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 gsim 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.
|Number of pages||6|
|Journal||The Astrophysical Journal: an international review of astronomy and astronomical physics|
|Publication status||Published - 1 Jul 2011|
- dark ages, reionization, first stars
- dust, extinction
- galaxies: high-redshift
- gamma-ray burst: individual: (GRB 090423, 080913, and 050904(