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The nature of the first galaxies and reionisation: challenges in the era of SKA, Roman and JWST

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The nature of the first galaxies driving the reionisation of the intergalactic medium (IGM) and their imprint in the ionisation state of the intergalactic hydrogen gas remain outstanding questions in current astrophysics. With the upcoming launch of the James Webb Space Telescope (JWST), the Nancy Grace Roman Space Telescope (Roman), and the Square Kilometre Array (SKA), a vast amount of data will be collected that will revolutionise our understanding of the first galaxies. The number of detected early galaxies will increase greatly, and the 21cm signal from the neutral hydrogen in the IGM will probe the ionised regions continuously growing around the first galaxies in time and space. Semi-analytic models as well as semi-numerical and numerical simulations provide a great avenue to understand the characteristic signatures of galactic processes in these forthcoming galaxy and 21cm signal (IGM) observations during the Epoch of Reionisation. In this context we have developed the Astraeus framework. Astraeus contains a large (230 Mpc box) and highly resolved simulation that couples a semi-analytic model of early galaxy evolution with a semi-numerical reionisation scheme self-consistently. I will introduce this model and use it to discuss how radiative feedback from reionisation and the escape fraction of HI ionising photons from galaxies leave traces in the light emitted by the galaxies and the 21cm signal. I will end by explaining how synergising galaxy and 21cm observables can constrain the reionisation process.

This talk is part of the Galaxies Discussion Group series.

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