The proximity effect in a close group of QSOs |
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Authors: | J. Liske G.M. Williger |
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Affiliation: | 1School of Physics, University of New South Wales, Sydney 2052, Australia;2NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA |
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Abstract: | We present an analysis of the proximity effect in a sample of 10 2-Å-resolution QSO spectra of the Ly α forest at . Rather than investigating variations in the number density of individual absorption lines, we employ a novel technique that is based on the statistics of the transmitted flux itself. We confirm the existence of the proximity effect at the > 99 per cent confidence level. We derive a value for the mean intensity of the extragalactic background radiation at the Lyman limit of . This value assumes that QSO redshifts measured from high-ionization lines differ from the true systemic redshifts by . We find evidence at a level of 2.6 σ that the significance of the proximity effect is correlated with QSO Lyman limit luminosity. Allowing for known QSO variability, the significance of the correlation reduces to 2.1 σ . The QSOs form a close group on the sky and the sample is thus well suited for an investigation of the foreground proximity effect, where the Ly α forest of a background QSO is influenced by the UV radiation from a nearby foreground QSO. From the complete sample we find no evidence for the existence of this effect, implying either that or that QSOs emit at least a factor of 1.4 less ionizing radiation in the plane of the sky than along the line of sight to Earth. We do, however, find one counter-example. Our sample includes the fortunate constellation of a foreground QSO surrounded by four nearby background QSOs. These four spectra all show underdense absorption within ±3000 km s−1 of the redshift of the foreground QSO. |
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Keywords: | intergalactic medium quasars: absorption lines diffuse radiation |
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