2002MNRAS.336..587P

The proximity effect evident in the spectra of quasars, that is the deficit of Lyman α forest lines at redshifts close to that of the quasar, is attributed to the ionizing radiation of the quasar itself. The physical extent of the deficient (i.e. more ionized) region will clearly depend on the absolute luminosity of the quasar. However, what we observe will be a relationship involving a redshift range (the clearing in the forest) and the apparent quasar luminosity. The translations from redshift interval to physical scale in the radial direction and from apparent to absolute luminosity depend on the chosen cosmological model, and moreover depend on the model (specifically the density parameter and cosmological constant) in different ways. Analysis of the proximity effect therefore provides a potential test of cosmological parameters. In practice, though moderately large, the effects turn out to be difficult to disentangle from other factors, in particular the value of the intergalactic ionizing flux. Reversing this argument, though, means that the effects can be important (at the 40 per cent level of uncertainty) when attempting to deduce the ionizing background flux and its variation with redshift.