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Dense molecular gas: a sensitive probe of stellar feedback models

Hopkins, Philip F. and Narayanan, Desika and Murray, Norman and Quataert, Eliot (2013) Dense molecular gas: a sensitive probe of stellar feedback models. Monthly Notices of the Royal Astronomical Society, 433 (1). pp. 69-77. ISSN 0035-8711. doi:10.1093/mnras/stt688.

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We show that the mass fraction of giant molecular cloud (GMC) gas (n ≳ 100 cm⁻³) in dense (n ≫ 10⁴ cm⁻³) star-forming clumps, observable in dense molecular tracers (L_(HCN)/L_(CO(1–0))), is a sensitive probe of the strength and mechanism(s) of stellar feedback, as well as the star formation efficiencies in the most dense gas. Using high-resolution galaxy-scale simulations with pc-scale resolution and explicit models for feedback from radiation pressure, photoionization heating, stellar winds and supernovae (SNe), we make predictions for the dense molecular gas tracers as a function of GMC and galaxy properties and the efficiency of stellar feedback/star formation. In models with weak/no feedback, much of the mass in GMCs collapses into dense subunits, predicting L_(HCN)/L_(CO(1–0)) ratios order-of-magnitude larger than observed. By contrast, models with feedback properties taken directly from stellar evolution calculations predict dense gas tracers in good agreement with observations. Changing the strength or timing of SNe tends to move systems along, rather than off, the L_(HCN)–L_(CO) relation (because SNe heat lower density material, not the high-density gas). Changing the strength of radiation pressure (which acts efficiently in the highest density gas), however, has a much stronger effect on L_(HCN) than on L_(CO). We show that degeneracies between the strength of feedback, and efficiency of star formation on small scales, can be broken by the combination of dense gas, intermediate-density gas and total star formation rate (SFR) tracers, and favour models where the galaxy-integrated star formation efficiency in dense gas is low. We also predict that the fraction of dense gas (_(LHCN)/L_(CO(1–0))) increases with increasing GMC surface density; this drives a trend in L_(HCN)/L_(CO(1–0)) with SFR and luminosity which has tentatively been observed. Our results make specific predictions for enhancements in the dense gas tracers in unusually dense environments such as ultraluminous infrared galaxies and galactic nuclei (including the galactic centre).

Item Type:Article
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URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Narayanan, Desika0000-0002-7064-4309
Quataert, Eliot0000-0001-9185-5044
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 August 23. We thank the anonymous referee for a number of helpful suggestions. Support for PFH was provided by NASA through Einstein Post-doctoral 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. DN acknowledges partial support from the NSF via grant AST-1009452. 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, galaxies: star formation, cosmology: theory
Issue or Number:1
Record Number:CaltechAUTHORS:20200522-113948802
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Official Citation:Philip F. Hopkins, Desika Narayanan, Norman Murray, Eliot Quataert, Dense molecular gas: a sensitive probe of stellar feedback models, Monthly Notices of the Royal Astronomical Society, Volume 433, Issue 1, 21 July 2013, Pages 69–77,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103407
Deposited By: George Porter
Deposited On:22 May 2020 21:53
Last Modified:16 Nov 2021 18:21

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