Dottorato - PhD thesis
Area Tematica: RSN 1: Galassie e Cosmologia
Referente: Valentina D'Odorico, (
Titolo: Metal enrichment of the intergalactic medium and the nature of the first ionizing sources
Progetto: ERC Synergy Grant "RECAP"
Decorrenza: 24.04.2025
A few hundred million years after the Big Bang, the Universe was a cold and dark place, filled with neutral hydrogen. The first stars and galaxies that formed began to carve out ionized bubbles around them through the emission of photons with energies greater than 13.6 eV. At the same time, these early sources expelled some of the metals produced in stellar interiors, enriching the surrounding medium. This marked the beginning of the reionization of the Universe. The heavy elements released during this early epoch are expected to be found in the low-density gas near the cosmic mean density—known as the intergalactic medium (IGM). By comparing the observed distribution and abundance of these metals with theoretical predictions, we can infer key properties of the first ionizing sources. Observationally, the low-density IGM is studied via absorption features imprinted in the spectra of bright background sources, primarily quasars. However, only a limited number of quasar spectra currently have the spectral resolution and signal-to-noise ratio necessary for these measurements. This PhD project aims to determine the metallicity of the IGM using a statistical sample of new, very high-resolution and high signal-to-noise quasar spectra in the redshift range z ~ 3.5–4.5. The student will apply both direct line detection methods and statistical techniques designed to measure the cumulative metal content of the IGM. These observational results will be compared with predictions from state-of-the-art simulations and semi-analytical models. The ultimate goals of the project are to assess the presence of metals in the IGM, quantify their abundance, evaluate their contribution to the total metal budget at high redshift, and, through comparison with simulations, infer the general properties of the first ionizing sources. The project is funded by the ERC Synergy Grant “RECAP,” for which Valentina D’Odorico is one of the four international coordinators. The PhD student will work within an international collaboration, with opportunities for frequent visits to partner institutions and extensive interaction with a large group of researchers working together to answer fundamental questions about the epoch of Reionization.
