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Molecular clouds in the Cosmic Snake normal star-forming galaxy 8 billion years ago


Abstract

The cold molecular gas in contemporary galaxies is structured in discrete cloud complexes. These giant molecular clouds (GMCs), with 104–107 solar masses (M⊙) and radii of 5–100 parsecs, are the seeds of star formation1. Highlighting the molecular gas structure at such small scales in distant galaxies is observationally challenging. Only a handful of molecular clouds were reported in two extreme submillimetre galaxies at high redshift2,3,4. Here we search for GMCs in a typical Milky Way progenitor at z = 1.036. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we mapped the CO(4–3) emission of this gravitationally lensed galaxy at high resolution, reading down to 30 parsecs, which is comparable to the resolution of CO observations of nearby galaxies5. We identify 17 molecular clouds, characterized by masses, surface densities and supersonic turbulence all of which are 10–100 times higher than present-day analogues. These properties question the universality of GMCs6 and suggest that GMCs inherit their properties from ambient interstellar medium. The measured cloud gas masses are similar to the masses of stellar clumps seen in the galaxy in comparable numbers7. This corroborates the formation of molecular clouds by fragmentation of distant turbulent galactic gas disks8,9, which then turn into stellar clumps ubiquitously observed in galaxies at ‘cosmic noon’ (ref. 10).

Abstract

The cold molecular gas in contemporary galaxies is structured in discrete cloud complexes. These giant molecular clouds (GMCs), with 104–107 solar masses (M⊙) and radii of 5–100 parsecs, are the seeds of star formation1. Highlighting the molecular gas structure at such small scales in distant galaxies is observationally challenging. Only a handful of molecular clouds were reported in two extreme submillimetre galaxies at high redshift2,3,4. Here we search for GMCs in a typical Milky Way progenitor at z = 1.036. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we mapped the CO(4–3) emission of this gravitationally lensed galaxy at high resolution, reading down to 30 parsecs, which is comparable to the resolution of CO observations of nearby galaxies5. We identify 17 molecular clouds, characterized by masses, surface densities and supersonic turbulence all of which are 10–100 times higher than present-day analogues. These properties question the universality of GMCs6 and suggest that GMCs inherit their properties from ambient interstellar medium. The measured cloud gas masses are similar to the masses of stellar clumps seen in the galaxy in comparable numbers7. This corroborates the formation of molecular clouds by fragmentation of distant turbulent galactic gas disks8,9, which then turn into stellar clumps ubiquitously observed in galaxies at ‘cosmic noon’ (ref. 10).

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute for Computational Science
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Physical Sciences > Astronomy and Astrophysics
Language:English
Date:1 December 2019
Deposited On:14 Feb 2020 08:21
Last Modified:29 Jul 2020 13:42
Publisher:Springer
ISSN:2397-3366
OA Status:Closed
Publisher DOI:https://doi.org/10.1038/s41550-019-0874-0

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