The impact of temperature fluctuations on the Lyα forest power spectrum

We explore the impact of spatial fluctuations in the intergalactic medium (IGM) temperature on the Ly alpha forest flux power spectrum near z similar to 3. We develop a semianalytic model to examine temperature fluctuations resulting from inhomogeneous H I and incomplete He II reionizations. Detection of these fluctuations might provide insight into the reionization histories of hydrogen and helium. Furthermore, these fluctuations, neglected in previous analyses, could bias constraints on cosmological parameters from the Ly alpha forest. We find that the temperature fluctuations resulting from inhomogeneous H I reionization are likely to be very small, with an rms amplitude of less than or similar to 5%, sigma(T0)/(T-0) less than or similar to 0.05. More important are the temperature fluctuations that arise from incomplete H II reionization, which might plausibly be as large as 50%, sigma(T0)/(T-0) similar to 0.5. In practice, however, these temperature fluctuations have only a small effect on flux power spectrum predictions. The smallness of the effect is possibly due to density fluctuations dominating over temperature fluctuations on the scales probed by current measurements. On the largest scales currently probed, k similar to 0.001 s km(-1) (similar to 0.1 h Mpc(-1)), the effect on the flux power spectrum may be as large as similar to 10% in extreme models. The effect is larger on small scales, up to similar to 20% at k - 0.1 s km(-1), due to thermal broadening. Our results suggest that the omission of temperature fluctuation effects from previous analyses does not significantly bias constraints on cosmological parameters.