Dust emission from the bulk of galaxies in the Epoch of Reionisation

The excess of UV-bright galaxies observed at z > 10 has been one of the major surprises of the early JWST observations. Several explanations have been proposed to understand the mild change in space density of the UV-bright galaxies at these high redshifts, among them an evolution of dust attenuation properties in galaxies. However, our view of dust in primordial galaxies is limited towards a few tens of z ∼ 7 galaxies, pre-selected from UV-optical observations, and are thus not necessarily representative of the bulk of the sources at these redshifts. In this work, we aim to constrain the dust properties of galaxies at 6 < z < 12 by making the most of the A3COSMOS database in the JADES/GOODS-South field. We stacked ALMA band 6 and 7 observations of 4464 JADES galaxies covered by the A3COSMOS database and used the measurements as constraints to perform UV-to-FIR SED modelling. We obtained tentative signals for the brightest UV galaxies (MUV < −19 mag) as well as for the most massive ones (logM⋆/M⊙ > 9) at 6 < z < 7, and upper limits for fainter (MUV > −19 mag), lower-mass sources (logM⋆/M⊙ < 9), or ones at higher redshift (z > 7). Fitting these 6 < z < 7 galaxies with ALMA constraints results in lower star formation rates (−0.4 dex) and FUV attenuation (−0.5 mag) for galaxies with logM⋆/M⊙ > 8, compared to the fit without FIR. We extend the LIR vs MUV relation down to MUV = −19 mag and show a tentative breakdown of the relation at fainter UV magnitudes. The positions of the JADES z ∼ 6.5 sample on the infrared excess (IRX) versus β and IRX versus M⋆ diagrams are consistent with the ones of the ALPINE (z ∼ 5.5) and REBELS (z ∼ 6.5) samples, suggesting that the dust composition and content of our mass-selected sample are similar to the ones of these UV-selected galaxies. Extending our analysis of the infrared properties to z > 7 galaxies, we find a non-evolution of β in the MUV range probed by our sample (–17.24$ ^{+0.54}_{-0.62} $), and highlight the fact that samples from the literature are not representative of the bulk of galaxy populations at z > 6. We confirm a linear relation between AV and sSFR−1 with a flatter slope than previously reported due to the use of ALMA constraints. Our results suggest that rapid and significant dust production has already happened by z ∼ 7.