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The First Stars and Galaxies: Challenges for the Next Decade Participants
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Title: Molecules and Dust in the Early Universe: the Supernova Connection Author(s): Isabelle Cherchneff Abstract: We present new results on the formation of molecules and dust in the ejecta of Pop III supernovae. A chemical kinetic approach is used to describe the synthesis of molecules and the nucleation of small solid clusters. All relevant chemical processes are included as well as non-thermal processes such as destruction of molecules by Compton electrons and dissociation by ultraviolet radiation. The chemistry is applied to the ejecta of massive pair-instabilty (PISN) and low-mass core-collapse (CCSN) supernovae of zero-metallicity progenitors. Fully-microscopically mixed and unmixed ejecta are considered. We show that molecule formation is effective in all ejecta. In particular, for unmixed ejecta, a 170 Msun PISN forms ~ 37 Msun of molecules in its ejecta whereas the molecular phase represents ~ 1.2 Msun for a 20 Msun CCSN. The dominant species surviving dust nucleation in both cases are O2, SiS and CO. At high redshift, PISNe therefore eject ~ 45 % of their progenitor mass in the form of molecules to the local, pristine gas. The unmixed ejecta of a 170 Msun progenitor supernova synthesizes ~ 5.8 Msun of small dust clusters, while its 20 Msun counterpart produces ~ 0.077 Msun. Our results point to smaller amounts of dust formed in the ejecta by a factor ~ 5 compared to values derived by previous studies, and to a different chemical composition for the dust. Such deviations result from some erroneous assumptions, the inappropriate use of classical nucleation theory to model dust formation, and the omission of the synthethis of molecules in supernova ejecta. We also find that the unmixed ejecta of massive Pop III supernovae chiefly form silica and/or silicates and pure silicon grains whereas their lower mass counterparts form a dust mixture dominated by silica and/or silicates, pure silicon and iron sulphides. Amorphous carbon only condenses in low-mass progenitors via the nucleation of carbon chains and rings characteristic of the synthesis of fullerenes when their carbon-rich zone is deprived of He+. The first dust enrichment to the primordial gas in the early universe from Pop III massive supernova comprises primarily pure silicon, silica and silicates. If carbon dust is present at z > 6, alternative dust sources must be considered.
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