Journal Article

The impact of Lyman series photons on the intergalactic medium during the Epoch of Reionization

Avery Meiksin

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 3, pages 1780-1795
Published in print March 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.16000.x
The impact of Lyman series photons on the intergalactic medium during the Epoch of Reionization

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The role of higher order Lyman series photons in the 21 cm absorption or emission signature of the intergalactic medium (IGM) against the background cosmic microwave background (CMB) during the Epoch of Reionization is examined. It is shown that, taking into account the diminishing resonance line scattering cross-section with increasing Lyman order, a non-negligible net scattering rate of higher order Lyman photons is expected. The resulting radiative cascades will substantially enhance the number density of Lyα photons near a radiation source. It is also shown that the higher order Lyman series photons are able to collisionally heat the IGM by amounts of tens to hundreds of degrees kelvin. The possibility that the Wouthuysen–Field effect may be suppressed by the presence of dust near a galaxy is discussed, and it is shown that the higher order Lyman series photons would still induce the effect, but with a somewhat reduced 21 cm radiation efficiency. It is also demonstrated that extended low surface brightness emission-line haloes will be produced from radiative cascades following the scattering of higher order Lyman series photons. These haloes would provide a unique means of confirming that reionization source candidates were surrounded by an IGM that was still largely neutral on large scales.

Keywords: atomic processes; line: formation; radiative transfer; scattering; cosmology: theory; radio lines: general

Journal Article.  12751 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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