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

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: gworseck@aip.de

Received: 18 November 2005
Accepted: 16 January 2006

Abstract

We report the discovery of the faint () quasar QSO 03027-0010 at in the vicinity of Q 0302-003, one of the few quasars observed with STIS to study intergalactic  absorption. Together with another newly discovered QSO at , there are now 6 QSOs known near the line of sight towards Q 0302-003, of which 4 are located within the redshift region covered by the STIS spectrum. We correlated the opacity variations in the  and  Lyman forest spectra with the locations of known quasars. There is no significant proximity effect in the  Lyα forest for any of the QSOs, except for the well-known line of sight effect for Q 0302-003 itself. By comparing the absorption properties in  and , 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 QSO 03027-0010 shows such a hardness increase despite being associated with an overdensity in the  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.