Inferring properties of the first galaxies and intergalactic medium with 21-cm cosmology

Abstract:

The redshifted 21-cm signal provides a unique probe of the first galaxies and their imprint on the thermal and ionization state of the intergalactic medium (IGM) during the Cosmic Dawn and Epoch of Reionization. In this talk, I present a unified inference framework that jointly interprets constraints from low-frequency interferometers (e.g., HERA and MWA) and global-signal experiments such as EDGES, in combination with complementary galaxy and CMB observations.

By jointly modelling these datasets, we find converging evidence that the IGM was heated early, ruling out a broad class of cold reionization scenarios and placing new constraints on the X-ray emissivity of the first galaxies. Within a galaxy-driven framework, these results imply enhanced high-redshift X-ray production relative to local scaling relations, potentially driven by metal-poor stellar populations and their remnants. In parallel, global-signal analyses provide independent constraints on the timing and amplitude of the cosmic dawn signal, and serve as a critical test of its astrophysical interpretation.

As these early sources are likely beyond the reach of direct detection, even for facilities such as JWST, the 21-cm signal remains a uniquely powerful probe of their collective impact. Looking ahead, I will show how the Square Kilometre Array (SKA) will transform this field, enabling precision constraints on the thermal history of the IGM and the properties of the first galaxies.

Please note that the event timezone is AWST (UTC+8 hrs)

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