GB3 - Cosmology from GRBs |
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Speaker |
Wu, Xuefeng |
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Coauthors |
Junjie Wei |
| Talk Title |
Gamma-Ray Burst Cosmology: Hubble Diagram and Star Formation History |
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Abstract |
We will introduce the disadvantages for Type Ia supernovae (SNe Ia) as standard candles to measure the Universe, and suggest Gamma-ray bursts (GRBs) can be used as a powerful tool for investigating the high redshift Universe. We firstly use GRBs as standard candles in constructing the Hubble diagram at redshifts beyond the current reach of SNe Ia observations. Then we measure high-z star formation rate (SFR) using GRBs. We confirm that the latest Swift sample of GRBs reveals an increasing evolution in the GRB rate relative to SFR at high redshifts. The observed discrepancy between the GRB rate and the SFR may be eliminated by assuming a cosmic evolution in metallicity. Assuming that the SFR and GRB rate are related via an evolving metallicity, we find that the GRB data constrain the slope of the high-z SFR to be $-2.41_{-2.09}^{+1.87}$. In addition, first stars can only form in structures that are suitably dense, which can be parameterized by the minimum dark matter halo mass M_min. M_min must play an important role in star formation. We can constrain M_min<10^12.5 M_sun at 68% confidence level from the GRB data. |
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