Astronomy & Astrophysics

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Issue		A&A Volume 397, Number 3, January III 2003
Page(s)		891 - 898
Section		Galactic structure and dynamics
DOI		10.1051/0004-6361:20021579

A&A 397, 891-898 (2003)
DOI: 10.1051/0004-6361:20021579

Caught in the act: A helium-reionizing quasar near the line of sight to Q0302-003

P. Jakobsen¹, R. A. Jansen^{1, 2}, S. Wagner³ and D. Reimers⁴

¹ Astrophysics Division, RSSD, European Space Agency, ESTEC, 2200 AG Noordwijk, The Netherlands
² Department of Physics and Astronomy, Arizona State University, Tempe AZ 85287-1504, USA
³ Landessternwarte Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁴ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

(Received 23 October 2002 / Accepted 30 October 2002 )

Abstract
We report the discovery of a quasar at $z=3.050\pm0.003$ , closely coincident in redshift with the isolated low-opacity feature seen near $z\simeq 3.056$ in the otherwise black portion of the $\ion{ii}$ Gunn-Peterson absorption trough seen toward the z=3.286 background quasar Q0302-003, located $6\farcm5$ away on the sky. We explore plausible models for the $\ion{iii}$ ionization zone created by this neighboring quasar and its interception with the line of sight toward Q0302-003. At its present brightness of $V\simeq 20.5$ and separation of $D_\perp\simeq3.2$ Mpc, the quasar can readily account for the opacity gap in the $\ion{ii}$ absorption spectrum of Q0302-003, provided it has been active for $t_Q\ga 10^7$ y. This is the first clear example of the "transverse" proximity effect and the association of a quasar with its imprint on the intervening absorption detected along an adjacent line of sight.

Key words: quasars: individual: QSO 03020-0014, Q0302-003 -- quasars: absorption lines -- intergalactic medium

Offprint request: P. Jakobsen, pjakobsen@rssd.esa.int

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