Using the sample variance of 21 cm maps as a tracer of the ionisation topology
Abstract
Intensity mapping of the 21 cm signal of neutral hydrogen will yield exciting insights into the Epoch of Reionisation and the nature of the first galaxies. However, the large amount of data that will be generated by the next generation of radio telescopes, such as the Square Kilometre Array, as well as the numerous observational obstacles to overcome, require analysis techniques tuned to extract the reionisation history and morphology. In this context, we introduce a onepoint statistic, which we refer to as the local variance, σ_{loc}, that describes the distribution of the mean differential 21 cm brightness temperatures measured in twodimensional maps along the frequency direction of a light cone. The local variance takes advantage of what is usually considered an observational bias, the sample variance. We find the redshiftevolution of the local variance to not only probe the reionisation history of the observed patches of the sky, but also trace the ionisation morphology. This estimator provides a promising tool to constrain the midpoint of reionisation as well as gain insight into the ionising properties of early galaxies.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 September 2021
 DOI:
 10.1051/00046361/202140515
 arXiv:
 arXiv:2102.04352
 Bibcode:
 2021A&A...653A..58G
 Keywords:

 dark ages;
 reionization;
 first stars;
 methods: statistical;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 14 pages, 14 figures, published in A&