paper

Quasars near the line of sight towards Q 0302-003 and the transverse proximity effect

arXiv:astro-ph/0601374 · doi:10.1051/0004-6361:20054549

Abstract

We report the discovery of the faint (V=21.7) quasar QSO03027-0010 at z=2.808 in the vicinity of Q0302-003, one of the few quasars observed with STIS to study intergalactic HeII absorption. Together with another newly discovered QSO at z=2.29, there are now 6 QSOs known near the line of sight towards Q0302-003, of which 4 are located within the redshift region 2.76<=z<=3.28 covered by the STIS spectrum. We correlated the opacity variations in the HI and HeII Lyman forest spectra with the locations of known quasars. There is no significant proximity effect in the HI Lyman alpha forest for any of the QSOs, except for the well-known line of sight effect for Q0302-003 itself. By comparing the absorption properties in HI and HeII, we estimated the fluctuating hardness of the extragalactic UV radiation field along this line of sight. We find that close to each foreground quasar, the ionizing background is considerably harder than on average. In particular, our newly discovered QSO03027-0010 shows such a hardness increase despite being associated with an overdensity in the HI Lyman forest. We argue that the spectral hardness is a sensitive physical measure to reveal the influence of QSOs onto the UV background even over scales of several Mpc, and that it breaks the density degeneracy hampering the traditional transverse proximity effect analysis. We infer from our sample that there is no need for significantly anisotropic UV radiation from the QSOs. From the transverse proximity effect detected in the sample we obtain minimum quasar lifetimes in the range ~10-30 Myr.

arXiv comment15 pages, 9 figures, accepted by A&A, problems with paper size fixed

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