Journal Article

Properties of gas in and around galaxy haloes

Freeke van de Voort and Joop Schaye

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 4, pages 2991-3010
Published in print July 2012 | ISSN: 0035-8711
Published online July 2012 | e-ISSN: 1365-2966 | DOI:
Properties of gas in and around galaxy haloes

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We study the properties of gas inside and around galaxy haloes as a function of radius and halo mass, focusing mostly on z= 2, but also showing some results for z= 0. For this purpose, we use a suite of large cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations project. The properties of cold- and hot-mode gas, which we separate depending on whether the temperature has been higher than 105.5 K while it was extragalactic, are clearly distinguishable in the outer parts of massive haloes (virial temperatures ≫105 K). The differences between cold- and hot-mode gas resemble those between inflowing and outflowing gas. The cold-mode gas is mostly confined to clumpy filaments that are approximately in pressure equilibrium with the diffuse, hot-mode gas. Besides being colder and denser, cold-mode gas typically has a much lower metallicity and is much more likely to be infalling. However, the spread in the properties of the gas is large, even for a given mode and a fixed radius and halo mass, which makes it impossible to make strong statements about individual gas clouds. Metal-line cooling causes a strong cooling flow near the central galaxy, which makes it hard to distinguish gas accreted through the cold and hot modes in the inner halo. Stronger feedback results in larger outflow velocities and pushes hot-mode gas to larger radii. The gas properties evolve as expected from virial arguments, which can also account for the dependence of many gas properties on halo mass. We argue that cold streams penetrating hot haloes are observable as high column density H i Lyman α absorption systems in sightlines near massive foreground galaxies.

Keywords: galaxies: evolution; galaxies: formation; galaxies: haloes; intergalactic medium; cosmology: theory

Journal Article.  15382 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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