Scale-dependent bias in the baryonic-acoustic-oscillation-scale intergalactic neutral hydrogen

I discuss fluctuations in the neutral hydrogen density of the z approximate to 2.3 intergalactic medium and show that their relation to cosmic overdensity is strongly scale dependent. This behavior arises from a linearized version of the well-known proximity effect, in which bright sources suppress atomic hydrogen density. Using a novel, systematic and detailed linear-theory radiative-transfer calculation, I demonstrate how HI density consequently anticorrelates with total matter density when averaged on scales exceeding the Lyman-limit mean-free path. The radiative-transfer thumbprint is highly distinctive and should be measurable in the Lyman-alpha forest. Effects extend to sufficiently small scales to generate significant distortion of the correlation function shape around the baryon acoustic oscillation peak, although the peak location shifts only by 1.2 percent for a mean source bias of b(j) = 3. The distortion changes significantly with b(j) and other astrophysical parameters; measuring it should provide a helpful observational constraint on the nature of ionizing photon sources in the near future.