Imprints of Reionization in Galaxy Clustering

Abstract

Reionization, the only phase transition in the Universe since recombination, is a key event in the cosmic history of baryonic matter. We derive, in the context of the large-scale bias expansion, the imprints of the epoch of reionization in the large-scale distribution of galaxies, and identify two contributions of particular importance. First, the Compton scattering of CMB photons off the free electrons lead to a drag force on the baryon fluid. This drag induces a relative velocity between baryons and CDM which is of the same order of magnitude as the primordially-induced relative velocity, and enters in the evolution of the relative velocity as calculated by Boltzmann codes. This leads to a unique contribution to galaxy bias involving the matter velocity squared. The second important effect is a modulation of the galaxy density by the ionizing radiation field through radiative-transfer effects, which is captured in the bias expansion by so-called higher-derivative terms. We constrain both of these imprints using the power spectrum of the BOSS DR12 galaxy sample. While they do not lead to a shift in the baryon acoustic oscillation scale, including these terms is important for unbiased cosmology constraints from the shape of the galaxy power spectrum.

18 pages, 5 figures; v2: minor improvements, submitted to PRD; v3: clarifications and additions in response to referee, matches published version

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• Galaxy bias from forward models: linear and second-order bias of IllustrisTNG galaxies
• Theoretical Systematics of Future Baryon Acoustic Oscillation Surveys
• Biased Tracers of Two Fluids in the Lagrangian Picture
• Small-scale structure and the Lyman-$\alpha$ forest baryon acoustic oscillation feature
• Responses of Halo Occupation Distributions: a new ingredient in the halo model & the impact on galaxy bias
• A new scale in the bias expansion
• Fast Calculation of Nonlinear Redshift-space Galaxy Power Spectrum Including Selection Bias
• Detecting Baryon Acoustic Oscillations in Dark Matter from Kinematic Weak Lensing Surveys