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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.

The EWOCS view of supermassive stellar clusters

Sede A. Riccò Via Santa Sofia 78, Catania

Star formation in our Galaxy typically occurs in environments less massive than 10^4 solar masses. However, a few more extreme star forming environments on the Milky Way exist, where hundreds of thousands to millions of stars form in dense regions. Often called “supermassive star clusters”, they are rare in our Galaxy today, while they are common in galaxies experiencing epochs of starburst. The international project EWOCS (Extendend Westerlund 1 and 2 Open Clusters Survey) is targeting the two closest superstar clusters in the Milky Way with a multi-wavelengtht survey which is based on an extensive set of data from radio to X-rays, with the main objective of studying the formation and early evolution of stars over the whole mass spectrum in a starburst environment.
In this talk, I will discuss the motivations and objectives of the project, the published results, ongoing studies and the future developments.

The Nature of Polarized Sources in the MIGHTEE XMM-LSS Deep Field

Sede A. Riccò Via Santa Sofia 78, Catania

This study explores the polarized emission of the faint extragalactic radio sources in the MIGHTEE (MeerKAT International Giga-Hertz Tiered Extragalactic Exploration, Jarvis et al., 2016) survey in order to systematically study cosmic magnetic fields in galaxies to high redshift. Reaching a sensitivity of 1.5 µJy/beam at a resolution of 5 arcseconds, MIGHTEE is providing an opportunity to chart the evolution of polarized emission from distant galaxies over cosmic time.
The MIGHTEE survey detects polarized emission for a large number of radio sources down to total intensity flux densities of the order of 100 µJy. At these flux densities the source population is increasingly dominated by star-forming galaxies (SFGs) as opposed to active galactic nuclei (AGNs). While polarized emission of AGN can be traced to very distant galaxies, polarized emission of SFGs at moderate distance has been detected only once.
I use multi-wavelength criteria to classify MIGHTEE radio objects as either SFG or AGN. I perform Rotation Measure Synthesis (RMSY) on the spectro-polarimetric data cubes and use the polarization and RMSY spectra to search for polarized emission. A comparative analysis of the polarization properties of SFGs and AGNs is performed. The analysis is extended to the lowest possible flux densities using stacking techniques. I will show preliminary results of the MeerKAT polarization studies of radio sources down to a sensitivity at the micro-Jansky level.