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Future Constraints on the Reionization History and the Ionizing Sources from Gamma-Ray Burst Afterglows

Lidz, Adam and Chang, Tzu-Ching and Mas-Ribas, Lluís and Sun, Guochao (2021) Future Constraints on the Reionization History and the Ionizing Sources from Gamma-Ray Burst Afterglows. Astrophysical Journal, 917 (2). Art. No. 58. ISSN 0004-637X. doi:10.3847/1538-4357/ac0af0.

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We forecast the reionization history constraints, inferred from Lyα damping wing absorption features, for a future sample of ∼20 z ≥ 6 gamma-ray burst (GRB) afterglows. We describe each afterglow spectrum by a three-parameter model. First, L characterizes the size of the ionized region (the "bubble size") around a GRB host halo. Second, 〈x_(H i)〉 is the volume-averaged neutral fraction outside of the ionized bubble around the GRB, which is approximated as spatially uniform. Finally, NH i denotes the column density of a local damped Lyα absorber (DLA) associated with the GRB host galaxy. The size distribution of ionized regions is extracted from a numerical simulation of reionization and evolves strongly across the epoch of reionization (EoR). The model DLA column densities follow the empirical distribution determined from current GRB afterglow spectra. We use a Fisher matrix formalism to forecast the 〈x_(H i)(z)〉 constraints that can be obtained from follow-up spectroscopy of afterglows with S/N = 20 per R = 3000 resolution element at the continuum. We find that the neutral fraction may be determined to better than 10%–15% (1σ) accuracy from this data across multiple independent redshift bins at z ∼ 6–10, spanning much of the EoR, although the precision degrades somewhat near the end of reionization. A more futuristic survey with 80 GRB afterglows at z ≥ 6 can improve the precision here by a factor of 2 and extend measurements out to z ∼ 14. We further discuss how these constraints may be combined with estimates of the escape fraction of ionizing photons derived from the DLA column density distribution toward GRBs extracted at slightly lower redshift, z ∼ 5. This combination will help in testing whether we have an accurate census of the sources that reionized the universe.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lidz, Adam0000-0002-3950-9598
Chang, Tzu-Ching0000-0001-5929-4187
Mas-Ribas, Lluís0000-0003-4584-8841
Sun, Guochao0000-0003-4070-497X
Additional Information:© 2021. The American Astronomical Society. Received 2021 May 5; revised 2021 June 9; accepted 2021 June 11; published 2021 August 17. We thank Matt McQuinn for providing the simulation outputs used in computing the ionized skewer size distributions in Figure 3. We thank the Gamow Explorer team for inspiring this work and for useful discussions, especially with Nial Tanvir, Nicholas White, Dieter Hartmann, Joseph Hennawi, Amy Lien, Ruben Salvaterra, and Giancarlo Ghirlanda. A.L. acknowledges support, in part, through NASA ATP grant 80NSSC20K0497. Part of this work was done at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Funding AgencyGrant Number
Subject Keywords:Reionization; Early universe
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Reionization (1383); Early universe (435)
Record Number:CaltechAUTHORS:20210914-225358513
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Official Citation:Adam Lidz et al 2021 ApJ 917 58
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110889
Deposited By: George Porter
Deposited On:15 Sep 2021 19:21
Last Modified:15 Sep 2021 19:21

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