Understanding the first galaxies

IAP weekly specialised seminars / 10 October 2025

Joe Lewis ( Institut d'Astrophysique de Paris & CEA (Paris, France))

The James Webb Space Telescope has ushered in a new era for the study of the first galaxies. Yet, at the furthest epochs, the faintest but most abundant galaxies remain extremely difficult to constrain, motivating the search for indirect ways of determining their nature. One indirect probe of the first galaxies is Reionization. However, interpreting observations of the intergalactic medium (including upcoming high-redshift 21cm observations) requires a thorough theoretical understanding.
At the same time, new observations of unexpectedly luminous high redshift (z≥10) galaxies continue to challenge our theoretical models of galaxy formation. For instance, a number of these early galaxies are already quenched by z=7, which cosmological simulations fail to explain.
In this talk, I will highlight various numerical projects that investigate these issues. First, I will show how simulations can help up better understand how the first galaxies reionize the Universe, and interpret the correlation between galaxy observations and the intergalactic medium. Second, I will explore the relationship between forming early massive black holes and quenching massive high-redshift galaxies, and how simulations could help us better appreciate observational biases in constraints on quenching.