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Title:
The Transition from the First Stars to the Second Stars in the Early Universe
Authors:
Smith, Britton D.; Sigurdsson, Steinn
Affiliation:
AA(Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802; , ), AB(Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802; , )
Publication:
The Astrophysical Journal, Volume 661, Issue 1, pp. L5-L8. (ApJL Homepage)
Publication Date:
05/2007
Origin:
UCP
ApJ Keywords:
Stars: Formation
DOI:
10.1086/518692
Bibliographic Code:
2007ApJ...661L...5S

Abstract

We observe a sharp transition from a singular, high-mass mode of star formation to a low-mass-dominated mode, in numerical simulations, at a metallicity of 10-3 Zsolar. We incorporate a new method for including the radiative cooling from metals into adaptive mesh refinement hydrodynamic simulations. Our results illustrate how metals, produced by the first stars, led to a transition from the high-mass star formation mode of Population III stars to the low-mass mode that dominates today. We ran hydrodynamic simulations with cosmological initial conditions in the standard ΛCDM model, with metallicities, from zero to 10-2 Zsolar, beginning at redshift z=99. The simulations were run until a dense core forms at the center of a 5 × 105 Msolar dark matter halo, at z~18. Analysis of the central 1 Msolar core reveals that the two simulations with the lowest metallicities, Z=0 and 10-4 Zsolar, contain one clump with 99% of the mass, while the two with metallicities Z=10-3 and 10-2 Zsolar each contain two clumps that share most of the mass. The Z=10-3 Zsolar simulation also produced two low-mass protostellar objects with masses between 10-2 and 10-1 Msolar. Gas with Z>=10-3 Zsolar is able to cool to the temperature of the cosmic microwave background (CMB), which sets a lower limit to the minimum fragmentation mass. This suggests that the second-generation stars produced a spectrum of lower mass stars but were still more massive, on average, than stars formed in the local universe.
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