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Challenges for the forthcoming CMB polarization experiments

Sede A. Riccò Via Santa Sofia 78, Catania

One of the major challenges in the context of the Cosmic Microwave Background (CMB) radiation is to detect a polarization pattern, the so called B-modes of CMB polarization, that are thought to be directly linked to the space-time fluctuations present in the Universe at the very first instants of life. To date, several challenges have prevented to detect the B-modes partly because of the lower sensitivity of the detectors. Our own Galaxy is observed in this context as a foreground contamination. However the awareness of improving the modeling of its polarized emission has been constantly increase not only to assess the cosmological signals but also to provide new insights onto the Galactic magnetic field probed with the Galactic polarized emissions, e.g. synchrotron and thermal dust. This is particularly relevant in order to better characterize the foreground contamination for future CMB experiments (e.g. SO, LiteBIRD, CMB-S4 ), where unprecedented polarization sensitivities are expected to be achieved in the coming decades.

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.