Interpreting the transmission windows of distant quasars

A. Maselli, A. Ferrara, S. Gallerani

Research output: Contribution to journalArticlepeer-review


We propose the apparent shrinking criterion (ASC) to interpret the spatial extent, Rw, of transmitted flux windows in the absorption spectra of high-z quasars. The ASC can discriminate between the two regimes in which R w corresponds either to the physical size, RH ii, of the quasar H ii region or to the distance, Rmax w, at which the transmitted flux drops to =0.1 and a Gunn-Peterson (GP) trough appears. In the first case [H ii region (HR) regime], one can determine the intergalactic medium mean H i fraction, xH I; in the second [proximity region (PR) regime], the value of Rw allows one to measure the local photoionization rate and the local enhancement of the photoionization rate, ΓG, due to nearby/intervening galaxies. The ASC has been tested against radiative transfer+smoothed particle hydrodynamics numerical simulations, and applied to a sample of 15 high-z (z > 5.8) quasar spectra. All sample quasars are found to be in the PR regime; hence, their observed spectral properties (inner flux profile, extent of transmission window) cannot reliably constrain the value of xH i. Four sample quasars show evidence for a local enhancement (up to 50 per cent) in the local photoionization rate possibly produced by a galaxy overdensity. We discuss the possible interpretations and uncertainties of this result.

Original languageEnglish
Pages (from-to)1925-1933
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - Jun 2009


  • Cosmology: theory
  • Intergalactic medium
  • Large scale structure of Universe
  • Methods: numerical
  • Quasars: general
  • Radiative transfer

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics


Dive into the research topics of 'Interpreting the transmission windows of distant quasars'. Together they form a unique fingerprint.

Cite this