How and when the Universe warmed up (and what that means for learning about dark matter)

One of the most important questions in astrophysics is what is the invisible “dark” matter that accounts for most of the matter in our Universe? One method of learning about the nature of dark matter is by studying the properties of diffuse intergalactic gas in the early Universe. However, the temperature of this intergalactic gas is a major uncertainty, as hotter gas can mimic the observables of some dark matter models. In this talk, I will discuss what is known about the thermal history of intergalactic gas across the first billion years of the Universe. This is an especially interesting time in the history of the Universe, as it coincides with the formation of the first stars and galaxies, which are thought to be responsible for heating the Universe through the emission of hard UV photons. I will describe my work using cosmological simulations to model how the Universe was heated up by the first galaxies, and how this impacts the properties of the intergalactic gas. I will show how a better understanding of this heating process could improve our constraints on dark matter models.