Title:	Galactic winds driven by cosmic ray streaming
Authors:	Uhlig, M. Pfrommer, C. Sharma, Mahavir Nath, Biman B. Ensslin, T.A. Springel, V.
Keywords:	galaxies: dwarf galaxies: evolution galaxies: formation intergalactic medium galaxies: starburst
Issue Date:	Jul-2012
Publisher:	Wiley Interscience for the RAS
Citation:	Monthly Notices of the Royal Astronomical Society, 2012, Vol. 423, p. 2374-2396
Abstract:	Galactic winds are observed in many spiral galaxies with sizes from dwarfs up to the Milky Way, and they sometimes carry a mass in excess of that of newly formed stars by up to a factor of ten. Multiple driving processes of such winds have been proposed, including thermal pressure due to supernova-heating, UV radiation pressure on dust grains, or cosmic ray (CR) pressure. We here study wind formation due to CR physics using a numerical model that accounts for CR acceleration by supernovae, CR thermalization, and advective CR transport. In addition, we introduce a novel implementation of CR streaming relative to the rest frame of the gas. We find that CR streaming drives powerful and sustained winds in galaxies with virial masses M_200 < 10^{11} Msun. In dwarf galaxies (M_200 ~ 10^9 Msun) the winds reach a mass loading factor of ~5, expel ~60 per cent of the initial baryonic mass contained inside the halo's virial radius and suppress the star formation rate by a factor of ~5. In dwarfs, the winds are spherically symmetric while in larger galaxies the outflows transition to bi-conical morphologies that are aligned with the disc's angular momentum axis. We show that damping of Alfven waves excited by streaming CRs provides a means of heating the outflows to temperatures that scale with the square of the escape speed. In larger haloes (M_200 > 10^{11} Msun), CR streaming is able to drive fountain flows that excite turbulence. For halo masses M_200 > 10^{10} Msun, we predict an observable level of H-alpha and X-ray emission from the heated halo gas. We conclude that CR-driven winds should be crucial in suppressing and regulating the first epoch of galaxy formation, expelling a large fraction of baryons, and - by extension - aid in shaping the faint end of the galaxy luminosity function. They should then also be responsible for much of the metal enrichment of the intergalactic medium.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/4778
ISSN:	0035-8711 1365-2966 (Online)
Alternative Location:	http://adsabs.harvard.edu/doi/10.1111/j.1365-2966.2012.21045.x http://arxiv.org/abs/1203.1038 http://dx.doi.org/10.1111/j.1365-2966.2012.21045.x
Copyright:	2012 The authors & the Royal Astronomical Society.
Appears in Collections:	Research Papers (A&A)

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