REBELS-IFU: Linking damped Lyman-α absorption to [C II] emission and dust content in the Epoch of Reonisation

Neutral gas present in galaxies during the Epoch of Reionisation (EoR) is responsible for regulating star formation, dust growth, and the escape of ionising photons, making it a key ingredient in our understanding of both galaxy assembly and reionisation. However, direct constraints on the H I content of galaxies at z > 6 have been scarce thus far. With JWST, it is possible to obtain a direct probe of this neutral component by surveying Lyα damping wings in galaxy spectra. We analysed JWST/NIRSpec prism spectra of 12 UV-luminous galaxies from the REBELS-IFU program at z ∼ 6.5–7.7, deriving H I column densities by modelling Lyα damping wings. Significant damped Lyα absorption from local H I gas was detected in six galaxies, with N H I ≳ 1021 cm−2. We use the column densities and sizes derived for these sources to estimate their H I masses and compare with L [C II]–M H I calibrations. The resulting H I masses show a tentative correlation with those inferred from [C II], although the [C II]-based estimates are systematically larger, suggesting that the H I reservoirs might extend beyond the [C II]-emitting gas. We also combined measurements taken from damped Lyman-α (Lyα) systems (DLAs) with far-infrared (FIR) derived dust-to-gas ratios (DTGs), dust attenuation, and gas-phase metallicities. No correlation was found between DLA-based and FIR-based DTGs; however, combining the REBELS-IFU sample with literature samples at lower metallicities revealed a strong correlation between A V/N H I and metallicity. These findings suggest that by z ∼ 7 massive galaxies already have the capacity to host substantial, enriched reservoirs of neutral gas and dust, consistent with A V/N H I –metallicity trends at lower redshifts. Finally, we also see tentative evidence of a redshift evolution of the A V/N H I –metallicity relation, with lower A V/N H I at fixed metallicity with increasing redshift, which might point to pristine gas accretion or more efficient dust destruction and/or expulsion.