Abundance anomalies in metal-poor stars from Population III supernova ejecta hydrodynamics

Abstract

We present a simulation of the long-term evolution of a Population III supernova remnant in a cosmological minihalo. Employing passive Lagrangian tracer particles, we investigate how chemical stratification and anisotropy in the explosion can affect the abundances of the first low-mass, metal-enriched stars. We find that reverse shock heating can leave the inner mass shells at entropies too high to cool, leading to carbon-enhancement in the re-collapsing gas. This hydrodynamic selection effect could explain the observed incidence of carbonenhanced metal-poor (CEMP) stars at low metallicity. We further explore how anisotropic ejecta distributions, recently seen in direct numerical simulations of core-collapse explosions, may translate to abundances in metal-poor stars. We find that some of the observed scatter in the Population II abundance ratios can be explained by an incomplete mixing of supernova ejecta, even in the case of only one contributing enrichment event. We demonstrate that the customary hypothesis of fully-mixed ejecta clearly fails if post-explosion hydrodynamics prefers the recycling of some nucleosynthetic products over others. Furthermore, to fully exploit the stellar-archaeological program of constraining the Pop III initial mass function from the observed Pop II abundances, considering these hydrodynamical transport effects is crucial. We discuss applications to the rich chemical structure of ultra-faint dwarf satellite galaxies, to be probed in unprecedented detail with upcoming spectroscopic surveys.

Towardsab initioextremely metal-poor stars

“…The orbital extent could be related to the half-light radii of the ultra faint dwarf (UFD) galaxies. The simulation substantially improves upon the idealized precursor simulations we reported in Ritter et al (2012) and Sluder et al (2016). It is the logical next step toward providing an end-to-end proof-of-concept for extremely metal poor star formation in the first metal-enriched cosmic objects.…”

“…The heavier elements (e.g., the iron group) that fall back onto the remnant in spherically-symmetric models are instead ejected in jets (Wongwathanarat, Müller & Janka 2015). Intrinsic explosion anisotropy may imply some irreducible scatter in the heavier element abundances in enriched gas, even for similar mass supernova progenitors (Sluder et al 2016).…”

“…At the other end of the range of possibilities, the typical single Pop III could disperse its metals so compactly, with minimum dilution, as to immediately produce stars much more metal rich than the observed extremely metal poor stars. Thanks to its complexity, the recycling of Pop III ejecta into the first metal-enriched stars remains an active research area (e.g., Whalen et al 2008;Ritter et al 2012Ritter et al , 2015Cooke & Madau 2014;Jeon et al 2014;Sluder et al 2016).…”

Low-energy Population III supernovae and the origin of extremely metal-poor stars

“…Mixing on small scales in the explosion must also be understood to predict the metallicities of the stars that form in the debris of the SN because it sets the initial conditions for mixing, cooling and collapse of gas on larger scales in the intergalactic medium (IGM). Mixing in Pop III CC and PI SNe has previously been studied by Joggerst et al (2009);Joggerst & Whalen (2011);Chen et al (2011Chen et al ( , 2014 and on larger, cosmological scales by Wise & Abel (2008); Greif et al (2010); Jeon et al (2014); Chiaki et al (2015); Chen et al (2015); Ritter et al (2015); Sluder et al (2015).…”

Carbon abundances of reference late-type stars from 1D analysis of atomic C i and molecular CH lines

“…The situation with understanding sources of the carbon production in the early Galaxy is complicated by a discovery of the Carbon-Enhanced Metal-Poor (CEMP) stars that show very high enhancements in carbon, with [C/Fe] up to 3 dex (see recent papers of Behara et al 2010, Spite et al 2013, Ito et al 2013, Lee et al 2013, Cohen et al 2013, Otsuka & Tajitsu 2013, Kennedy et al 2014, Abate et al 2015, Ramirez-Ruiz et al 2015, Aoki et al 2015, Sluder et al 2015. It is still debated whether their carbon enhancements are inborn, or their atmospheres were polluted, most likely by accretion from an AGB binary companion.…”