The ALPINE-ALMA [C II] survey: Molecular gas budget in the early universe as traced by [C II]

M. Dessauges-Zavadsky, M. Ginolfi, F. Pozzi, M. Béthermin, O. Le Fèvre, S. Fujimoto, J. D. Silverman, G. C. Jones, D. Schaerer, A. L. Faisst, Y. Khusanova, Y. Fudamoto, P. Cassata, F. Loiacono, P. L. Capak, L. Yan, R. Amorin, S. Bardelli, M. Boquien, A. CimattiC. Gruppioni, N. P. Hathi, E. Ibar, A. M. Koekemoer, B. C. Lemaux, D. Narayanan, P. A. Oesch, G. Rodighiero, M. Romano, M. Talia, S. Toft, L. Vallini, D. Vergani, G. Zamorani, E. Zucca

Research output: Contribution to journalArticlepeer-review


The molecular gas content of normal galaxies at z > 4 is poorly constrained, because the commonly used molecular gas tracers become hard to detect at these redshifts. We use the [C ii] 158 µm luminosity, recently proposed as a molecular gas tracer, to estimate the molecular gas content in a large sample of main-sequence star-forming galaxies at z = 4.4 − 5.9, with a median stellar mass of 109.7 M , drawn from the ALMA Large Program to INvestigate [C ii] at Early times (ALPINE) survey. The good agreement between molecular gas masses derived from [C ii] luminosities, dynamical masses, and rest-frame 850 µm luminosities, extrapolated from the rest-frame 158 µm continuum, supports [C ii] as a reliable tracer of molecular gas in our sample. We find a continuous decline of the molecular gas depletion timescale from z = 0 to z = 5.9, which reaches a mean value of (4.6 ± 0.8) × 108 yr at z ∼ 5.5, only a factor of 2 − 3 shorter than in present-day galaxies. This suggests a mild enhancement of star formation efficiency toward high redshifts, unless the molecular gas fraction significantly increases. Our estimates show that the rise in molecular gas fraction as reported previously, flattens off above z ∼ 3.7 to achieve a mean value of 63% ± 3% over z = 4.4 − 5.9. This redshift evolution of the gas fraction is in line with the one of the specific star formation rate. We use multi-epoch abundance matching to follow the gas fraction evolution over cosmic time of progenitors of z = 0 Milky Way-like galaxies in ∼ 1013 M halos and of more massive z = 0 galaxies in ∼ 1014 M halos. Interestingly, the former progenitors show a monotonic decrease of the gas fraction with cosmic time, while the latter show a constant gas fraction from z = 5.9 to z ∼ 2 and a steep decrease at z. 2. We discuss three possible effects, namely outflows, halt of gas supplying, and over-efficient star formation, which may jointly contribute to the gas fraction plateau of the latter massive galaxies.

Original languageEnglish
JournalUnknown Journal
Publication statusPublished - 2020 Apr 22
Externally publishedYes


  • Galaxies: evolution
  • Galaxies: high-redshift
  • Galaxies: ISM
  • ISM: molecules

ASJC Scopus subject areas

  • General

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