Measurements of the UV background at 4.6 < z < 6.4 using the quasar proximity effect

摘要: We present measurements of the ionising ultraviolet background (UVB) at z ~ 5-6 using quasar proximity effect. The fifteen quasars in our sample cover range 4.6 5. metagalactic hydrogen ionisation rate, Gamma_bkg, was determined by modelling combined field from and UVB zone on a pixel-by-pixel basis. optical depths spectra were corrected for expected effect until mean flux region equalled that average Ly-alpha forest, this we make measurement Gamma_bkg. A number systematic effects tested synthetic spectra. Noise found to be largest source bias 5, while uncertainties transmitted are responsible 6. impacts large-scale overdensities Lyman limit systems Gamma_bkg also investigated, but small > find decline with redshift, log(Gamma_bkg) = -12.15 $\pm$ 0.16 5 -12.84 0.18 6 (1 sigma errors). Compared lower redshifts, suggest drop factor five HI photoionisation rate between 4 appears gradual, no evidence sudden change any redshift would indicate rapid attenuation length photons. Combined recent evolution free path photons, results imply emissivity photons roughly two 6, albeit significant uncertainty due errors both path.