The effects of UV background correlations on LyA forest flux statistics

Abstract

We examine the possible effects of UV background fluctuations on the pixel flux power spectrum and auto-correlation function of the LyA forest due to a finite number of sources in an attenuating medium. We consider scenarios in which QSO sources dominate the contribution to the UV background. To estimate their contribution, we use the QSO luminosity functions from the 2dF and Sloan QSO surveys. We estimate self-consistent values for the attenuation length at the Lyman edge through the Intergalactic Medium using Particle Mesh simulations of the LyA forest, normalised by the measured mean LyA flux. We examine the convergence properties of the flux power spectrum and auto-correlation function under differing assumptions regarding pressure-smoothing. Convergence to better than 10% in the flux power spectrum at proper wavenumbers k < 0.015s/km requires a comoving resolution of 30-60kpc/h in a comoving box of size 25Mpc/h at z = 5, with the requirements becoming more severe at lower redshifts. We find much better covergence properties for the relative effects of the UV background fluctuations on the flux power spectrum. The background fluctuations increase the large-scale power and suppress the power at intermediate scales. At z < 4, the effect is only at the few percent level. By z > 5, however, the large-scale power is boosted by more than 50%, suggesting the flux power spectrum may serve as a useful tool for distinguishing QSO-dominated UV background scenarios from those dominated by galaxies.

21 pages, LaTeX file with embedded Postscript figures; submitted to MNRAS

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