Dust emission from the bulk of galaxies at the Epoch of Reionization

[Abridged] 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 at constraining 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 galaxies covered by the A3COSMOS database and used the measurements as constraints to perform UV-to-FIR SED modelling. We obtain tentative signals for the brightest UV galaxies (MUV<-19mag) as well as for the most massive ones (log Mstar>9) at 6<z<7, and upper limits for fainter (MUV>-19mag), lower mass sources (log Mstar<9), and at higher redshift (z>7). Fitting these 6<z<7 galaxies with ALMA constraints results in lower star formation rates (-0.4dex) and FUV attenuation (-0.5mag) for galaxies with log Mstar>8, compared to the fit without FIR. We extend the LIR vs MUV relation down to MUV=-19mag and show a tentative breakdown of the relation at fainter UV magnitudes. The positions of the JADES z~6.5 sample on the IRX versus beta and IRX versus Mstar diagrams are consistent with those 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 these UV-selected galaxies. Extending our analysis of the infrared properties to z>7 galaxies, we find a non-evolution of beta with redshift in the MUV range probed by our sample (-17.24+/-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 1/sSFR 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.