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Resolving the generation of starburst winds in Galaxy mergers

Hopkins, Philip F. and Kereš, Dušan and Murray, Norman and Hernquist, Lars and Narayanan, Desika and Hayward, Christopher C. (2013) Resolving the generation of starburst winds in Galaxy mergers. Monthly Notices of the Royal Astronomical Society, 433 (1). pp. 78-97. ISSN 0035-8711.

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We study galaxy superwinds driven in major mergers, using pc-scale resolution simulations with detailed models for stellar feedback that can self-consistently follow the generation of winds. The models include molecular cooling, star formation at high densities in giant molecular clouds, and gas recycling and feedback from supernovae (I and II), stellar winds and radiation pressure. We study mergers of systems from Small-Magellanic-Cloud-like dwarfs and Milky Way analogues to z ∼ 2 starburst discs. Multiphase superwinds are generated in all passages, with outflow rates up to ∼1000 M⊙ yr^(−1). However, the wind mass-loading efficiency (outflow rate divided by star formation rate, SFR) is similar to that in the isolated galaxy counterparts of each merger: it depends more on global galaxy properties (mass, size and escape velocity) than on the dynamical state or orbital parameters of the merger. Winds tend to be bi- or unipolar, but multiple ‘events’ build up complex morphologies with overlapping, differently oriented bubbles and shells at a range of radii. The winds have complex velocity and phase structure, with material at a range of speeds up to ∼1000 km s^(−1) (forming a Hubble-like flow), and a mix of molecular, ionized and hot gas that depends on galaxy properties. We examine how these different phases are connected to different feedback mechanisms. These simulations resolve a problem in some ‘subgrid’ models, where simple wind prescriptions can dramatically suppress merger-induced starbursts, often making it impossible to form Ultra Luminous Infrared Galaxies (ULIRGs). Despite large mass-loading factors (≳10–20) in the winds simulated here, the peak SFRs are comparable to those in ‘no wind’ simulations. Wind acceleration does not act equally, so cold dense gas can still lose angular momentum and form stars, while these stars blow out gas that would not have participated in the starburst in the first place. Considerable wind material is not unbound, and falls back on the disc at later times post-merger, leading to higher post-starburst SFRs in the presence of stellar feedback. We consider different simulation numerical methods and their effects on the wind phase structure; while most results are converged, we find that the existence of small clumps in the outflow at large distances from the galaxy is quite sensitive to the methodology.

Item Type:Article
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URLURL TypeDescription DOIArticle Paper
Hopkins, Philip F.0000-0003-3729-1684
Kereš, Dušan0000-0002-1666-7067
Hernquist, Lars0000-0001-6950-1629
Narayanan, Desika0000-0002-7064-4309
Hayward, Christopher C.0000-0003-4073-3236
Additional Information:© 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2013 April 19. Received 2013 April 18; in original form 2012 December 30. First published online: June 3, 2013. We thank Eliot Quataert for helpful discussions and contributions motivating this work, and thank the anonymous referee and editor for insightful comments and suggestions. Support for PFH was provided by NASA through Einstein Postdoctoral Fellowship Award Number PF1-120083 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the NASA under contract NAS8-03060. EQ is supported in part by NASA grant NNG06GI68G and the David and Lucile Packard Foundation.
Funding AgencyGrant Number
NASA Einstein FellowshipPF1-120083
David and Lucile Packard FoundationUNSPECIFIED
Subject Keywords:galaxies: active; galaxies: evolution; galaxies: formation; cosmology: theory
Issue or Number:1
Record Number:CaltechAUTHORS:20130923-104112297
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41477
Deposited By: Tony Diaz
Deposited On:23 Sep 2013 17:48
Last Modified:06 Nov 2019 03:54

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