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

¹ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
² Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
³ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁴ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06000 Nice, France
⁵ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
⁶ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁷ Max-Planck-Institut für Extraterrestische Physik (MPE), Giessenbachstr., 85748 Garching, Germany
⁸ Purple Mountain Observatory, Chinese Academy of Sciences, 10 Yuanhua Road, Nanjing, 210023 PR, China

^⋆ Corresponding author: laure.ciesla@lam.fr

Received: 3 December 2024
Accepted: 14 July 2025

Abstract

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 (M_UV <  −19 mag) as well as for the most massive ones (logM_⋆/M_⊙ >  9) at 6 <  z <  7, and upper limits for fainter (M_UV >  −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 L_IR vs M_UV relation down to M_UV = −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 M_UV range probed by our sample (–17.24_−0.62^+0.54), 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 A_V 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.