Spectral energy distribution of the metagalactic ionizing radiation field from QSO absorption spectra

Free access article

Issue		A&A Volume 441, Number 1, October I 2005


Page(s)		9 - 21
Section		Cosmology (including clusters of galaxies)
DOI		http://dx.doi.org/10.1051/0004-6361:20052960

A&A 441, 9-21 (2005)
DOI: 10.1051/0004-6361:20052960

Spectral energy distribution of the metagalactic ionizing radiation field from QSO absorption spectra

I. I. Agafonova¹, M. Centurión², S. A. Levshakov¹ and P. Molaro²

¹ Department of Theoretical Astrophysics, Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia
e-mail: lev@astro.ioffe.rssi.ru
² Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy

(Received 1 March 2005 / Accepted 30 May 2005 )

Abstract
A computational procedure is presented to estimate the spectral shape of the ionizing background between 1 and 10 Ryd by analyzing optically thin absorption systems in the spectra of high redshift quasars. The procedure is based on the response surface methodology from the theory of experimental design. The shape of the recovered UV background at $z \sim 3$ shows a significant intensity decrease between 3 and 4 Ryd compared to the metagalactic spectrum of Haardt & Madau (1996, ApJ, 461, 20). This decrease is interpreted as produced by $\ion{He}{ii}$ Gunn-Peterson effect. There are no features indicating a contribution from galaxies to the UV background which is therefore dominated by QSOs at $z \sim 3$ .

Key words: cosmology: observations -- line: formation -- line: profiles -- Galaxy: abundances -- galaxies: quasars: absorption lines

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