Extremely-Metal Poor Stars in the Milky Way: A Second Generation Formed after Reionization

Abstract

Cosmological simulations of Population III star formation suggest an initial mass function (IMF) biased toward very massive stars (M>100Msun) formed in minihalos at redshift z>20, when the cooling is driven by molecular hydrogen. However, this result conflicts with observations of extremely-metal poor (EMP) stars in the Milky Way halo, whose r-process elemental abundances appear to be incompatible with those expected from very massive Population III progenitors. We propose a new solution to the problem in which the IMF of second-generation stars formed at z>10, before reionization, is deficient in sub-solar mass stars, owing to the high cosmic microwave background temperature floor. The observed EMP stars are formed preferentially at z<10 in pockets of gas enriched to metallicity Z>10^{-3.5} Zsun by winds from Population II stars. Our cosmological simulations of dark matter halos like the Milky Way show that current samples of EMP stars can only constrain the IMF of late-time Population III stars, formed at z<13 in halos with virial temperature Tvir~10^4 K. This suggests that pair instability supernovae were not produced primarily by this population. To begin probing the IMF of Population III stars formed at higher redshift will require a large survey, with at least 500 and probably several thousand EMP stars of metallicities Z~10^{-3.5} Zsun.

ApJ accepted, simulations of MW-like halos added, conclusions unchanged

References in corpus (17)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• Supernova 2007bi as a pair-instability explosion
• Fragmentation of star-forming clouds enriched with the first dust
• Population III star formation in a Lambda CDM universe, I: The effect of formation redshift and environment on protostellar accretion rate
• Population III star formation in a Lambda CDM universe, II: Effects of a photodissociating background
• Probing the Formation of the First Low-Mass Stars with Stellar Archaeology
• Chemical Evolution in Hierarchical Models of Cosmic Structure II: The Formation of the Milky Way Stellar Halo and the Distribution of the Oldest Stars
• The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
• Two populations of metal-free stars in the early Universe
• Uncovering the Chemical Signature of the First Stars in the Universe
• Metal-Free Gas Supply at the Edge of Reionization: Late-Epoch Population III Star Formation
• The First Stars in The Universe
• The minimum stellar metallicity observable in the Galaxy
• Carbon-Enhanced Metal-Poor Stars, the Cosmic Microwave Background, and the Stellar IMF in the Early Universe
• Distribution of the very first PopIII stars and their relation to bright z~6 quasars
• Where can we really find the First Stars' Remnants today?

Cited by in corpus (13)

• The Birth of a Galaxy: Primordial Metal Enrichment and Stellar Populations
• The spectral evolution of the first galaxies. I. James Webb Space Telescope detection limits and color criteria for population III galaxies
• The relative and absolute ages of old globular clusters in the LCDM framework
• Compact Stellar Binary Assembly in the First Nuclear Star Clusters and r-Process Synthesis in the Early Universe
• Following the Cosmic Evolution of Pristine Gas II: The search for Pop III-Bright Galaxies
• The first galaxies: simulating their feedback-regulated assembly
• Following The Cosmic Evolution Of Pristine Gas I: Implications For Milky Way Halo Stars
• Formation History of Metal-Poor Halo Stars with Hierarchical Model and the Effect of ISM accretion on the Most Metal-Poor Stars
• Modelling the chemical evolution of the Galaxy halo
• PopIII signatures in the spectra of PopII/I GRBs
• The clustering properties of the first galaxies
• Simulating extremely metal-poor gas and DLA metal content at redshift z=7
• Semi analytical description of formation of galaxies and clusters of galaxies