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Published February 2020 | Accepted Version + Published
Journal Article Open

Evolution of giant molecular clouds across cosmic time


Giant molecular clouds (GMCs) are well studied in the local Universe, however, exactly how their properties vary during galaxy evolution is poorly understood due to challenging resolution requirements, both observational and computational. We present the first time-dependent analysis of GMCs in a Milky Way-like galaxy and an Large Magellanic Cloud (LMC)-like dwarf galaxy of the FIRE-2 (Feedback In Realistic Environments) simulation suite, which have sufficient resolution to predict the bulk properties of GMCs in cosmological galaxy formation self-consistently. We show explicitly that the majority of star formation outside the galactic centre occurs within self-gravitating gas structures that have properties consistent with observed bound GMCs. We find that the typical cloud bulk properties such as mass and surface density do not vary more than a factor of 2 in any systematic way after the first Gyr of cosmic evolution within a given galaxy from its progenitor. While the median properties are constant, the tails of the distributions can briefly undergo drastic changes, which can produce very massive and dense self-gravitating gas clouds. Once the galaxy forms, we identify only two systematic trends in bulk properties over cosmic time: a steady increase in metallicity produced by previous stellar populations and a weak decrease in bulk cloud temperatures. With the exception of metallicity, we find no significant differences in cloud properties between the Milky Way-like and dwarf galaxies. These results have important implications for cosmological star and star cluster formation and put especially strong constraints on theories relating the stellar initial mass function to cloud properties.

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 (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2019 December 10. Received 2019 December 6; in original form 2019 October 3. Published: 17 December 2019. The authors would like to thank Philip F. Hopkins for his helpful comments. This work used computational resources of the University of Texas at Austin and the Texas Advanced Computing Center (TACC; http://www.tacc.utexas.edu). DG is supported by the Harlan J. Smith McDonald Observatory Postdoctoral Fellowship. MYG is supported by a CIERA Postoctoral Fellowship. SSRO is supported by NSF Career Award AST-1650486 and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. MBK acknowledges support from NSF grant no. AST-1517226 and CAREER grant no. AST-1752913 and from NASA grant nos NNX17AG29G and HST-AR-14282, HST-AR-14554, HST-AR-15006, and HST-GO-14191 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. CAFG was supported by NSF through grant nos AST-1517491, AST-1715216, and CAREER award AST-1652522, by NASA through grant nos NNX15AB22G and 17-ATP17-0067, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. AW received support from NASA, through ATP grant no. 80NSSC18K1097 and HST grant nos GO-14734 and AR-15057 from STScI, a Hellman Fellowship from UC Davis, and the Heising-Simons Foundation. Support for SRL was provided by NASA through Hubble Fellowship grant no. HST-JF2-51395.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.

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Accepted Version - 1910.01163.pdf


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August 19, 2023
October 19, 2023