Issue |
A&A
Volume 473, Number 3, October III 2007
|
|
---|---|---|
Page(s) | 805 - 818 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20077585 | |
Published online | 06 August 2007 |
The transverse proximity effect in spectral hardness on the line of sight towards HE 2347–4342 *
1
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: gworseck@aip.de
2
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
3
Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
Received:
2
April
2007
Accepted:
31
July
2007
We report the discovery of 14 quasars in the vicinity of
HE 2347-4342, one of the two quasars whose intergalactic
forest has been resolved with FUSE. By analysing the
and the
opacity variations separately, no transverse proximity effect is
detected near three foreground quasars of HE 2347-4342:
QSO J23503-4328 (
,
), QSO J23500-4319
(
,
) and QSO J23495-4338
(
,
). This is primarily due to line
contamination and overdensities probably created by large-scale structure.
By comparing the
absorption and the corresponding
absorption, we
estimated the fluctuating spectral shape of the extragalactic UV radiation field
along this line of sight. We find that the UV spectral shape near HE 2347-4342
and in the projected vicinity of the three foreground quasars is statistically
harder than expected from UV background models dominated by quasars.
In addition, we find three highly ionised metal line systems near the quasars.
However, they do not yield further constraints on the shape of the ionising field.
We conclude that the foreground quasars show a transverse proximity effect that
is detectable as a local hardening of the UV radiation field, although the
evidence is strongest for QSO J23495-4338. Thus, the relative spectral
hardness traces the proximity effect also in overdense regions prohibiting the
traditional detection in the
forest. Furthermore, we emphasise that
softening of quasar radiation by radiative transfer in the intergalactic medium
is important to understand the observed spectral shape variations. From the
transverse proximity effect of QSO J23495-4338 we obtain a lower limit on the
quasar lifetime of ~25 Myr.
Key words: galaxies: quasars: general / galaxies: quasars: absorption lines / galaxies: intergalactic medium / cosmology: diffuse radiation
© ESO, 2007
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