---
_id: '17721'
abstract:
- lang: eng
  text: High-redshift quasars (z >~ 6) drive ionization fronts into the intergalactic
    medium (IGM). If the thickness of the front can be measured, it can provide a
    novel constraint on the ionizing spectral energy distribution (SED). Here we follow
    the propagation of an I-front into a uniform IGM, and compute its thickness for
    a range of possible quasar spectra and ages. We also explore the effects of uniform
    and non-uniform ionizing backgrounds. We find that even for hard spectra, the
    fronts are initially thin, with a thickness much smaller than the mean free path
    of ionizing photons, but the thickness increases as the front approaches equilibrium
    in 10^8 - 10^9 years, and can eventually significantly exceed simple estimates
    based on the mean free path. With a high intrinsic hydrogen column density obscuring
    the source (log(N_H/cm^-2) >~ 19.2) or a hard power-law spectrum combined with
    some obscuration (e.g. dlog(F_\nu)/dlog(\nu) >~ -1.2 at log(N_H/cm^-2) >~ 18.0),
    the thickness of the front exceeds ~1 physical Mpc and may be measurable from
    the morphology of its redshifted 21cm signal. We find that the highly ionized
    inner part of the front, which may be probed by Lyman line absorption spectra,
    remains sharp for bright quasars unless a large obscuring column (log(N_H/cm^-2)
    >~ 19.2) removes most of their ionizing photons up to ~40 eV. For obscured sources
    with log(N_H/cm^-2) >~ 19.8, embedded in a significantly neutral IGM, the black
    Lyman-alpha trough (where the neutral fraction is ~10^-3) underestimates the size
    of the HII region by a factor of >~4.
article_processing_charge: No
article_type: original
author:
- first_name: R. H.
  full_name: Kramer, R. H.
  last_name: Kramer
- first_name: Zoltán
  full_name: Haiman, Zoltán
  id: 7c006e8c-cc0d-11ee-8322-cb904ef76f36
  last_name: Haiman
citation:
  ama: Kramer RH, Haiman Z. The thickness of high-redshift quasar ionization fronts
    as a constraint on the ionizing spectral energy distribution. <i>Monthly Notices
    of the Royal Astronomical Society</i>. 2008;385(3):1561-1575. doi:<a href="https://doi.org/10.1111/j.1365-2966.2008.12945.x">10.1111/j.1365-2966.2008.12945.x</a>
  apa: Kramer, R. H., &#38; Haiman, Z. (2008). The thickness of high-redshift quasar
    ionization fronts as a constraint on the ionizing spectral energy distribution.
    <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press.
    <a href="https://doi.org/10.1111/j.1365-2966.2008.12945.x">https://doi.org/10.1111/j.1365-2966.2008.12945.x</a>
  chicago: Kramer, R. H., and Zoltán Haiman. “The Thickness of High-Redshift Quasar
    Ionization Fronts as a Constraint on the Ionizing Spectral Energy Distribution.”
    <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press,
    2008. <a href="https://doi.org/10.1111/j.1365-2966.2008.12945.x">https://doi.org/10.1111/j.1365-2966.2008.12945.x</a>.
  ieee: R. H. Kramer and Z. Haiman, “The thickness of high-redshift quasar ionization
    fronts as a constraint on the ionizing spectral energy distribution,” <i>Monthly
    Notices of the Royal Astronomical Society</i>, vol. 385, no. 3. Oxford University
    Press, pp. 1561–1575, 2008.
  ista: Kramer RH, Haiman Z. 2008. The thickness of high-redshift quasar ionization
    fronts as a constraint on the ionizing spectral energy distribution. Monthly Notices
    of the Royal Astronomical Society. 385(3), 1561–1575.
  mla: Kramer, R. H., and Zoltán Haiman. “The Thickness of High-Redshift Quasar Ionization
    Fronts as a Constraint on the Ionizing Spectral Energy Distribution.” <i>Monthly
    Notices of the Royal Astronomical Society</i>, vol. 385, no. 3, Oxford University
    Press, 2008, pp. 1561–75, doi:<a href="https://doi.org/10.1111/j.1365-2966.2008.12945.x">10.1111/j.1365-2966.2008.12945.x</a>.
  short: R.H. Kramer, Z. Haiman, Monthly Notices of the Royal Astronomical Society
    385 (2008) 1561–1575.
date_created: 2024-09-06T09:09:01Z
date_published: 2008-03-13T00:00:00Z
date_updated: 2024-09-25T13:54:14Z
day: '13'
doi: 10.1111/j.1365-2966.2008.12945.x
extern: '1'
fulldoi: https://doi.org/10.1111/j.1365-2966.2008.12945.x
intvolume: '       385'
issue: '3'
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://doi.org/10.1111/j.1365-2966.2008.12945.x
month: '03'
oa: 1
oa_version: Published Version
page: 1561-1575
publication: Monthly Notices of the Royal Astronomical Society
publication_identifier:
  issn:
  - 0035-8711
  - 1365-2966
publication_status: published
publisher: Oxford University Press
quality_controlled: '1'
scopus_import: '1'
status: public
title: The thickness of high-redshift quasar ionization fronts as a constraint on
  the ionizing spectral energy distribution
type: journal_article
user_id: 317138e5-6ab7-11ef-aa6d-ffef3953e345
volume: 385
year: '2008'
...