Radiation Pressure Driven Galactic Winds from Self-Gravitating Disks

Details Radiation Pressure Driven Galactic Winds from Self-Gravitating Disks Radiation Pressure Driven Galactic Winds from Self-Gravitating Disks

2010-05-25

arxiv.org/abs/1005.4691v2

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

8 pages, 5 figures, updated in response to referee's comments

Scientific paper

We study large-scale winds driven from uniformly bright self-gravitating disks radiating near the Eddington limit. We show that the ratio of the radiation pressure force to the gravitational force increases with height to a maximum of twice its value at the disk surface. Thus, uniformly bright self-gravitating disks radiating at the Eddington limit are fundamentally unstable to driving large-scale winds. These results contrast with the spherically symmetric case, where super-Eddington luminosities are required for wind formation. We apply this theory to galactic winds from starburst galaxies that approach the Eddington limit for dust. For hydrodynamically coupled gas and dust, we find that the asymptotic velocity of the wind is v_infty ~ 3 v_ rot and that v_infinity ~ SFR^{0.36}, where v_rot is the mean disk rotation velocity and SFR is the star formation rate. However, both the gravitational potential of the surrounding dark matter halo and a (potentially massive) old stellar bulge act to decrease v_infty. A more realistic treatment shows that the flow can either be unbound, or bound, forming a "fountain flow" with a typical turning timescale of t_turn ~ 0.1-1 Gyr, depending on the ratio of the mass and radius of the starburst disk relative to the total mass and break radius of the dark matter halo or bulge. We provide quantitative criteria and scaling relations for assessing whether or not a starburst of given properties can drive unbound flows via the mechanism described in this paper. Importantly, we note that because t_ turn is longer than the star formation timescale in the starbursts and ultra-luminous infrared galaxies for which our theory is most applicable, if starbursts are selected as such, they may be observed to have strong outflows along the line of sight with a maximum velocity v_ max comparable to 3 v_ rot, even though their winds are in fact bound on large scales.

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