Di Mascia, F.F.Di MasciaGallerani, S.S.GalleraniBehrens, C.C.BehrensPallottini, A.A.PallottiniCarniani, S.S.CarnianiFerrara, A.A.FerraraBARAI, ParamitaParamitaBARAIVITO, FabioFabioVITOZana, T.T.Zana2025-02-142025-02-1420210035-8711http://hdl.handle.net/20.500.12386/35975We investigate the infrared (IR) emission of high-redshift (z ∼ 6), highly star-forming ( ${{\rm SFR}\gt 100\,{\rm M}_{\odot }\, {\rm yr}^{-1}}$ ) galaxies, with/without active galactic nuclei (AGN), using a suite of cosmological simulations featuring dust radiative transfer. Synthetic spectral energy distributions (SEDs) are used to quantify the relative contribution of stars/AGN to dust heating. In dusty (M<SUB>d</SUB> ≳ 3 × 10<SUP>7</SUP> M<SUB>⊙</SUB>) galaxies, ≳50-90 per cent of the ultraviolet (UV) radiation is obscured by dust inhomogeneities on scales ≳100 pc. In runs with AGN, a clumpy, warm (≈250 K) dust component coexists with a colder (≈60 K) and more diffuse one, heated by stars. Warm dust provides up to ${50 {{\ \rm per\ cent}}}$ of the total infrared (IR) luminosity, but only ${\lesssim}0.1 {{\ \rm per\ cent}}$ of the total mass content. The AGN boosts the MIR flux by 10-100 times with respect to star-forming galaxies, without significantly affecting the far-IR. Our simulations successfully reproduce the observed SED of bright (M<SUB>UV</SUB> ∼ -26) z ∼ 6 quasars, and show that these objects are part of complex, dust-rich merging systems, containing multiple sources (accreting black holes and/or star-forming galaxies) in agreement with recent HST and ALMA observations. Our results show that the proposed ORIGINS missions will be able to investigate the mid-IR (MIR) properties of dusty star-forming galaxies and to obtain good-quality spectra of bright quasars at z ∼ 6. Finally, the MIR-to-FIR flux ratio of faint (M<SUB>UV</SUB> ∼ -24) AGN is >10 times higher than for normal star-forming galaxies. This implies that combined JWST/ORIGINS/ALMA observations will be crucial to identify faint and/or dust-obscured AGN in the distant Universe.STAMPAenArticle10.1093/mnras/stab5282-s2.0-85111195494https://academic.oup.com/mnras/article/503/2/2349/61522672021MNRAS.503.2349DFIS/05 - ASTRONOMIA E ASTROFISICA