Seminaire Lagrange -- Adelie Gorce (IAS) -- A global picture of the Epoch of Reionisation

About a billion years after the Big Bang, the Epoch of Reionisation saw the first light sources in the Universe slowly ionise the primordial atoms of the surrounding IGM. Learning about this distant epoch has the potential of unveiling crucial information about the formation of the first stars, galaxies, and early black holes, which sourced it. However, its observation remains elusive. Attempted measurements of the 21cm signal, coming directly from the high-redshift neutral hydrogen, are still plagued with foregrounds and systematics, whilst modelling uncertainties prevent us from extracting the reionisation signatures from large astrophysical and cosmological data sets. 

In this talk, I will describe how gigantic radio interferometers in the most remote locations and state-of-the-art CMB telescopes can tell us about the nature and evolution of the first ever light sources. I will give an overview of what has already been done, and what is yet to achieve to get our answers. Despite promising results from the Hydrogen Epoch of Reionisation Array (HERA), which has recently given the lowest upper limits on the 21cm power spectrum at redshifts z > 7, I will show how a first detection of small-scale EoR signatures will likely come from joint analyses and cross-correlations.