Statistics – Applications
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...204.3403t&link_type=abstract
American Astronomical Society Meeting 204, #34.03; Bulletin of the American Astronomical Society, Vol. 36, p.703
Statistics
Applications
Scientific paper
I will critique the hypothesis that the first stars were very massive stars (VMS; M > 140 M&sun;) by reviewing the two major lines of evidence for the existence of VMS: (1) that the relative metal abundances of extremely metal-poor Galactic halo stars show evidence of VMS enrichment, and (2) that the high electron-scattering optical depth (τ e) to the CMB found by WMAP requires VMS for reionization in a concordance Λ CDM cosmology. Enrichment by Type II supernovae and/or ``hypernovae'' from zero-metallicity progenitors with M = 8 - 40 M&sun; can explain the observed trends nucleosynthetic trends better than VMS exploding as pair-instability SN. I use the nucleosynthesis results and stellar evolution models to construct an initial mass function (IMF) for reionization. Because the lifetime-integrated ionizing photon efficiency of metal-free stars peaks at ˜ 120 M&sun; and declines at higher mass, an IMF with an approximate lower bound at M ˜ 10 - 20 M&sun; and no VMS can maximize the ionizing photon budget and still be consistent with the nucleosynthetic evidence. Semi-analytic reionization models for H I and He II reionization demonstrate that such an IMF can reproduce τ e ≃ 0.10 - 0.14, consistent with the range from WMAP, without extreme astrophysical assumptions. I conclude, on the basis of these results, that VMS are not necessary to meet the existing constraints commonly taken to motivate them. I will also present recent FUSE observations of the He II Gunn-Peterson effect seen z 3, and I will discuss how future applications of this technique can further constrain the nature of the first stars and quasars.
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