Inverse-Compton scattering of the cosmic infrared background

Abstract

The thermal Sunyaev-Zel'dovich (tSZ) effect is the distortion generated in the cosmic microwave background (CMB) spectrum by the inverse-Compton scattering of CMB photons off free, energetic electrons, primarily located in the intracluster medium. Cosmic infrared background (CIB) photons from thermal dust emission in star-forming galaxies are expected to undergo the same process. In this work, we perform the first calculation of the resulting tSZ-like distortion in the CIB. Focusing on the CIB monopole, we use a halo model approach to calculate both the CIB signal and the Compton-$y$ field that generates the distortion. We self-consistently account for the redshift coevolution of the CIB and Compton-$y$ fields: they are (partially) sourced by the same dark matter halos, which introduces new aspects to the calculation as compared to the CMB case. We find that the inverse-Compton distortion to the CIB monopole spectrum has a positive (negative) peak amplitude of $\ensuremath{\approx}4\text{ }\text{ }\mathrm{Jy}/\mathrm{sr}$ ($\ensuremath{\approx}\ensuremath{-}5\text{ }\text{ }\mathrm{Jy}/\mathrm{sr}$) at 2260 GHz (940 GHz). In contrast to the usual tSZ effect, the distortion to the CIB spectrum has two null frequencies, at approximately 196 and 1490 GHz. We perform a Fisher matrix calculation to forecast the detectability of this new distortion signal by future experiments. PIXIE would have sufficient instrumental sensitivity to detect the signal at $4\ensuremath{\sigma}$, but foreground contamination reduces the projected signal-to-noise by a factor of $\ensuremath{\approx}70$. A future ESA Voyage 2050 spectrometer could detect the CIB distortion at $\ensuremath{\approx}5\ensuremath{\sigma}$ significance, even after marginalizing over foregrounds. A measurement of this signal would provide new information on the star formation history of the Universe, and the distortion anisotropies may be accessible by near-future ground-based experiments.