Dust in the Early Universe: Dust Formation in the Ejecta of Population III Supernovae

We investigate the formation of dust grains in the ejecta of population IIIsupernovae including pair--instability supernovae, applying a theory of non--steady state nucleation and grain growth. In the calculations, the timeevolution of gas temperature in theejecta, which strongly affects the numberdensity and size of newly formed grains, is calculated by solving the radiativetransfer equation taking account of the energy deposition of radio activeelements. Two extreme cases are considered for the mixing of elements in theejecta; unmixed and uniformly mixed cases within the He--core. The results of calculations are summarized as the followings; in the unmixedejecta, a variety of grain species condense, reflecting the difference of theelemental composition at the formation site in the ejecta, otherwise only oxidegrains condense in the uniformly mixed ejecta. The average size of newly formedgrains spans the range of three orders of magnitude, depending on the grainspecies and the formation condition, and the maximum radius is limited to lessthan 1 $\mu$m, which does not depend on the progenitor mass. The sizedistribution function summed up over all grain species is approximated by apower--law formula whose index is -3.5 for the larger radius and -2.5 for thesmaller one; the radius at the crossover point ranges from 0.004 to 0.1 $\mu$m,depending on the model of supernovae. The fraction of mass locked into dustgrains increases with increasing the progenitor mass; 2--5 % of the progenitormass for core collapse supernovae and 15--30 % for pair--instability supernovaewhose progenitor mass ranges from 140 to 260 $M_{\odot}$. Thus, if the verymassive stars populate the first generation stars, a large amount of dustgrains would be produced in the early universe.Comment: Latex 49 pages including 2 tables and 17 figures; changed content. Accepted for publication in ApJ on Aug. 11, 200