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Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium

Hopkins, Philip F. and Cox, Thomas J. and Hernquist, Lars and Narayanan, Desika and Hayward, Christopher C. and Murray, Norman (2013) Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium. Monthly Notices of the Royal Astronomical Society, 430 (3). pp. 1901-1927. ISSN 1365-2966.

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We use hydrodynamic simulations with detailed, explicit models for stellar feedback to study galaxy mergers. These high-resolution (∼1 pc) simulations follow the formation and destruction of individual giant molecular clouds (GMC) and star clusters. We find that the final starburst is dominated by in situ star formation, fuelled by gas which flows inwards due to global torques. The resulting high gas density results in rapid star formation. The gas is self-gravitating, and forms massive (≲10¹⁰ M_⊙) GMC and subsequently super star clusters (with masses up to 10⁸ M_⊙). However, in contrast to some recent simulations, the bulk of new stars which eventually form the central bulge are not born in super-clusters which then sink to the centre of the galaxy. This is because feedback efficiently disperses GMC after they turn several per cent of their mass into stars. In other words, most of the mass that reaches the nucleus does so in the form of gas. The Kennicutt–Schmidt law emerges naturally as a consequence of feedback balancing gravitational collapse, independent of the small-scale star formation microphysics. The same mechanisms that drive this relation in isolated galaxies, in particular radiation pressure from infrared photons, extend, with no fine-tuning, over seven decades in star formation rate (SFR) to regulate star formation in the most extreme starburst systems with densities ≳10⁴ M_⊙ pc⁻². This feedback also drives super-winds with large mass-loss rates; however, a significant fraction of the wind material falls back on to the discs at later times, leading to higher post-starburst SFRs in the presence of stellar feedback. This suggests that strong active galactic nucleus feedback may be required to explain the sharp cut-offs in SFR that are observed in post-merger galaxies. We compare the results to those from simulations with no explicit resolution of GMC or feedback [‘effective equation-of-state’ (EOS) models]. We find that global galaxy properties are similar between EOS and resolved-feedback models. The relic structure and mass profile, and the total mass of stars formed in the nuclear starburst are quite similar, as is the morphological structure during and after mergers (tails, bridges, etc.). Disc survival in sufficiently gas rich mergers is similar in the two cases, and the new models follow the same scalings as derived for the efficiency of disc re-formation after a merger as derived from previous work with the simplified EOS models. While the global galaxy properties are similar between EOS and feedback models, subgalaxy-scale properties and the SFRs can be quite different: the more detailed models exhibit significantly higher star formation in tails and bridges (especially in shocks), and allow us to resolve the formation of super star clusters. In the new models, the star formation is more strongly time-variable and drops more sharply between close passages. The instantaneous burst enhancement can be higher or lower, depending on the details of the orbit and initial structural properties of the galaxies; first-passage bursts are more sensitive to these details than those at the final coalescence.

Item Type:Article
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URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
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 January 2. Received 2012 November 13; in original form 2012 May 23. We thank Eliot Quataert for helpful discussions and contributions motivating this work, and our referee, Matthias Steinmetz, for several useful 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 NASA under contract NAS8-03060.
Funding AgencyGrant Number
NASA Einstein FellowshipPF1-120083
Subject Keywords:galaxies: active, galaxies: evolution, galaxies: formation, galaxies: star formation, cosmology: theory
Issue or Number:3
Record Number:CaltechAUTHORS:20200522-113949119
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Official Citation:Philip F. Hopkins, Thomas J. Cox, Lars Hernquist, Desika Narayanan, Christopher C. Hayward, Norman Murray, Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium, Monthly Notices of the Royal Astronomical Society, Volume 430, Issue 3, 11 April 2013, Pages 1901–1927,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103410
Deposited By: George Porter
Deposited On:22 May 2020 21:39
Last Modified:22 May 2020 21:39

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