Line of research overview

Early Universe and the Epoch of Reionization

Principal Investigator: Valentina D’Odorico

Abstract: The first billion years of the Universe define the current frontier of modern cosmology, both observationally and theoretically. During this time, the first stars and galaxies assembled from the primordial gas, and the atomic hydrogen permeating the early Universe became ionised. The epoch of reionisation (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 (Planck collaboration 2018, arXiv:1807.06209; Kulkarni et al. 2019; Konno et al. 2018; Pentericci et al. 2018) suggest that the EoR was underway at z~9 and lasted below z~6. Thanks to the increasing number of bright quasars detected at z ≥ 6 (e.g. Bañados et al. 2016; Wang et al. 2018 arXiv:1810.11926) it is now possible to pierce into the EoR. High-z bright quasars can be used both as signposts of big massive galaxies, whose properties can be studied in emissions and as background sources to study the intervening medium in absorption along the line of sight. The nature of the first stars (so called PopIII stars), responsible for the reionization process, can be studied both locally, looking for the oldest and most metal-poor stars in our galaxy and in its close companions, and at the highest redshifts, determining the chemical abundances of the absorption systems in quasar spectra. We propose a line of research to investigate these topics using state-of-the-art, multiband observations of high-z quasars and predictions from hydro-dynamical and semi-analytical models.

Status of project and perspectives: Highlights of the activity include:

• In 2019 we were awarded a Large Program of 248 hours with the XSHOOTER spectrograph at the ESO Very Large Telescope to observe 30 QSOs with redshift z~5.8-6.6 to explore the reionization epoch (P.I. V. D’Odorico). This spectroscopic sample, dubbed XQR-30,  has already demonstrated its relevance as a probe of the characterization of the Universe in the second half of the reionization process (see publication list) and we are going to exploit it in the next few years. 
• IFPU Colloquium by Marta Volonteri (IAP, Paris, France) organized in March 2022.
• Cescutti, D’Odorico and Feruglio (plus other members of this line of research) are part of the SOC/LOC of the conference “HACK100: Past, Present and Future of Astrophysical Spectroscopy” organized by INAF-OATs for June 2022 on the occasion of the centenary of Margherita Hack’s birth. The conference will have several invited and contributed talks dedicated to the topics of our line of research. 
• A total of 25h hours of observing time have been obtained with ALMA cycle 7 and 8 on the subject of observations of gas and dust in the first QSOs (PI Feruglio). One paper in advanced stage based on these data (Tripodi, Feruglio, et al. to be submitted). Other observations are ongoing, analysis planned for mid 2022.