Events, Seminars, Talks

Abstract
Galaxy clusters, representing the peaks in the cosmic density field, serve as an independent and powerful tool for investigating the evolution of cosmic structures. The strategic identification of these clusters through multi-wavelength surveys is essential for advancing our understanding of gravitational theory, general relativity, and cosmological models. Launched in 2019 aboard the Spectrum-RG mission, eROSITA marked a major milestone in astronomy by enabling the construction of the largest pure sample of galaxy clusters and groups detected through their hot intra-cluster medium in the X-ray band. In this talk, I will present results from my group’s work on deriving cosmological constraints from the evolution of the cluster mass function, combining eROSITA data with optical surveys such as DESI Legacy, DES, HSC, and KIDS. These parameters are constrained at a percentage level through the evolution of the cluster mass function, representing a significant leap forward. Beyond cosmology, a central focus of my research is on AGN feedback and its role in shaping galaxy and structure formation. Leveraging the statistical power of the eROSITA sample, we have detected warm baryons within cosmic filaments and cluster outskirts, offering a first glimpse of baryons in the faint, diffuse cosmic web. To arrange a visit with the speaker during the visit, please contact their host: Matteo Maturi

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The lives of galaxies are governed by the accretion of gas, its consumption via star formation, its removal or heating through feedback, and environmental effects. In recent years, the James Webb Space Telescope (JWST) has unveiled an unexpectedly high density of massive quiescent galaxies at high redshift , challenging standard models of early galaxy growth. Cosmological simulations predict that these quenched systems preferentially live in dense regions, where they experience accelerated growth and more feedback from Active Galactic Nuclei (AGN). Observationally, clustered environments indeed exhibit enhanced AGN activity, and AGN feedback is increasingly viewed as the primary driver of quenching in massive galaxies. In this talk, I will present JWST/NIRISS slitless spectroscopic observations of a merging protocluster at z=3 that simultaneously hosts two quiescent galaxies and a luminous, starbursting quasar at its centre. I will discuss the kinematics, substructure, and halo properties of the system, as well as examine its evolutionary stage and AGN incidence. The central quasar is an example of the rare and intense “extremely red quasar” phase: a luminous and dusty population thought to constitute an early break-out stage, with ionised outflows reaching thousands of km/s - the most extreme warm winds known to date. Spatially resolved observations with JWST/NIRSpec offer a detailed view on gas dynamics, mass loading, and localised physical conditions, bridging the extended environment down to the nucleus. At low redshifts, I will focus instead on a population of AGN with low-velocity ionised outflows and suppressed star formation, which may represent a later phase of feedback. New spatially resolved molecular gas measurements with NOEMA enable a detailed kinematic comparison of cold and warm gas phases, and reveal how the outflows reshape the cold gas reservoir while regulating star formation efficiency. Together, these results showcase distinct examples of how AGN feedback can manifest across different cosmic times and environments.

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KoCo Signature Speaker (GC)

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KoCo Signature Speaker (GC)

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Gaia, developed and operated by the European Space Agency, was launched in 2013, and operated until January 2025. It's creating a revolutionary six-dimensional map of our Galaxy by measuring the accurate distances and space motions of some three billion stars. While the measurement of star positions has a very long history, stretching back more than 2000 years, Gaia's accuracies exploit the numerous advantages of measurements made from above the Earth's atmosphere. Absolute positional accuracies of order 10 micro-arcsec can register stellar motions that would require more than 10,000 years to be discerned on the ground.  This is providing a major advance in understanding stellar evolution, and in unravelling the composition, structure, and history of our Galaxy's formation. I will not focus on the technical details, but provide a "big picture" of Gaia's scientific advances.

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