On the effect of the ionizing background on the Lyα forest autocorrelation function

Abstract

An analytical framework is presented to understand the effects of a fluctuating intensity of the cosmic ionizing background on the correlations of the Lyα forest transmission fraction measured in quasar spectra. In the absence of intensity fluctuations, the Lyα power spectrum should have the expected cold darkmatter power spectrumwith redshift distortions in the linear regime, with a bias factor bδ and a redshift distortion parameter β that depend on redshift but are independent of scale. The intensity fluctuations introduce a scale dependence in both bδ and β, but keeping their product bδβ fixed. Observations of the Lyα correlations and cross-correlations with radiation sources like those being done at present in the Baryon Oscillation Spectroscopic Survey of Sloan Digital Sky Survey third generation have the potential to measure this scale dependence, which reflects the biasing properties of the sources and absorbers of the ionizing background. We also compute a second term affecting the Lyα spectrum, due to shot noise in the sources of radiation. This term is very large if luminous quasars are assumed to produce the ionizing background and to emit isotropically with a constant luminosity, but should be reduced by a contribution from galaxies, and by the finite lifetime and anisotropic emission of quasars. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.