1932

Abstract

Galactic halo gas traces inflowing star-formation fuel and feedback from a galaxy's disk and is therefore crucial to our understanding of galaxy evolution. In this review, we summarize the multiwavelength observational properties and origin models of Galactic and low-redshift spiral galaxy halo gas. Galactic halos contain multiphase gas flows that are dominated in mass by the ionized component and extend to large radii. The densest, coldest halo gas observed in neutral hydrogen (H) is generally closest to the disk (<20 kpc), and absorption line results indicate warm and warm-hot diffuse halo gas is present throughout a galaxy's halo. The hot halo gas detected is not a significant fraction of a galaxy's baryons. The disk-halo interface is where the multiphase flows are integrated into the star-forming disk, and there is evidence for both feedback and fueling at this interface from its temperature and kinematic gradients, and H structures.

The origin and fate of halo gas are considered in the context of cosmological and idealized local simulations. Accretion along cosmic filaments occurs in both hot (>105.5 K) and cold modes in simulations, with the compressed material close to the disk being the coldest and densest, in agreement with observations. There is evidence in halo gas observations for radiative and mechanical feedback mechanisms, including escaping photons from the disk, supernova-driven winds, and a galactic fountain. Satellite accretion also leaves behind abundant halo gas. This satellite gas interacts with the existing halo medium, and much of this gas will become part of the diffuse halo before it reaches the disk. The accretion rate from cold and warm halo gas is generally below a galaxy disk's star-formation rate, but gas at the disk-halo interface and stellar feedback may be important additional fuel sources.

[Erratum, Closure]

An erratum has been published for this article:
Gaseous Galaxy Halos
Loading

Article metrics loading...

/content/journals/10.1146/annurev-astro-081811-125612
2012-09-22
2024-03-28
Loading full text...

Full text loading...

/content/journals/10.1146/annurev-astro-081811-125612
Loading
/content/journals/10.1146/annurev-astro-081811-125612
Loading

Data & Media loading...

  • Article Type: Review Article
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error