Circumgalactic medium

The circumgalactic medium is diffuse gas surrounding a galaxy beyond its main stellar disk. It exchanges matter and energy with the galaxy and extends toward the surrounding intergalactic medium.

Cosmic accretion: The inflow of gas from the cosmic web into galaxies and their surroundings. Accreting gas replenishes the circumgalactic reservoir and can fuel star formation.
Dark matter halo: A gravitationally bound structure of dark matter surrounding a galaxy or galaxy group. The circumgalactic medium occupies the halo’s gaseous component.
Quasar absorption-line spectroscopy: The analysis of absorption imprinted on a quasar spectrum by intervening gas. Background quasars expose otherwise faint circumgalactic gas along narrow sightlines.
Galaxy formation: The formation and growth of galaxies through gravity, gas accretion, star formation, and feedback. The medium regulates the gas supply on which galaxy growth depends.
Missing baryons: Ordinary matter predicted by cosmology but not readily accounted for in observed stars and cold gas. How much of this matter resides in circumgalactic gas remains a central census question.
Galactic wind: A large-scale outflow of gas from a galaxy, driven by stellar activity or a central black hole. Winds carry energy and enriched material from galaxies into the surrounding gas.
Intergalactic medium: The diffuse matter occupying the space between galaxies. The circumgalactic medium grades into this broader reservoir beyond galaxy halos.
Lyman-alpha emission: Emission at the hydrogen Lyman-alpha wavelength, produced when hydrogen atoms change energy states. Its diffuse glow can reveal circumgalactic gas around distant galaxies.
Baryon cycle: The movement of ordinary matter between galaxies, their surroundings, and the wider cosmos. The circumgalactic medium is the main exchange zone in this cycle.
Warm–hot intergalactic medium: Diffuse intergalactic gas at temperatures of roughly 10^5 to 10^7 kelvin. Its boundary with circumgalactic gas is difficult to define in extended halos.

Linked from 9 pages