Mancini, M.M.ManciniSCHNEIDER, RAFFAELLARAFFAELLASCHNEIDERGraziani, L.L.GrazianiVALIANTE, ROSAROSAVALIANTEDayal, P.P.DayalMaio, U.U.MaioCiardi, B.B.CiardiHUNT, Leslie KippLeslie KippHUNT2020-04-152020-04-1520150035-8711http://hdl.handle.net/20.500.12386/24036We thank the referee, Hiroyuki Hirashita, for his insightful comments, Laura Pentericci and Daniel Schaerer for their kind clarifications. The research leading to these results has received funding from the European Research Council under the European Union (FP/2007-2013)/ERC Grant Agreement no. 306476. PD acknowledges the support of the Addison Wheeler Fellowship awarded by the Institute of Advanced Study at Durham University. UM has been funded through a Marie Curie fellowship by the European Union (FP/2007-2013), grant agreement no. 267251.We interpret recent ALMA observations of z > 6 normal star-forming galaxies by means of a seminumerical method, which couples the output of a cosmological hydrodynamical simulation with a chemical evolution model which accounts for the contribution to dust enrichment from supernovae, asymptotic giant branch stars and grain growth in the interstellar medium. We find that while stellar sources dominate the dust mass of small galaxies, the higher level of metal enrichment experienced by galaxies with allows efficient grain growth, which provides the dominant contribution to the dust mass. Even assuming maximally efficient supernova dust production, the observed dust mass of the z = 7.5 galaxy A1689-zD1 requires very efficient grain growth. This, in turn, implies that in this galaxy the average density of the cold and dense gas, where grain growth occurs, is comparable to that inferred from observations of quasar (QSO) host galaxies at similar redshifts. Although plausible, the upper limits on the dust continuum emission of galaxies at 6.5 < z < 7.5 show that these conditions must not apply to the bulk of the high-redshift galaxy population.STAMPAenArticle10.1093/mnrasl/slv0702-s2.0-84938926951000361302000015https://academic.oup.com/mnrasl/article/451/1/L70/9559062015MNRAS.451L..70MFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation