UPPER BOUND ON THE FIRST STAR FORMATION HISTORY
- Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics, Stanford University and SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States)
- Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)
Our understanding of the nature of the extragalactic background light (EBL) has improved with the recent development of gamma-ray observation techniques. An open subject in the context of the EBL is the reionization epoch, which is an important probe of the formation history of first stars, the so-called Population III (Pop III) stars. Although the mechanisms for the formation of Pop III stars are rather well understood on theoretical grounds, their formation history is still veiled in mystery because of their faintness. To shed light on this matter, we study jointly the gamma-ray opacity of distant objects and the reionization constraints from studies of intergalactic gas. By combining these studies, we obtain a sensitive upper bound on the Pop III star formation rate density of ρ-dot {sub ∗}(z)<0.01[(1+z)/(1+7.0)]{sup 3.4}(f{sub esc}/0.2){sup −1}(C/3.0) M{sub ⊙} yr{sup −1} Mpc{sup −3} at z ≥ 7, where f {sub esc} and C are the escape fraction of ionizing photons from galaxies and the clumping factor of the intergalactic hydrogen gas. This limit is a ∼10 times tighter constraint compared with previous studies that take into account gamma-ray opacity constraints only. Even if we do not include the current gamma-ray constraints, the results do not change. This is because the detected gamma-ray sources are still at z ≤ 4.35 where the reionization has already finished.
- OSTI ID:
- 22364011
- Journal Information:
- Astrophysical Journal Letters, Vol. 781, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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