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Modeling the Radio Background from the First Black Holes at Cosmic Dawn: Implications for the 21 cm Absorption Amplitude

Ewall-Wice, A. and Chang, T.-C. and Lazio, J. and Doré, O. and Seiffert, M. and Monsalve, R. A. (2018) Modeling the Radio Background from the First Black Holes at Cosmic Dawn: Implications for the 21 cm Absorption Amplitude. Astrophysical Journal, 868 (1). Art. No. 63. ISSN 1538-4357.

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We estimate the 21 cm radio background from accretion onto the first intermediate-mass black holes between z ≈ 30 and z ≈ 16. Combining potentially optimistic, but plausible, scenarios for black hole formation and growth with empirical correlations between luminosity and radio emission observed in low-redshift active galactic nuclei, we find that a model of black holes forming in molecular cooling halos is able to produce a 21 cm background that exceeds the cosmic microwave background (CMB) at z ≈ 17, though models involving larger halo masses are not entirely excluded. Such a background could explain the surprisingly large amplitude of the 21 cm absorption feature recently reported by the EDGES collaboration. Such black holes would also produce significant X-ray emission and contribute to the 0.5–2 keV soft X-ray background at the level of ≈10^(−13)–10^(−12) erg s^(−1)cm^(−2) deg^(−2), consistent with existing constraints. In order to avoid heating the intergalactic medium (IGM) over the EDGES trough, these black holes would need to be obscured by hydrogen column depths of N_H ~ 5 × 10^(23) cm^(−2). Such black holes would avoid violating constraints on the CMB optical depth from Planck if their UV photon escape fractions were below f_(esc) ≾ 0.1, which would be a natural result of N_H ~ 5 × 10^(23) cm^(−2) being imposed by an unheated IGM.

Item Type:Article
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URLURL TypeDescription Paper
Ewall-Wice, A.0000-0002-0086-7363
Doré, O.0000-0002-5009-7563
Monsalve, R. A.0000-0002-3287-2327
Additional Information:© 2018 The American Astronomical Society. Received 2018 March 12; revised 2018 September 18; accepted 2018 September 26; published 2018 November 20. The authors thank Judd Bowman, Adam Lidz, Rennan Barkana, Anastasia Fialkov, and Jordan Mirocha for useful discussions, along with Florian Bolgar for correcting several numerical errors. Calculations in this work were performed using the Colossus library (Diemer 2017). A.E.W.'s contribution was supported by an appointment to the NASA Postdoctoral Program at the California Institute of Technology Jet Propulsion Laboratory. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. R.A.M. was supported by the NASA Solar System Exploration Virtual Institute cooperative agreement 80ARC017M0006.
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NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:dark ages, reionization, first stars
Record Number:CaltechAUTHORS:20181120-104409649
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Official Citation:A. Ewall-Wice et al 2018 ApJ 868 63
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91069
Deposited By: Tony Diaz
Deposited On:20 Nov 2018 18:56
Last Modified:20 Nov 2018 18:56

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