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 (ICM). 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 co-evolution 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 ≈ 4 Jy/sr (≈ −5 Jy/sr) at 2250 GHz (940 GHz). In contrast to the usual tSZ effect, the distortion to the CIB spectrum has two null frequencies, at approximately 196 GHz 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 4σ, but foreground contamination reduces the projected signal-to-noise by a factor of ≈ 40. A future ESA Voyage 2050 spectrometer would detect the CIB distortion at ≈ 2-10σ 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.

The SZ effect with anisotropic distributions and high energy electrons

“…It was also shown that the scattering of the CIB by clusters can in principle be used to study the evolution of this background [49,50]. The expressions given here can be used to improve the modeling including non-thermal effects and anisotropies in the distribution functions.…”