Abstract

For decades, the entire electromagnetic spectrum of the recent Universe has been intensively studied by powerful ground and space telescopes. Besides, its birth is also relatively well known thanks to the detection and characterisation of the Cosmic Microwave Background. However, the period in between during which the first structures of the Universe started to emerge remains mysterious. Indeed, following the emission of the CMB , the universe was dark and mainly filled with neutral hydrogen, until the very first stars and galaxies form and ionize the gas in the intergalactic medium. Unfortunately, the emitted light is too faint and so cannot be directly observed with the current instruments. Studying the early Universe is yet fundamental to understand the conditions of its origin, evolution, and therefore its present state. In order to complete our knowledge of the history of the Universe, the University of Cambridge is closely involved in the design and development of two super radio-telescopes: HERA and the SKA , respectively built in the deserts of South Africa and Australia. These two radio-interferometers will probe the early Universe between 115 million and 1.3 billion years after the Big Bang for HERA , and even up to 2.1 billion years for the SKA low frequency array. But instead of trying to directly observe the first galaxies, they will infer information about their characteristics (size, formation rate…) by measuring the evolution of the distribution of the neutral hydrogen which interacts with the surrounding galaxies. In this talk, I will give an overview of these two radio-telescopes, and explain more in details how, hopefully, they will reveal the mysteries of the early Universe.