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    Probing Pre-Galactic Metal Enrichment With High-Redshift Gamma-Ray Bursts

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    Date
    2012-11
    Author
    Wang, F. Y.
    Bromm, Volker
    Greif, Thomas H.
    Stacy, Athena
    Dai, Z. G.
    Loeb, Abraham
    Cheng, K. S.
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    Abstract
    We explore high-redshift gamma-ray bursts (GRBs) as promising tools to probe pre-galactic metal enrichment. We utilize the bright afterglow of a Population III (Pop III) GRB exploding in a primordial dwarf galaxy as a luminous background source, and calculate the strength of metal absorption lines that are imprinted by the first heavy elements in the intergalactic medium (IGM). To derive the GRB absorption line diagnostics, we use an existing highly resolved simulation of the formation of a first galaxy which is characterized by the onset of atomic hydrogen cooling in a halo with virial temperature greater than or similar to 10(4) K. We explore the unusual circumburst environment inside the systems that hosted Pop III stars, modeling the density evolution with the self-similar solution for a champagne flow. For minihalos close to the cooling threshold, the circumburst density is roughly proportional to (1 + z) with values of about a few cm(-3). In more massive halos, corresponding to the first galaxies, the density may be larger, n greater than or similar to 100 cm(-3). The resulting afterglow fluxes are weakly dependent on redshift at a fixed observed time, and may be detectable with the James Webb Space Telescope and Very Large Array in the near-IR and radio wavebands, respectively, out to redshift z greater than or similar to 20. We predict that the maximum of the afterglow emission shifts from near-IR to millimeter bands with peak fluxes from mJy to Jy at different observed times. The metal absorption line signature is expected to be detectable in the near future. GRBs are ideal tools for probing the metal enrichment in the early IGM, due to their high luminosities and featureless power-law spectra. The metals in the first galaxies produced by the first supernova (SN) explosions are likely to reside in low-ionization stages (C II, OI, Si II and Fe II). We show that, if the afterglow can be observed sufficiently early, analysis of the metal lines may distinguish whether the first heavy elements were produced in a pair-instability supernova or a core-collapse (Type II) SN, thus constraining the initial mass function of the first stars.
    Department
    Astronomy
    Subject
    cosmology: observations
    cosmology: theory
    galaxies: high-redshift
    gamma-ray burst: general
    quasars: absorption lines
    initial mass function
    population-iii stars
    atomic-absorption lines
    1st stars
    intergalactic medium
    primordial gas
    early universe
    light
    curves
    hii-regions
    protostellar feedback
    astronomy & astrophysics
    URI
    http://hdl.handle.net/2152/34728
    Citation
    Wang, F. Y., Volker Bromm, Thomas H. Greif, Athena Stacy, Z. G. Dai, Abraham Loeb, and K. S. Cheng. "Probing pre-galactic metal enrichment with high-redshift gamma-ray bursts." The Astrophysical Journal, Vol. 760, No. 1 (Nov., 2012): 27.
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