Exploring the evolution of reionization using a wavelet transform and the light cone effect
Abstract
The Cosmic Dawn and Epoch of Reionization, during which collapsed structures produce the first ionizing photons and proceed to reionize the intergalactic medium, span a large range in redshift (z ∼ 306) and time (t_{age} ∼ 0.11.0 Gyr). Exploration of these epochs using the redshifted 21 cm emission line from neutral hydrogen is currently limited to statistical detection and estimation metrics (e.g. the power spectrum) due to the weakness of the signal. Brightness temperature fluctuations in the lineofsight dimension are probed by observing the emission line at different frequencies, and their structure is used as a primary discriminant between the cosmological signal and contaminating foreground extragalactic and Galactic continuum emission. Evolution of the signal over the observing bandwidth leads to the `line cone effect' whereby the H I structures at the start and end of the observing band are not statistically consistent, yielding a biased estimate of the signal power, and potential reduction in signal detectability. We implement a wavelet transform to wide bandwidth radio interferometry experiments to probe the local statistical properties of the signal. We show that use of the wavelet transform yields estimates with improved estimation performance, compared with the standard Fourier Transform over a fixed bandwidth. With the suite of current and future large bandwidth reionization experiments, such as with the 300 MHz instantaneous bandwidth of the Square Kilometre Array, a transform that retains local information will be important.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 September 2016
 DOI:
 10.1093/mnras/stw1310
 arXiv:
 arXiv:1605.07256
 Bibcode:
 2016MNRAS.461..126T
 Keywords:

 methods: statistical;
 techniques: interferometric;
 dark ages;
 reionization;
 first stars;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 11 pages, 7 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society