Recovery of the mass power spectrum from the Lyman-alpha forest: The effect of ionizing background fluctuations from discrete QSO sources

Abstract

In gravitational instability models, there is a close relationship between most Lyman-alpha absorption and the matter density along the line of sight. Croft et al. (1997) have shown that it is possible to use this relationship with some additional assumptions (such as Gaussianity of the initial density) to recover the power spectrum of mass fluctuations, P(k), from QSO absorption spectra. The relative uniformity of the ionizing radiation background on the scales of interest is an additional assumption required by the technique. Here we examine the fluctuations in Lyman-alpha spectra caused if the ionizing background radiation is generated by discrete QSO sources. We present our results alongside the preliminary application of the P(k) recovery technique to the QSO Q1422+231. We find the ionizing background fluctuations to have an effect orders of magnitude smaller than the matter fluctuations at the scales on which we measure P(k) (lambda < 10 h^-1Mpc).