CMB polarization constraints on radiative feedback

TL;DR

This paper investigates how different radiative feedback models during cosmic reionization affect CMB polarization signals, showing that upcoming experiments could distinguish between these models despite foreground challenges.

Contribution

It introduces a modified Boltzmann code to compare CMB signatures of two reionization models with different feedback mechanisms, highlighting their distinguishability in polarization data.

Findings

Differences in EE mode polarization are detectable over multipole range 5-15.

Predicted spectral distortions are below current limits but within future experiment sensitivity.

Foreground contamination needs to be controlled at percent level for model discrimination.

Abstract

We compute the imprints left on the CMB by two cosmic reionization models consistent with current observations but characterized by alternative radiative feedback prescriptions (suppression and filtering) resulting in a different suppression of star formation in low-mass halos. The models imply different ionization and thermal histories and 21 cm background signals. The derived Comptonization, u, and free-free distortion, y_B, parameters are below current observational limits for both models. However, the value of u = 1.69 * 10^-7 (9.65 * 10^-8) for the suppression (filtering) model is in the detectability range of the next generation of CMB spectrum experiments. Through the dedicated Boltzmann code CMBFAST, modified to include the above ionization histories, we compute the CMB angular power spectrum (APS) of the TT, TE, and EE modes. For the EE mode the differences between these models are significantly larger than the cosmic and sampling variance over the multipole range l = 5-15, leaving a good chance of discriminating between these feedback mechanisms with forthcoming/future CMB polarization experiments. The main limitations come from foreground contamination: it should be subtracted at per cent level in terms of APS, a result potentially achievable by novel component separation techniques and mapping of Galactic foreground.