| Issue |
A&A
Volume 483, Number 1, May III 2008
|
|
|---|---|---|
| Page(s) | 19 - 34 | |
| Section | Cosmology (including clusters of galaxies) | |
| DOI | https://doi.org/10.1051/0004-6361:20079109 | |
| Published online | 19 March 2008 | |
EUV spectral energy distribution of quasars restored from associated absorbers*
1
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: lev@astro.ioffe.rssi.ru
2
Shanghai Astronomical Observatory, 80 Nandan Road, Shanghai 200030, PR China
3
Ioffe Physico-Technical Institute, Polytekhnicheskaya Str. 26, 194021 St. Petersburg, Russia
4
Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy
Received:
20
November
2007
Accepted:
5
February
2008
Aims. We reconstruct the spectral shape of the quasar ionizing radiation in the extreme-UV range (1 Ryd ≤ E < 10 Ryd) from the analysis of narrow absorption lines (NAL) of the associated systems.
Methods. The computational technique for inverse spectroscopic problems – a Monte Carlo Inversion augmented by the spectral shape recovering procedure and modified to account for the incomplete coverage of the light source is used to analyze observations.
Results. The ionizing spectra responsible for the ionization structure
of the NAL systems require an intensity depression
at 
Ryd which is attributed to the 
Lyman continuum
opacity (
).
A most likely source of this opacity is a quasar
accretion disk wind. The corresponding column density of 
in the wind is
estimated as a few times 1016 cm-2.
This amount of neutral hydrogen should cause
a weak continuum depression at 
Å (rest-frame),
and a broad and shallow absorption in Ly-α.
If the metallicity of the wind is high enough,
other resonance lines of 
, 
-
, etc.
are expected. In the analyzed QSO spectra we do observe
broad (stretching over 1000s km s-1)
and shallow (
) absorption troughs
of Ly-α and 
as well as continuum depressions at Å
which correspond to N() ~ 5 
1016 cm-2.
Observational data available in both the UV and X-ray ranges suggest
that at least ~50% of the quasar radiation
passes through the gas opaque in the Lyman continuum.
This means that the outcoming ionizing spectrum should have a pronounced
intensity break at Ryd with the depth of this break
depending on the angle with the rotational axis of the accretion disk
(the larger the angle the deeper the break).
The QSO spectra with a discontinuity at 4 Ryd
can influence the rate of reionization
in the intergalactic medium and partly explain the inhomogeneous (patchy)
ionization structure of the intergalactic observed at 
.
Key words: cosmology: observations / line: formation / line: profiles / quasars: absorption lines
© ESO, 2008
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