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A Simple Non-equilibrium Feedback Model for Galaxy-Scale Star Formation: Delayed Feedback and SFR Scatter

Orr, Matthew E. and Hayward, Christopher C. and Hopkins, Philip F. (2019) A Simple Non-equilibrium Feedback Model for Galaxy-Scale Star Formation: Delayed Feedback and SFR Scatter. Monthly Notices of the Royal Astronomical Society, 486 (4). pp. 4724-4737. ISSN 0035-8711. doi:10.1093/mnras/stz1156.

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We explore a class of simple non-equilibrium star formation models within the framework of a feedback-regulated model of the ISM, applicable to kiloparsec-scale resolved star formation relations (e.g. Kennicutt–Schmidt). Combining a Toomre-Q-dependent local star formation efficiency per free-fall time with a model for delayed feedback, we are able to match the normalization and scatter of resolved star formation scaling relations. In particular, this simple model suggests that large (∼dex) variations in star formation rates (SFRs) on kiloparsec scales may be due to the fact that supernova feedback is not instantaneous following star formation. The scatter in SFRs at constant gas surface density in a galaxy then depends on the properties of feedback and when we observe its star-forming regions at various points throughout their collapse/star formation ‘cycles’. This has the following important observational consequences: (1) the scatter and normalization of the Kennicutt–Schmidt relation are relatively insensitive to the local (small-scale) star formation efficiency; (2) but gas depletion times and velocity dispersions are; (3) the scatter in and normalization of the Kennicutt–Schmidt relation is a sensitive probe of the feedback time-scale and strength; (4) even in a model where ˜Q_(gas) deterministically dictates star formation locally, time evolution, variation in local conditions (e.g. gas fractions and dynamical times), and variations between galaxies can destroy much of the observable correlation between SFR and ˜Q_(gas) in resolved galaxy surveys. Additionally, this model exhibits large scatter in SFRs at low gas surface densities, in agreement with observations of flat outer H I disc velocity dispersion profiles.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Orr, Matthew E.0000-0003-1053-3081
Hayward, Christopher C.0000-0003-4073-3236
Hopkins, Philip F.0000-0003-3729-1684
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 April 25. Received 2019 April 22; in original form 2018 October 22. MEO is grateful for the encouragement of his late father, SRO, in studying astrophysics. We are grateful to the anonymous referee for providing us with constructive comments and suggestions that greatly improved the quality of this work. MEO is supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1144469. The Flatiron Institute is supported by the Simons Foundation. Support for PFH was provided by an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant #1411920 and CAREER Grant #1455342. This research has used NASA’s Astrophysics Data System.
Group:TAPIR, Astronomy Department
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1144469
Simons FoundationUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords:ISM: evolution – ISM: kinematics and dynamics – galaxies: ISM– galaxies: star formation
Issue or Number:4
Record Number:CaltechAUTHORS:20190206-105614389
Persistent URL:
Official Citation:Matthew E Orr, Christopher C Hayward, Philip F Hopkins, A simple non-equilibrium feedback model for galaxy-scale star formation: delayed feedback and SFR scatter, Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 4, July 2019, Pages 4724–4737,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92723
Deposited By: George Porter
Deposited On:08 Feb 2019 15:32
Last Modified:16 Nov 2021 03:53

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