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Galactic Archaeology: decoding the fossil record of Galaxy formation and evolution

Sede A. Riccò Via Santa Sofia 78, Catania

One of most important issue in Astrophysics is the achievement of a robust understanding of the sequence of processes that contributed to the building up of the Milky Way. This is obviously important not only "on a local scale" in order to recover the history of formation and evolution of the Galaxy, but also, more in general, for understanding the formation process of spiral galaxies. In the last decade, the advent of high precision photometric and spectroscopic surveys as well as the possibility to estimate, thanks to the ESA Gaia mission, accurate distance for a huge number of field stars, combined with the development of an accurate theoretical framework, is actually opening a new era for this kind of investigations.
We will present some recent results - obtained by using this updated observational and theoretical framework - about the formation and early evolution of the Milky Way.

Status and future of 21-cm cosmology during the first billion years

Sede A. Riccò Via Santa Sofia 78, Catania

The 21-cm hyperfine line of neutral hydrogen is set to revolutionize studies of the first billion years, spanning the cosmic dawn of the first stars and eventual reionization of our Universe. I will discuss the potential of this probe in learning about the unknown astrophysics of the first galaxies as well as physical cosmology. Current upper limits on the cosmic 21-cm power spectrum already provide new insights into the heating of the intergalactic medium, and the X-ray sources in the first galaxies. I will discuss the upcoming steps, including the main challenges, that will eventually lead to the Nobel prize-worthy 3D map of half of our observable Universe with the Square Kilometer Array (SKA) telescope.

The Fossil Groups puzzle: ancient relics or young pretenders?

Sede A. Riccò Via Santa Sofia 78, Catania

Fossil groups (FGs) were initially believed to represent the end stage of galaxy group evolution, characterised by a significant luminosity gap between their two brightest member galaxies which was seen as an indicator of their advanced age. In this picture, FGs were thought to undergo a long passive evolution in which their bright satellites gradually merged into the central galaxy, making them fossil relics of the ancient Universe. However, results from the Fossil Group Origins (FOGO) project suggest a paradigm shift: FGs are not necessarily old, but rather isolated systems whose location within the cosmic web primarily regulates their evolution. In this scenario, the magnitude gap arises at low redshift thanks to the infall of galaxies on radial orbits, which enhances the merging rate observed in FGs.

In this seminar, I will review the progress achieved over the last 15 years that led to this new interpretation. I will discuss the luminosity functions, substructures, cosmic web environment, and orbital distribution of FG galaxies, also highlighting the view of FGs as transitional systems. Numerical simulations will also be presented to support the observational evidence, reinforcing the idea that the magnitude gap is a relatively recent feature rather than the imprint of an early formation epoch.