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Galaxy-wide outflows: cold gas and star formation at high speeds

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journal contribution
posted on 01.02.2016, 10:36 by K. Zubovas, Andrew Robert King
Several active galaxies show strong evidence for fast (v[Subscript: out] ∼ 1000 km s[Superscript: −1]) massive (M˙=M˙= several × 1000 M[Subscript: ⊙] yr[Superscript: −1]) gas outflows. Such outflows are expected on theoretical grounds once the central supermassive black hole reaches the mass set by the M-σ relation, and may be what makes galaxies become red and dead. Despite their high velocities, which imply temperatures far above those necessary for molecule dissociation, the outflows contain large amounts of molecular gas. To understand this surprising result, we investigate the gas cooling and show that the outflows cannot stably persist in high-temperature states. Instead, the outflowing gas forms a two-phase medium, with cold dense molecular clumps mixed with hot tenuous gas, as observed. We also show that efficient cooling leads to star formation, providing an observable outflow signature. The central parts of the outflows can be intrinsically luminous gamma-ray sources, provided that the central black hole is still strongly accreting. We note also that these outflows can persist for ∼108 yr after the central AGN has turned off, so that many observed outflows (particularly with high speeds) otherwise assumed to be driven by starbursts might also be of this type.

History

Citation

Monthly Notices Of The Royal Astronomical Society, 2014, 439 (1), pp. 400-406 (7)

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Monthly Notices Of The Royal Astronomical Society

Publisher

Oxford University Press (OUP)

issn

0035-8711

eissn

1365-2966

Acceptance date

19/12/2013

Copyright date

2014

Available date

01/02/2016

Publisher version

http://mnras.oxfordjournals.org/content/439/1/400

Language

en