Revisiting secondary CMB distortions due to kinetic Sunyaev-Zel'dovich effect from quasar bubbles before reionization

TL;DR

This paper analyzes the secondary CMB anisotropy caused by quasar bubbles before reionization, improving previous models and suggesting potential detectability with future high-resolution surveys like CMB-HD.

Contribution

It introduces an improved halo model-based calculation of quasar bubble kSZ effects and distinguishes their spectral shape from galaxy-driven reionization signals.

Findings

Quasar bubble kSZ signal is sub-dominant to galaxy-driven reionization.

Distinct peak in the power spectrum at $\, ext{ell} \, ext{approx} 500-700$ for quasar bubbles.

Single quasar bubbles could be detected with future high-resolution CMB experiments.

Abstract

We discuss the secondary cosmic microwave background (CMB) anisotropy due to kinetic Sunyaev-Zel'dovich (kSZ) effect from ionized bubbles around individual quasars prior to the reionization of the Universe. The bubbles create local ionization modulations which move with the large scale structure linear bulk flow and act as sources for kSZ. We improve upon previous calculations of this effect, using a halo model based description of quasar abundance, and find that the kSZ distortion power spectrum, $C_\ell$, from the bubbles to be sub-dominant to kSZ from patchy reionization driven by galaxies. However, the shape of the two $C_\ell$'s are very different with the quasar bubble $C_\ell$ having a peak at $\ell \approx 500-700$ whereas the $C_\ell$ due to patchy reionization flattening out at $\ell > 1000$ thus making it plausible to separate the two using $C_\ell$ template-fitting in a future survey like CMB-HD. Next, we look at the imprint of a single quasar bubble on the CMB and show that it can be detected in a high-resolution, ambitious effort like CMB-HD. A detection of a high redshift quasar bubble in the CMB would carry complimentary information to its detection in HI or Lyman-$\alpha$ and a joint analysis can be used to break parameter degeneracies.