• DOI:10.3847/2041-8213/ac8057
• Corpus ID: 249712594

The ALMA REBELS Survey: The Cosmic H i Gas Mass Density in Galaxies at z ≈ 7

@article{Heintz2022TheAR,
  title={The ALMA REBELS Survey: The Cosmic H i Gas Mass Density in Galaxies at z ≈ 7},
  author={Kasper E. Heintz and Pascal A. Oesch and Manuel Aravena and Richard Bouwens and Pratika Dayal and A. Ferrara and Yoshinobu Fudamoto and Luca Graziani and Hanae Inami and Laura Sommovigo and Renske Smit and Mauro Stefanon and Michael W. Topping and Andrea Pallottini and Paul P. van der Werf},
  journal={The Astrophysical Journal Letters},
  year={2022},
  volume={934}
}

• K. E. Heintz, P. Oesch, +12 authors P. P. van der Werf
• Published 15 June 2022
• Physics
• The Astrophysical Journal Letters

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 ∼ 6.5–7.8 surveyed for [C ii] 158 μm 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 ⋆ ≈ 10, corresponding to H i gas mass fractions of f Hi = M Hi /(M ⋆ + M Hi ) = 90%, at z ≈ 7. Based on the [C ii] 158 μm luminosity function (LF) derived from the same sample of galaxies, we further place constraints on the cosmic H i gas mass density in galaxies (ρ Hi ) at this redshift, which we measure to be ρHI=7.1−3.0+6.4×106M⊙Mpc−3 . This estimate is substantially lower by a factor of ≈10 than that inferred from an extrapolation of damped Lyα absorber (DLA) measurements and largely depends on the exact [C ii] LF adopted. However, we find this decrease in ρ 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 ≳ 5, only ≈10% of the cosmic H i gas content is confined in galaxies and associated with the star-forming ISM.