The Chemistry of Population Iii Supernova Ejecta. Ii. The Nucleation of Molecular Clusters as a Diagnostic for Dust in the Early Universe

Abstract

We study the formation of molecular precursors to dust in the ejecta of Population III supernovae using a chemical kinetic approach to follow the evolution of small dust cluster abundances from day 100 to day 1000 after explosion. Our work focuses on zero-metallicity 20 M ⊙ and 170 M ⊙ progenitors, and we consider fully-macroscopically mixed and unmixed ejecta. The dust precursors comprise molecular chains, rings and small clusters of chemical composition relevant to the initial elemental composition of the ejecta under study. The nucleation stage for small silica, metal oxides and sulphides, pure metal, and carbon clusters is described with a new chemical reaction network highly relevant to the kinetic description of dust formation in hot circumstellar environments. We consider the effect of the pressure dependence of critical nucleation rates, and test the impact of microscopically-mixed He + on carbon dust formation. Two cases of metal depletion on silica clusters (full and no depletion) are considered to derive upper limits to the amounts of dust produced in SN ejecta at 1000 days, while the chemical composition of clusters gives a prescription for the type of dust formed in Pop. III supernovae.We show that the cluster mass produced in the fully-mixed ejecta of a 170M ⊙ progenitor is ∼ 25 M ⊙ whereas its 20 M ⊙ counterpart forms ∼ 0.16 M ⊙ of clusters. The unmixed ejecta of a 170 M ⊙ progenitor supernova synthesizes ∼ 5.6 M ⊙ of small clusters, while its 20 M ⊙ counterpart produces ∼ 0.103 M ⊙ . Our results point to smaller amounts of dust formed in the ejecta of Pop. III supernovae by a factor ∼ 5 compared to values derived by previous studies, and to different dust chemical composition. Such deviations result from some erroneous assumptions made, 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 can only condense in ejecta where the carbon-rich zone is deprived of He + via the nucleation of carbon chains and rings characteristic of the synthesis of fullerenes. 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 redshift z > 6, alternative dust sources must be considered.

Dust formation in the oxygen-rich AGB star IK Tauri

“…The chemical networks of Duari et al (1999) and Cherchneff (2006) have been revised and extended to include the processes involved in the formation of clusters (see below and Sarangi & Cherchneff 2013. Reaction rates were taken primarily from the National Institute of Standards and Technology Chemical Kinetics Database, the 2012 version of the UMIST Database for Astrochemistry (McElroy et al 2013), specific studies of ceramic production in flames (e.g., Zachariah & Tsang 1995) and modelling of other circumstellar environments (Cherchneff & Dwek 2009Sarangi & Cherchneff 2013).…”

Dust production 680–850 million years after the Big Bang

“…Theoretical models predict that a SN can produce at most ∼1.3 M of dust (Todini & Ferrara 2001;Nozawa et al 2003), but likely only < ∼ 0.1 M survives the associated shocks and is released into the ISM (Bianchi & Schneider 2007;Cherchneff & Dwek 2010;Gall et al 2011a;Lakićević et al 2015). Large amounts of dust have been found in the Scottish Universities Physics Alliance.…”

Dust grain growth in the interstellar medium of 5 < z < 6.5 quasars

“…However, for the case of SN dust, only 0.1 M of the dust actually survives in the associated shocks (Bianchi & Schneider 2007;Cherchneff & Dwek 2010).…”