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Accretion does not drive the turbulence in galactic discs

Hopkins, Philip F. and Kereš, Dušan and Murray, Norman (2013) Accretion does not drive the turbulence in galactic discs. Monthly Notices of the Royal Astronomical Society, 432 (4). pp. 2639-2646. ISSN 0035-8711. doi:10.1093/mnras/stt472.

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Rapid accretion of cold intergalactic gas plays a crucial role in getting gas into galaxies. It has been suggested that this gas accretion proceeds along narrow streams that might also directly drive the turbulence in galactic gas, dynamical disturbances and bulge formation. In cosmological simulations, however, it is impossible to isolate and hence disentangle the effect of cold stream accretion from internal instabilities and mergers. Moreover, in most current cosmological simulations, the phase structure and turbulence in the interstellar medium (ISM) arising from stellar feedback are treated in an approximate (subgrid) manner, so that the feedback cannot generate turbulence in the ISM. In this paper we therefore test the effects of cold streams in extremely high-resolution simulations of otherwise isolated galaxy discs using detailed models for star formation and stellar feedback; we then include or exclude mock cold flows falling on to the galaxies, with mass accretion rates, velocities and flow geometry set to maximize their effect on the gaseous disc. We find (1) turbulent velocity dispersions in gas discs are identical with or without the presence of the cold flow; the energy injected by the flow is efficiently dissipated where it meets the disc. (2) In runs without stellar feedback, the presence of a cold flow has essentially no effect on runaway fragmentation (local collapse), resulting in star formation rates (SFRs) that are an order-of-magnitude too large. (3) Model discs in runs with both explicit feedback and cold flows have higher SFRs, but only insofar as they have more gas. (4) Because the flows are extended, relative to the size of the disc, they do not trigger strong resonant responses and so induce weak gross morphological perturbation (bulge formation via instabilities/fragmentation is not accelerated). (5) However, flows can thicken the disc by direct contribution of out-of-plane or misaligned star-forming streams/filaments. We conclude that while inflows are critical over cosmological time-scales to determine the supply and angular momentum of gas discs, they have weak instantaneous dynamical effects on galaxies.

Item Type:Article
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URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Kereš, Dušan0000-0002-1666-7067
Additional Information:© 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2013 March 10. Received 2013 February 26; in original form 2012 December 29. First published online: May 22, 2013. 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. NM is supported in part by NSERC and by the Canada Research Chairs program. DK acknowledges support from NASA through Hubble Fellowship grant HST-HF-51276.01-A.
Funding AgencyGrant Number
NASA Einstein FellowshipPF1-120083
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Canada Research Chairs programUNSPECIFIED
Subject Keywords:galaxies: active; galaxies: evolution; galaxies: formation; galaxies: star formation; cosmology: theory
Issue or Number:4
Record Number:CaltechAUTHORS:20130805-101243638
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39759
Deposited On:06 Aug 2013 14:25
Last Modified:09 Nov 2021 23:46

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