Primordial Non-Gaussianity and Reionization

TL;DR

This paper explores how primordial non-Gaussianity influences the reionization process and its observable signatures in 21 cm surveys, suggesting potential for future constraints comparable to Planck.

Contribution

It models the impact of primordial non-Gaussianity on the reionization field and assesses the detectability of this effect in upcoming 21 cm observations.

Findings

Primordial non-Gaussianity affects the size and timing of reionization.

The power spectrum of ionization fluctuations exhibits a 1/k^2 dependence on large scales.

Upcoming 21 cm surveys can potentially constrain primordial non-Gaussianity despite foreground challenges.

Abstract

The statistical properties of the primordial perturbations contain clues about the origins of those fluctuations. Although the Planck collaboration has recently obtained tight constraints on primordial non-gaussianity from cosmic microwave background measurements, it is still worthwhile to mine upcoming data sets in effort to place independent or competitive limits. The ionized bubbles that formed at redshift z~6-20 during the Epoch of Reionization are seeded by primordial overdensities, and so the statistics of the ionization field at high redshift are related to the statistics of the primordial field. Here we model the effect of primordial non-gaussianity on the reionization field. The epoch and duration of reionization are affected as are the sizes of the ionized bubbles, but these changes are degenerate with variations in the properties of the ionizing sources and the surrounding intergalactic medium. A more promising signature is the power spectrum of the spatial fluctuations in the ionization field, which may be probed by upcoming 21 cm surveys. This has the expected 1/k^2 dependence on large scales, characteristic of a biased tracer of the matter field. We project how well upcoming 21 cm observations will be able to disentangle this signal from foreground contamination. Although foreground cleaning inevitably removes the large-scale modes most impacted by primordial non-gaussianity, we find that primordial non-gaussianity can be separated from foreground contamination for a narrow range of length scales. In principle, futuristic redshifted 21 cm surveys may allow constraints competitive with Planck.