Early Galaxies and Reionisation
Group Leader: Anne Hutter
![The evolution of the universe during the first billion years [Image Credit: Anne Hutter]](/fileadmin/_processed_/csm_The_Evolution_of_the_Universe_during_the_First_Billion_Years__Image_Credit_Anne_Hutter__5b58ed9286.png "The evolution of the universe during the first billion years [Image Credit: Anne Hutter]")
The evolution of the universe during the first billion years [Image Credit: Anne Hutter]
The Early Galaxies and Reionisation Group
The first billion years of our Universe marked a transformative period, when the first galaxies emerged as the first sources of light and elements heavier than lithium. Their stars heated and ionised the surrounding intergalactic gas, driving the transitions from a cold, neutral Universe to a warm, ionised one, the Epochs of Heating and Reionisation. Telescopes are now peering deeper into the cosmos, collecting information about these early galaxies and the intergalactic medium. To fully interpret these observations, our group models the formation and evolution of the first galaxies, their impact on the intergalactic medium, and the resulting observables using theoretical models and simulations. Ultimately, we aim to answer questions such as: What were the properties of the first galaxies? What types of stars did they host, and how did these shape their luminosities and chemical enrichment? What imprints did the first galaxies leave on the heating and ionisation of the intergalactic medium, and how can we constrain these properties from observations?
Research Focus
- Models of early galaxy evolution and reionisation: Our group has developed the Astraeus framework, which self-consistently couples a semi-analytic galaxy evolution model with a semi-numerical reionisation scheme, and runs on the outputs of dark matter N-body simulations. We continuously refine Astraeus, improving the modelling of gas processes, star formation, chemical enrichment and spectral emissions to better describe the early Universe.
- Star formation in early galaxies: Astraeus uniquely supports a continuously varying stellar initial mass function (IMF). We explore different parameterisations and dependencies of the IMF, their effects on chemical enrichment and spectra of galaxies, and develop star formation models that better capture the bursty nature of star formation in early galaxies.
- The cosmic 21cm signal: We model the 21cm signal during the Epoch of Reionisation and investigate statistical analyses of the 21cm signal that quantify the ionisation morphology of the intergalactic medium. Our goal is to identify the analyses most sensitive to the properties of the first galaxies and suitable for constraining them with observations.
- Connecting 21cm and galaxy observations: We investigate how combining 21cm signal and galaxy surveys can shed light on the reionisation process. We are especially interested in analyses tracing the ionisation morphology, which provides key insights into the properties of the first galaxies.