Opening the 21-cm window into the Cosmic Dawn with NenuFAR
The Cosmic Dawn is the period when the first stars formed in the Universe, a few hundred million years after the Big Bang. As these stars formed, their radiation began to ionize the surrounding neutral hydrogen, marking the beginning of the Epoch of Reionization.
The 21-cm signal, a spectral line of neutral hydrogen, provides a way to trace this neutral gas during the early stages of the Universe. As the 21-cm signal travels through the expanding cosmos, its wavelength is stretched (redshifted) to meter scales, where it can be observed using low-frequency radio telescopes. Radio interferometers can measure the spatial fluctuations of this redshifted 21-cm signal, offering a powerful probe of these largely unexplored periods in the history of the Universe. Detecting this faint background signal, however, is extremely challenging because it is buried beneath bright foregrounds and instrumental effects that obscure our view.
NenuFAR is a new radio interferometer in France, and a powerful 21-cm cosmology instrument capable of detecting the 21-cm signal from the Cosmic Dawn. In his thesis, Satyapan Munshi used NenuFAR to place the strongest constraints to date on the 21-cm signal power spectrum during the Cosmic Dawn. Munshi also developed new analytical equations, algorithms, and statistical methods to understand and mitigate the dominant contaminants that limit our ability to detect the signal. These efforts lay the groundwork for the future detection of the Cosmic Dawn 21-cm signal with NenuFAR and other upcoming instruments such as the Square Kilometre Array.