From the First Stars to the Epoch of Reionization

Principal Investigator: Valentina D’Odorico


  • Early Universe


The first billion years of the Universe define the current frontier of modern observational cosmology. During this time, the first stars and galaxies assembled from the primordial gas, and the atomic hydrogen permeating the early Universe became ionized. The epoch of reionization (EoR) represents a major phase transition in cosmic history, which impacted almost every baryon in the Universe. Recent results from independent, state-of-the-art probes of the reionization process suggest that the reionization process was underway at z~9 and lasted possibly down to z~5.3. New facilities (e.g. JWST) enable new probes of this epoch. Thanks to the increasing number of bright quasars detected at z ≥ 6 it is now possible to investigate the details of the second half of the EoR. High-z bright quasars can be used both as signposts of the most massive galaxies, whose properties can be studied in emission, and as background sources to study the intervening medium in absorption along the line of sight. Studies of galaxies reaching z ≥ 10-12 give us a direct look to the most numerous players in the epoch of reionization. JWST plays a key role in this respect, for the investigation of the assembly and the star formation history of early galaxies.

Finally, the nature of the first stars (so called Pop III stars), can be studied both locally, looking for the oldest and most metal-poor stars in our Galaxy and in its close companions, and at high redshift, through the detection of their nucleosynthetic signature in quasar absorption systems and by direct observations in emission with JWST. Dedicated chemistry/hydrodynamical simulations of primordial epochs are required to understand the drivers of early star formation episodes, the origin of primordial molecules and heavy elements and their impacts on the surrounding medium.

This line of research investigates these topics by combining the expertise of our research team, our direct access to state-of-the-art, multiband observations of local metal poor stars, high-z quasars and galaxies, and predictions from hydro-dynamical and theoretical models.