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Submillimetre compactness as a critical dimension to understand the Main Sequence of star-forming galaxies

Puglisi, Annagrazia; Daddi, Emanuele; Valentino, Francesco; Magdis, Georgios; Liu, Daizhong; Kokorev, Vasily; Circosta, Chiara; Elbaz, David Elbaz; Bournard, Frederic; Gomez-Guijarro, Carlos; Jin, Shuowen; Madden, Suzanne; Sargent, Mark T.; Swinbank, Mark

Submillimetre compactness as a critical dimension to understand the Main Sequence of star-forming galaxies Thumbnail


Emanuele Daddi

Francesco Valentino

Georgios Magdis

Daizhong Liu

Vasily Kokorev

Chiara Circosta

David Elbaz Elbaz

Frederic Bournard

Carlos Gomez-Guijarro

Shuowen Jin

Suzanne Madden

Mark T. Sargent


We study the interstellar medium (ISM) properties as a function of the molecular gas size for 77 infrared-selected galaxies at z ∼ 1.3, having stellar masses 109.4 . M? . 1012.0 M and star formation rates 12 . SFRFIR . 1000 M yr−1 . Molecular gas sizes are measured on ALMA images that combine CO(2-1), CO(5-4) and underlying continuum observations, and include CO(4-3), CO(7-6)+[CI](3P2 − 3 P1), [CI](3P1 − 3 P0) observations for a subset of the sample. The & 46% of our galaxies have a compact molecular gas reservoir, and lie below the optical disks mass-size relation. Compact galaxies on and above the main sequence have higher CO excitation and star formation efficiency than galaxies with extended molecular gas reservoirs, as traced by CO(5-4)/CO(2-1) and CO(2-1)/LIR,SF ratios. Average CO+[CI] spectral line energy distributions indicate higher excitation in compacts relative to extended sources. Using CO(2-1) and dust masses as molecular gas mass tracers, and conversion factors tailored to their ISM conditions, we measure lower gas fractions in compact main-sequence galaxies compared to extended sources. We suggest that the sub-millimetre compactness, defined as the ratio between the molecular gas and the stellar size, is an unavoidable information to be used with the main sequence offset to describe the ISM properties of galaxies, at least above M? > 1010.6 M, where our observations fully probe the main sequence scatter. Our results are consistent with mergers driving the gas in the nuclear regions, enhancing the CO excitation and star formation efficiency. Compact main-sequence galaxies are consistent with being an early post-starburst population following a merger-driven starburst episode, stressing the important role of mergers in the evolution of massive galaxies.

Journal Article Type Article
Acceptance Date Oct 4, 2021
Online Publication Date Oct 13, 2021
Publication Date 2021-12
Deposit Date Nov 8, 2021
Publicly Available Date Nov 8, 2021
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 508
Issue 4
Pages 5217-5238
Public URL


Accepted Journal Article (1.6 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021, The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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