAs FLOw and Wind (MEGAFLOW) IV: A two sightline tomography of a galactic wind
• Chemical evolution of disc galaxies from cosmological simulations
• On the detectability of visible-wavelength line emission from the local circumgalactic and intergalactic medium
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• Simulating Gas Inflow at the Disk-Halo Interface
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• The Impact of Wind Scalings on Stellar Growth and the Baryon Cycle in Cosmological Simulations
• Cold neutral hydrogen gas in galaxies
• Charge exchange emission and cold clumps in multi-phase galactic outflows
• Nature and Origins of Rich Complexes of C IV Associated Absorption Lines
• Interpreting Observations of Absorption Lines in the Circumgalactic Medium with a Turbulent Medium
• Radio halos of star forming galaxies
• Probing gaseous halos of galaxies with radio jets
• Solar-Metallicity Gas in the Extended Halo of a Galaxy at $z\sim 0.12$