Astrophys. J., 735, 2 (2011/July-1)
Exploring dust extinction at the edge of reionization.
ZAFAR T., WATSON D.J., TANVIR N.R., FYNBO J.P.U., STARLING R.L.C. and LEVAN A.J.
Abstract (from CDS):
The brightness of gamma-ray burst (GRB) afterglows and their occurrence in young, blue galaxies make them excellent probes to study star-forming regions in the distant universe. We here elucidate dust extinction properties in the early universe through the analysis of the afterglows of all known z > 6 GRBs: GRB 090423, 080913, and 050904, at z = 8.2, 6.69, and 6.295, respectively. We gather all available optical and near-infrared photometry, spectroscopy, and X-ray data to construct spectral energy distributions (SEDs) at multiple epochs. We then fit the SEDs at all epochs with a dust-attenuated power law or broken power law. We find no evidence for dust extinction in GRB 050904 and GRB 090423, with possible evidence for a low level of extinction in GRB 080913. We compare the high redshift GRBs to a sample of lower redshift GRB extinctions and find a lack of even moderately extinguished events (AV ∼ 0.3) above z ≳ 4. In spite of the biased selection and small number statistics, this result hints at a decrease in dust content in star-forming environments at high redshifts.
dark ages, reionization, first stars - dust, extinction - galaxies: high-redshift - gamma-ray burst: individual (GRB 090423, GRB 080913, GRB 050904)
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