Special Colloquium
Daniel Maschmann	SCHEDULED

University of Wyoming, USA

Compact star clusters are gravitationally bound systems that preserve the properties of the interstellar medium where they formed. This makes them ideal probes of past star-formation activities and the mass-assembly history of their host galaxy. With high resolution HST and JWST observations we can identify the star cluster population in nearby galaxies (5-23 Mpc) providing an alternative gateway to study stellar populations. I will present the publicly available PHANGS-HST star cluster catalog consisting of ~100,000 star clusters and compact stellar associations identified in 38 nearby galaxies. I will further discuss their observational and physical properties and include new JWST observations. With this statistical power we were able to find a direct link​ between the star cluster population properties and the host galaxy’s position relative to the main sequence of star-forming galaxies. This confirms that small-scale stellar populations provide a unique window into the global evolution of their hosts. Star cluster samples selected from HST observations are biased towards more evolved star clusters that are no longer deeply dust embedded. New JWST observations including the NIR and MIR at comparable resolution reveal that we are missing a significant amount of ongoing still dusty star formation which is a crucial aspect of the Baryonic Cycle. Furthermore, were we able to identify ongoing dust production in young massive star clusters with JWST that points towards mass-dependent feedback mechanisms. Finally, I would like to discuss future efforts to combine our knowledge of individual aspects of the Baryonic Cycle, including phase transition in the earliest star formation stages and further discuss star-formation triggering.

	Main Colloquium
Prof. Dr. Claudio Ricci	SCHEDULED

Department of Astronomy, University of Geneva, Switzerland

Accreting supermassive black holes can outshine their host galaxies, yet the physical conditions close to these objects remain difficult to measure. One of the least understood regions is the corona, the hot plasma responsible for much of their X-ray emission. How is this plasma heated, what magnetic fields does it contain, and how does it accelerate particles? Recent observations suggest that millimeter emission could provide a complementary way to address these questions, while also helping us find accreting black holes hidden by gas and dust. In my talk, I will present recent results obtained using high-resolution ALMA observations of nearby active galaxies without powerful radio jets. We detect compact millimeter emission in almost all of these systems and find a tight relationship with their X-ray luminosity, suggesting a close connection between the two emitting regions. Our recent work on more luminous, rapidly accreting black holes reveals stronger millimeter emission than expected from this relation, alongside a close connection with the total power radiated by the accretion flow. I will discuss what these results tell us about how the plasma changes as black holes accrete more rapidly. Observations at several millimeter wavelengths, variations on timescales of days, and polarization measurements provide further clues to where the radiation is produced. Combined with physical models, these measurements allow us to test a coronal origin and investigate the size, magnetic fields, and energetic electron population of the emitting plasma. Finally, I will discuss how millimeter observations could reveal black hole growth in systems so heavily obscured that even their X-ray emission is strongly suppressed.