Patchy Screening of the Cosmic Microwave Background by Inhomogeneous Reionization

TL;DR

This paper investigates the potential to constrain inhomogeneous reionization's patchy screening effects on the CMB using WMAP data, and discusses future prospects with upcoming experiments and recent EDGES results.

Contribution

It introduces a phenomenological model linking reionization patchiness to observable CMB correlations and assesses current and future data's ability to constrain these models.

Findings

Current WMAP data cannot constrain reionization patchiness.

Future Planck and EPIC data may probe relevant parameter space.

Recent EDGES results impose additional constraints.

Abstract

We derive a constraint on patchy screening of the cosmic microwave background from inhomogeneous reionization, using off-diagonal TB and TT correlations in WMAP-7 temperature/polarization data. We interpret this as a constraint on the rms optical-depth fluctuation \Delta\tau\ as a function of a coherence multipole Lc. We relate these parameters to a comoving coherence scale, of bubble size Rc, in a phenomenological model where reionization is instantaneous but occurs on a crinkly surface, and also to the bubble size in a model of "Swiss cheese" reionization where bubbles of fixed size are spread over some range of redshifts. The current WMAP data are still too weak, by several orders of magnitude, to constrain reasonable models, but forthcoming Planck and future EPIC data should begin to approach interesting regimes of parameter space. We also present constraints on the parameter space imposed by the recent results from the EDGES experiment.