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Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF?

Guszejnov, Dávid and Hopkins, Philip F. and Graus, Andrew S. (2019) Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF? Monthly Notices of the Royal Astronomical Society, 485 (4). pp. 4852-4862. ISSN 0035-8711. doi:10.1093/mnras/stz736.

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One of the most robust observations of the stellar initial mass function (IMF) is its near-universality in the Milky Way and neighbouring galaxies. But recent observations of early-type galaxies can be interpreted to imply a ‘bottom-heavy’ IMF, while others of ultrafaint dwarfs could imply a ‘top-heavy’ IMF. This would impose powerful constraints on star formation models. We explore what sort of ‘cloud-scale’ IMF models could possibly satisfy these constraints. We utilize simulated galaxies that reproduce (broadly) the observed galaxy properties, while they also provide the detailed star formation history and properties of each progenitor star-forming cloud. We then consider generic models where the characteristic mass of the IMF is some arbitrary power-law function of progenitor cloud properties, along with well-known literature IMF models which scale with Jeans mass, ‘turbulent Bonnor–Ebert mass’, temperature, the opacity limit, metallicity, or the ‘protostellar heating mass’. We show that no IMF models currently in the literature – nor any model where the turnover mass is an arbitrary power-law function of a combination of cloud temperature/density/size/metallicity/velocity dispersion/magnetic field – can reproduce the claimed IMF variation in ellipticals or dwarfs without severely violating observational constraints in the Milky Way. Specifically, they predict too much variation in the ‘extreme’ environments of the Galaxy compared to that observed. Either the IMF varies in a more complicated manner, or alternative interpretations of the extragalactic observations must be explored.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Guszejnov, Dávid0000-0001-5541-3150
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 March 4. Received 2019 March 4; in original form 2019 February 8. Support for DG and PFH was provided by an Alfred P. Sloan Research Fellowship, NSF Collaborative Research grant #1715847 and CAREER grant #1455342, and NASA grants NNX15AT06G, JPL 1589742, 17-ATP17-0214. Numerical calculations were run on the Caltech compute cluster ‘Wheeler,’ allocations from XSEDE TG-AST130039 and PRAC NSF.1713353 supported by the NSF, and NASA HEC SMD-16-7592. This work used computational resources of the University of Texas at Austin and the Texas Advanced Computing Center (TACC;, the NASA Advanced Supercomputing (NAS) Division and the NASA Center for Climate Simulation (NCCS). DG and ASG were supported by the Harlan J. Smith McDonald Observatory Postdoctoral Fellowship. We would like to thank Stella Offner, Daniel Anglés-Alcázar, and Alexa Villaume for their help and comments.
Group:Astronomy Department
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
Harlan J. Smith McDonald ObservatoryUNSPECIFIED
Subject Keywords:turbulence, stars: formation, galaxies: star formation, cosmology: theory
Issue or Number:4
Record Number:CaltechAUTHORS:20190725-125944080
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Official Citation:Dávid Guszejnov, Philip F Hopkins, Andrew S Graus, Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF?, Monthly Notices of the Royal Astronomical Society, Volume 485, Issue 4, June 2019, Pages 4852–4862,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97412
Deposited By: George Porter
Deposited On:25 Jul 2019 20:46
Last Modified:16 Nov 2021 17:31

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