2010ApJ...717..542K -
Astrophys. J., 717, 542-561 (2010/July-1)
Formation history of metal-poor halo stars with the hierarchical model and the effect of interstellar matter accretion on the most metal-poor stars.
KOMIYA Y., HABE A., SUDA T. and FUJIMOTO M.Y.
Abstract (from CDS):
We investigate star formation and chemical evolution in the early universe by considering the merging history of the Galaxy in the Λ cold dark matter scenario according to the extended Press-Schechter theory. We give some possible constraints from comparisons with observation of extremely metal-poor (EMP) stars, made available by the recent large-scale surveys and by the follow-up high-resolution spectroscopy. We demonstrate that (1) the hierarchical structure formation can explain the characteristics of the observed metallicity distribution function including a break around [Fe/H] = -4; (2) a high-mass initial mass function (IMF) of peak mass ∼10 M☉ with the contribution of binaries, derived from the statistics of carbon-enhanced EMP stars, predicts the frequency of low-mass survivors consistent with the number of EMP stars observed for -4 ≲ [Fe/H] ≲ -2.5; (3) the stars formed from primordial gas before the first supernova (SN) explosions in their host mini-halos are assigned to the hyper metal-poor (HMP) stars with [Fe/H] ∼ -5; and (4) there is no indication of significant changes in the IMF and the binary contribution at metallicities -4 ≳ [Fe/H] ≳ -2.5, or even larger, as far as the field stars of the Galactic halo are concerned. We further study the effects of surface pollution through the accretion of interstellar matter (ISM) along the chemical and dynamical evolution of the Galaxy for low-mass Population III and EMP survivors. Because of the shallower potential of smaller halos, the accretion of ISM in the mini-halos in which these stars were born dominates the surface metal pollution. This can account for the surface iron abundances as observed for the HMP stars if the cooling and concentration of gas in their birth mini-halos are taken into account. We also study the feedback effect from the very massive Population III stars. The metal pre-pollution by pair-instability SNe is shown to be compatible with the observed lack of their nucleosynthetic signatures when some positive feedback on gas cooling works and changes the IMF from being very massive to being high mass.
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Journal keyword(s):
Galaxy: evolution - Galaxy: formation - stars: abundances - stars: Population II
Simbad objects:
4
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