Statistics of 21-cm Fluctuations in Cosmic Reionization Simulations: PDFs and Difference PDFs

TL;DR

This paper evaluates the effectiveness of probability distribution functions (PDFs) and difference PDFs as statistical tools for analyzing 21-cm signals from cosmic reionization, offering insights beyond traditional power spectrum methods.

Contribution

It introduces the first measurements of difference PDFs in reionization simulations and assesses their potential to complement existing statistical techniques.

Findings

PDFs probe ionizing source properties

Difference PDFs provide additional reionization information

Statistics are relatively insensitive to small-scale astrophysics

Abstract

In the coming decade, low-frequency radio arrays will begin to probe the epoch of reionization via the redshifted 21-cm hydrogen line. Successful interpretation of these observations will require effective statistical techniques for analyzing the data. Due to the difficulty of these measurements, it is important to develop techniques beyond the standard power spectrum analysis in order to offer independent confirmation of the reionization history, probe different aspects of the topology of reionization, and have different systematic errors. In order to assess the promise of probability distribution functions (PDFs) as statistical analysis tools in 21-cm cosmology, we first measure the 21-cm brightness temperature (one-point) PDFs in six different reionization simulations. We then parametrize their most distinct features by fitting them to a simple model. Using the same simulations, we also present the first measurements of difference PDFs in simulations of reionization. We find that while these statistics probe the properties of the ionizing sources, they are relatively independent of small-scale, sub-grid astrophysics. We discuss the additional information that the difference PDF can provide on top of the power spectrum and the one-point PDF.