TY - JOUR

T1 - The ALMA REBELS Survey

T2 - The Cosmic H i Gas Mass Density in Galaxies at z approximate to 7

AU - Heintz, K. E.

AU - Oesch, P. A.

AU - Aravena, M.

AU - Bouwens, R. J.

AU - Dayal, P.

AU - Ferrara, A.

AU - Fudamoto, Y.

AU - Graziani, L.

AU - Inami, H.

AU - Sommovigo, L.

AU - Smit, R.

AU - Stefanon, M.

AU - Topping, M.

AU - Pallottini, A.

AU - van der Werf, P.

PY - 2022/8/1

Y1 - 2022/8/1

N2 - The neutral atomic gas content of individual galaxies at large cosmological distances has until recently been difficult to measure due to the weakness of the hyperfine H I 21 cm transition. Here we estimate the H I gas mass of a sample of main-sequence star-forming galaxies at z similar to 6.5-7.8 surveyed for [C II] 158 mu m emission as part of the Reionization Era Bright Emission Line Survey (REBELS), using a recent calibration of the [C II]-to-H I conversion factor. We find that the H I gas mass excess in galaxies increases as a function of redshift, with an average of M-HI /M-star approximate to 10, corresponding to H I gas mass fractions of f(HI) = M-HI /(M-star + M-HI) = 90%, at z approximate to 7. Based on the [C II] 158 mu m luminosity function (LF) derived from the same sample of galaxies, we further place constraints on the cosmic H I gas mass density in galaxies (rho(HI)) at this redshift, which we measure to be rho(HI) = 7.1(-3.0)(+6.4) x 10(6) M-circle dot Mpc(-3). This estimate is substantially lower by a factor of approximate to 10 than that inferred from an extrapolation of damped Ly alpha absorber (DLA) measurements and largely depends on the exact [C II] LF adopted. However, we find this decrease in rho(HI) to be consistent with recent simulations and argue that this apparent discrepancy is likely a consequence of the DLA sight lines predominantly probing the substantial fraction of H I gas in high-z galactic halos, whereas [C II] traces the H I in the ISM associated with star formation. We make predictions for this buildup of neutral gas in galaxies as a function of redshift, showing that at z greater than or similar to 5, only approximate to 10% of the cosmic H I gas content is confined in galaxies and associated with the star-forming ISM.

AB - The neutral atomic gas content of individual galaxies at large cosmological distances has until recently been difficult to measure due to the weakness of the hyperfine H I 21 cm transition. Here we estimate the H I gas mass of a sample of main-sequence star-forming galaxies at z similar to 6.5-7.8 surveyed for [C II] 158 mu m emission as part of the Reionization Era Bright Emission Line Survey (REBELS), using a recent calibration of the [C II]-to-H I conversion factor. We find that the H I gas mass excess in galaxies increases as a function of redshift, with an average of M-HI /M-star approximate to 10, corresponding to H I gas mass fractions of f(HI) = M-HI /(M-star + M-HI) = 90%, at z approximate to 7. Based on the [C II] 158 mu m luminosity function (LF) derived from the same sample of galaxies, we further place constraints on the cosmic H I gas mass density in galaxies (rho(HI)) at this redshift, which we measure to be rho(HI) = 7.1(-3.0)(+6.4) x 10(6) M-circle dot Mpc(-3). This estimate is substantially lower by a factor of approximate to 10 than that inferred from an extrapolation of damped Ly alpha absorber (DLA) measurements and largely depends on the exact [C II] LF adopted. However, we find this decrease in rho(HI) to be consistent with recent simulations and argue that this apparent discrepancy is likely a consequence of the DLA sight lines predominantly probing the substantial fraction of H I gas in high-z galactic halos, whereas [C II] traces the H I in the ISM associated with star formation. We make predictions for this buildup of neutral gas in galaxies as a function of redshift, showing that at z greater than or similar to 5, only approximate to 10% of the cosmic H I gas content is confined in galaxies and associated with the star-forming ISM.

KW - STAR-FORMING GALAXIES

KW - MOLECULAR GAS

KW - INTERSTELLAR-MEDIUM

KW - SCALING RELATIONS

KW - DUST CONTENT

KW - REDSHIFT

KW - EMISSION

KW - EVOLUTION

KW - EPOCH

KW - REIONIZATION

U2 - 10.3847/2041-8213/ac8057

DO - 10.3847/2041-8213/ac8057

M3 - Letter

VL - 934

JO - The Astrophysical Journal Letters

JF - The Astrophysical Journal Letters

SN - 2041-8205

IS - 2

M1 - 27

ER -