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X-rays and hard ultraviolet radiation from the first galaxies: ionization bubbles and 21-cm observations

Venkatesan, Aparna and Benson, Andrew (2011) X-rays and hard ultraviolet radiation from the first galaxies: ionization bubbles and 21-cm observations. Monthly Notices of the Royal Astronomical Society, 417 (3). pp. 2264-2275. ISSN 0035-8711. doi:10.1111/j.1365-2966.2011.19407.x.

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The first stars and quasars are known sources of hard ionizing radiation in the first billion years of the Universe. We examine the joint effects of X-rays and hard ultraviolet (UV) radiation from such first-light sources on the hydrogen and helium reionization of the intergalactic medium (IGM) at early times, and the associated heating. We study the growth and evolution of individual H ii, He ii and He iii regions around early galaxies with first stars and/or quasi-stellar object populations. We find that in the presence of helium-ionizing radiation, X-rays may not dominate the ionization and thermal history of the IGM at z ~ 10–20, contributing relatively modest increases to IGM ionization and heating up to ~10^3–10^5 K in IGM temperatures. We also calculate the 21-cm signal expected from a number of scenarios with metal-free starbursts and quasars in varying combinations and masses at these redshifts. The peak values for the spin temperature reach ~10^4–10^5 K in such cases. The maximum values for the 21-cm brightness temperature are around 30–40 mK in emission, while the net values of the 21-cm absorption signal range from ~a few to 60 mK on scales of 0.01–1 Mpc. We find that the 21-cm signature of X-ray versus UV ionization could be distinct, with the emission signal expected from X-rays alone occurring at smaller scales than that from UV radiation, resulting from the inherently different spatial scales at which X-ray and UV ionization/heating manifests. This difference is time-dependent and becomes harder to distinguish with an increasing X-ray contribution to the total ionizing photon production. Such differing scale-dependent contributions from X-ray and UV photons may therefore ‘blur’ the 21-cm signature of the percolation of ionized bubbles around early haloes (depending on whether a cosmic X-ray or UV background is built up first) and affect the interpretation of 21-cm data constraints on reionization.

Item Type:Article
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URLURL TypeDescription DOIArticle
Benson, Andrew0000-0001-5501-6008
Additional Information:© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2011 July 7. Received 2011 July 5; in original form 2011 February 26. Article first published online: 12 Sep 2011. AV gratefully acknowledges support from the Research Corporation through the Single Investigator Cottrell College Science Award and from the University of San Francisco Faculty Development Fund. AB acknowledges the support of the Gordon & Betty Moore Foundation. We thank the referee for a constructive report, and Massimo Ricotti, Xuelei Chen and Steve Furlanetto for useful input.
Group:Moore Center for Theoretical Cosmology and Physics
Funding AgencyGrant Number
Cottrell Scholar of Research CorporationUNSPECIFIED
University of San FranciscoUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Subject Keywords:stars: Population III; galaxies: high-redshift; intergalactic medium; quasars: general; cosmology: theory; dark ages, reionization, first stars
Issue or Number:3
Record Number:CaltechAUTHORS:20111213-103109741
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Official Citation:Venkatesan, A. and Benson, A. (2011), X-rays and hard ultraviolet radiation from the first galaxies: ionization bubbles and 21-cm observations. Monthly Notices of the Royal Astronomical Society, 417: 2264–2275. doi: 10.1111/j.1365-2966.2011.19407.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28442
Deposited By: Ruth Sustaita
Deposited On:13 Dec 2011 19:01
Last Modified:09 Nov 2021 16:57

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