Following the Cosmic Evolution of Pristine Gas. I. Implications for Milky Way Halo Stars

Abstract

We make use of a new subgrid model of turbulent mixing to accurately follow the cosmological evolution of the first stars, the mixing of their supernova (SN) ejecta, and the impact on the chemical composition of the Galactic Halo. Using the cosmological adaptive mesh refinement code ramses, we implement a model for the pollution of pristine gas as described in Pan et al. Tracking the metallicity of Pop III stars with metallicities below a critical value allows us to account for the fraction of Z < Z crit stars formed even in regions in which the gas's average metallicity is well above Z crit . We demonstrate that such partially-mixed regions account for 0.5 to 0.7 of all Pop III stars formed up to z = 5. Additionally, we track the creation and transport of "primordial metals" (PM) generated by Pop III SNe. These neutron-capture deficient metals are taken up by second-generation stars and likely lead to unique abundance signatures characteristic of carbon-enhanced, metal-poor (CEMP-no) stars. As an illustrative example, we associate primordial metals with abundance ratios used by Keller et al.

Origin of the CEMP-no Group Morphology in the Milky Way

“…III and Pop. II stars (e.g., Salvadori et al 2015;de Bennassuti et al 2017;Sarmento et al 2017;Chiaki et al 2018;Sarmento et al 2019).…”

Dynamic localized turbulent diffusion and its impact on the galactic ecosystem

“…In addition to cooling, the redistribution of metals can impact other processes, such as the sites and formation history of the putative Population III (Pop III) stars and supermassive black holes (SMBHs). Pop III stars are associated with star formation involving near-pristine gas with an upper limit on metallicities somewhere in the range [Z] ∼ −6 to [Z] ∼ −3 (Sarmento et al 2016). As for SMBHs, a number of authors (e.g.…”

On Neutron Star Mergers as the Source of r-process-enhanced Metal-poor Stars in the Milky Way

“…We start by showing the overall star formation history of our MW type galaxy and its corresponding metallicity (Xu et al 2016), as well as simulations by Sarmento et al (2017), Barai & de Gouveia Dal Pino (2018), and Johnson et al (2012). We also include observations by Madau & Dickinson (2014) and a LF-based SFRD by Finkelstein (2016).…”

“…III stars, and the pristine gas mass fraction, P , which models the fraction of unpolluted gas within each simulation cell with Z < Z crit . We briefly describe these scalars here, and a more thorough discussion is presented in Sarmento et al (2017).…”

“…III stars by following the evolution of pristine gas in each simulation cell with a subgrid model of turbulent mixing that is crucial for properly identifying Pop. III stars whose ejecta are the precursor to the formation of CEMP stars (Sarmento et al 2017;Naiman et al 2018); (iii) Adopting a high dark matter particle mass resolution in order to resolve halos where the MP and CEMP stars form in the early universe.…”