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The epoch of cosmic heating by early sources of X-rays

Eide, MB; Graziani, L; Ciardi, B; Feng, Y; Kakiichi, K; Di Matteo, T; (2018) The epoch of cosmic heating by early sources of X-rays. Monthly Notices of the Royal Astronomical Society , 476 (1) pp. 1174-1190. 10.1093/mnras/sty272. Green open access

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Abstract

Observations of the 21 cm line from neutral hydrogen indicate that an epoch of heating (EoH) might have preceded the later epoch of reionization. Here we study the effects on the ionization state and the thermal history of the intergalactic medium (IGM) during the EoH induced by different assumptions on ionizing sources in the high-redshift Universe: (i) stars; (ii) X-ray binaries (XRBs); (iii) thermal bremsstrahlung of the hot interstellar medium (ISM); and (iv) accreting nuclear black holes (BHs). To this aim, we post-process outputs from the (100 h−1 comoving Mpc)3 hydrodynamical simulation MassiveBlack-II with the cosmological 3D radiative transfer code CRASH, which follows the propagation of ultraviolet and X-ray photons, computing the thermal and ionization state of hydrogen and helium through the EoH. We find that stars determine the fully ionized morphology of the IGM, while the spectrally hard XRBs pave way for efficient subsequent heating and ionization by the spectrally softer ISM. With the seeding prescription in MassiveBlack-II, BHs do not contribute significantly to either ionization or heating. With only stars, most of the IGM remains in a cold state (with a median T = 11 K at z = 10), however, the presence of more energetic sources raises the temperature of regions around the brightest and more clustered sources above that of the cosmic microwave background, opening the possibility to observing the 21 cm signal in emission.

Type: Article
Title: The epoch of cosmic heating by early sources of X-rays
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/sty272
Publisher version: https://doi.org/10.1093/mnras/sty272
Language: English
Additional information: This is the published version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: radiative transfer – dark ages, reionization, first stars
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10055350
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