Neutrino-dominated accretion flows: second nucleosynthesis factory in core-collapse supernovae and regulation of iron markets in galaxies

Cosmic metals are widely believed to be produced by supernovae (SNe) and compact object mergers. Here, we discuss the nucleosynthesis of neutrino-dominated accretion flows (NDAFs) with outflows in the core-collapse SNe (CCSNe), and show that the outflows from NDAFs can have a significant contribution to the $^{56}$Ni abundance in the faint explosions if the masses of the progenitor stars are within about $25-50$ $M_\odot$. Less massive progenitor stars can produce more $^{56}$Ni than their more massive counterparts in the NDAF outflow nucleosynthesis channel. Therefore, we find that the total (i.e., CCSNe and NDAF outflows) $^{56}$Ni mass per CCSN depends only weakly upon the mass of progenitor stars. In the metallicity evolution, the ratio of $^{56}$Fe (decayed by $^{56}$Ni) mass to the initial total gas mass can increase by $\sim$ 1.95 times if the upper limits of the nucleosynthesis yields from NDAF outflows and CCSNe are considered. Our results might have significant implication for chemical evolution of the the solar neighborhood, galaxies, and active galactic nuclei.