How the First Stars Regulated Star Formation. II. Enrichment by Nearby Supernovae

Abstract

Metals from Population III (Pop III) supernovae led to the formation of less massive Pop II stars in the early universe, altering the course of evolution of primeval galaxies and cosmological reionization. There are a variety of scenarios in which heavy elements from the first supernovae were taken up into second-generation stars, but cosmological simulations only model them on the largest scales. We present small-scale, high-resolution simulations of the chemical enrichment of a primordial halo by a nearby supernova after partial evaporation by the progenitor star. We find that ejecta from the explosion crash into and mix violently with ablative flows driven off the halo by the star, creating dense, enriched clumps capable of collapsing into Pop II stars. Metals may mix less efficiently with the partially exposed core of the halo, so it might form either Pop III or Pop II stars. Both Pop II and III stars may thus form after the collision if the ejecta do not strip all the gas from the halo. The partial evaporation of the halo prior to the explosion is crucial to its later enrichment by the supernova.

Predicting the locations of possible long-lived low-mass first stars: importance of satellite dwarf galaxies

“…These newly-enriched regions are the birthplaces of the second generation, Population II or Pop II stars. Haloes that are enriched from the outside accumulate metals in dense clumps and form Pop II stars (Smith et al 2015;Chen et al 2017). Without properly simulating the mixing process, the exact metallicity of these clumps is difficult to estimate.…”

Implications of inhomogeneous metal mixing for stellar archaeology

“…One process is shielding. Metal-rich winds cannot penetrate dense gas clumps easily (Jeon et al 2014;Chen et al 2017;Chiaki et al 2018). If gas cooling and clump formation occur earlier than metal enrichment, the metallicity shift may take a negative value.…”

Chemical enrichment of Pop III supernovae in the first galaxies

“…Based on the highly-resolved simulations of Chen et al (2017), we conclude the external enrichment only work for very massive Pop III stars of 200 -250 M , which have strong radiative feedback and die as powerful pair-instability supernovae (Chen et al (2014)) to break out the dense shell of the nearby halo and mix metal deep into the center to initialize the Pop II star formation. Therefore, the external enrichment channel can be promising only if the Pop III IMF is very top-heavy.…”

“…collide into the photo-heated halo and drive mixing at the outer shell of the halo. From five out of six models in Chen et al (2017), most of the halos seem to be able to prevent from the enrichment of SN metals. If it were true for the real situation, the Pop III stars might have still formed in these nearby halos.…”

“…We discuss the results of an external enrichment scenario based on Chen et al (2017), that investigated how the first supernovae regulated the star formation in the nearby halos. Before the incoming metal, the pre-enriched minihalo is first photo-evaporation by the Pop III radiative feedback and the inputs of ionizing photons of hydrogen/helium are from the one-dimensional stellar evolution model.…”