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

Abstract

We report the discovery of a quasar at z=3.050+/-0.003, closely coincident in redshift with the isolated low-opacity feature seen near z =~ 3.056 in the otherwise black portion of the He Ii Gunn-Peterson absorption trough seen toward the z=3.286 background quasar Q0302-003, located 6farcm5 away on the sky. We explore plausible models for the He 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 =~ 20.5 and separation of D_{perpendicular} to =~ 3.2 Mpc, the quasar can readily account for the opacity gap in the He Ii absorption spectrum of Q0302-003, provided it has been active for t_Q>~ 10⁷ 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.

Based on observations collected at the European Southern Observatory, Chile (Proposals 66.A-0307 and 68.A-0194).