Imprints of reionization in galaxy clustering

Fabian Schmidt, Florian Beutler

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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 cosmic microwave background photons off the free electrons lead to a drag force on the baryon fluid. This drag induces a relative velocity between baryons and cold dark matter, 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.
Original languageEnglish
Article number083533
Number of pages16
JournalPhysical Review D
Issue number8
Publication statusPublished - 30 Oct 2017


  • UKSA
  • ST/N00180X/1


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