Molecular gas cloud properties at z ≃ 1 revealed by the superb angular resolution achieved with ALMA and gravitational lensing

Miroslava Dessauges-Zavadsky, Johan Richard, Françoise Combes, Matteo Messa, David Nagy, Lucio Mayer, Daniel Schaerer, Eiichi Egami, Angela Adamo

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Current observations favour that the massive ultraviolet-bright clumps with a median stellar mass of ∼ 107 M⊙, ubiquitously observed in z ∼1-3 galaxies, are star-forming regions formed in situ in galaxies. It has been proposed that they result from gas fragmentation due to gravitational instability of gas-rich, turbulent, and high-redshift discs. We bring support to this scenario by reporting the new discovery of giant molecular clouds (GMCs) in the strongly lensed, clumpy, main-sequence galaxy, A521-sys1, at z = 1.043. Its CO(4-3) emission was mapped with the Atacama Large Millimetre/submillimetre Array (ALMA) at an angular resolution of 0.19 × 0.16 arcsec2, reading down to 30 pc, thanks to gravitational lensing. We identified 14 GMCs, most being virialized, with 105.9-107.9 M⊙ masses and a median 800 M⊙ pc-2 molecular gas mass surface density, that are, respectively, 100 and 10 times higher than for nearby GMCs. They are also characterized by 10 times higher supersonic turbulence with a median Mach number of 60. They end up to fall above the Larson scaling relations, similarly to the GMCs in another clumpy z ≃ 1 galaxy, the Cosmic Snake, although differences between the two sets of high-redshift GMCs exist. Altogether they support that GMCs form with properties that adjust to the ambient interstellar medium conditions prevalent in the host galaxy whatever its redshift. The detected A521-sys1 GMCs are massive enough to be the parent gas clouds of stellar clumps, with a relatively high star formation efficiency per free-fall time of ∼11 per cent.

Original languageEnglish (US)
Pages (from-to)6222-6238
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Mar 1 2023


  • galaxies: ISM
  • galaxies: high-redshift
  • galaxies: individual: A521-sys1
  • galaxies: star formation
  • gravitational lensing: strong

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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