Journal Article

The impact of a percolating IGM on redshifted 21-cm observations of quasar H <span class="smallCaps">ii</span> regions

Paul M. Geil and J. Stuart B. Wyithe

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 386, issue 3, pages 1683-1694
Published in print May 2008 | ISSN: 0035-8711
Published online April 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13159.x
The impact of a percolating IGM on redshifted 21-cm observations of quasar H ii regions

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We assess the impact of inhomogeneous reionization on detection of H ii regions surrounding luminous high-redshift quasars using planned low-frequency radio telescopes. Our approach is to implement a seminumerical scheme to calculate the three-dimensional structure of ionized regions surrounding a massive halo at high redshift, including the ionizing influence of a luminous quasar. As part of our analysis we briefly contrast our scheme with published seminumerical models. We calculate mock 21-cm spectra along the line of sight towards high-redshift quasars, and estimate the ability of the planned Murchison Widefield Array to detect the presence of H ii regions. The signal-to-noise ratio for detection will drop as the characteristic bubble size grows during reionization because the quasar's influence becomes less prominent. However, quasars will imprint a detectable signature on observed 21-cm spectra that is distinct from a region of typical intergalactic medium (IGM). At epochs where the mean hydrogen neutral fraction is ≈30 per cent or greater we find that neutral gas in the IGM surrounding a single quasar will be detectable (at a significance of 5σ) within 100-h integrations in more than 50 per cent of cases. 1000-h integrations will be required to detect a smaller neutral fraction of 15 per cent in more than 50 per cent of cases. A highly significant detection will be possible in only 100 h for a stack of 10 smaller 3 proper Mpc H ii regions. The accurate measurement of the global average neutral fraction (〈xH i〉) will be limited by systematic fluctuations between lines of sight for single H ii regions. We estimate the accuracy with which the global neutral fraction could be measured from a single H ii region to be 50, 30 and 20 per cent for 〈xH i〉≈ 0.15, 0.3 and 0.5, respectively.

Keywords: galaxies: high-redshift; intergalactic medium; cosmology: theory; diffuse radiation

Journal Article.  8491 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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