The ALPINE-ALMA [C II] survey. Molecular gas budget in the early Universe as traced by [C II]
Journal
Date Issued
2020
Author(s)
Dessauges-Zavadsky, M.
•
Ginolfi, M.
•
Pozzi, F.
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Béthermin, M.
•
Le Fèvre, O.
•
Fujimoto, S.
•
Silverman, J. D.
•
Jones, G. C.
•
•
Schaerer, D.
•
Faisst, A. L.
•
Khusanova, Y.
•
Fudamoto, Y.
•
Cassata, P.
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Loiacono, F.
•
Capak, P. L.
•
Yan, L.
•
Amorin, R.
•
•
Boquien, M.
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Cimatti, A.
•
•
Hathi, N. P.
•
Ibar, E.
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Koekemoer, A. M.
•
Lemaux, B. C.
•
Narayanan, D.
•
Oesch, P. A.
•
Rodighiero, G.
•
Romano, M.
•
Talia, M.
•
Toft, S.
•
•
Zamorani, G.
•
Abstract
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 high redshifts. We use the [C II] 158 μm luminosity, which was 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 survey. The agreement between the 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 between two and three shorter than in present-day galaxies. This suggests a mild enhancement of the star formation efficiency toward high redshifts. Our estimates also show that the previously reported rise in the molecular gas fraction 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 that of the specific star formation rate. We use multi-epoch abundance-matching to follow the gas fraction evolution across 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 increase of the gas fraction with redshift, while the latter show a steep rise from z = 0 to z ∼ 2 followed by a constant gas fraction from z ∼ 2 to z = 5.9. We discuss three possible effects, namely outflows, a pause in gas supply, and over-efficient star formation, which may jointly contribute to the gas fraction plateau of the latter massive galaxies.
Volume
643
Start page
A5
Issn Identifier
0004-6361
Ads BibCode
2020A&A...643A...5D
Rights
open.access
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