Seminars and Colloquia at ESO Garching and on the campus

Observations of the high-redshift Universe are reshaping our understanding of how the first stars and galaxies formed. In this talk, I will show how the formation of primordial structures can be modelled by linking microphysical processes to cosmological scales and how these predictions compare with the latest observations from ALMA and JWST.
I will present results from ColdSIM, a suite of hydrodynamical simulations that follows the evolution of cold cosmic gas with non-equilibrium atomic and molecular chemistry, radiative cooling, star formation, stellar feedback, and metal enrichment from SNII, AGB stars, and SNIa. These simulations provide self-consistent predictions for galaxy stellar masses, UV luminosities, and the brightest submillimeter cooling lines, including [C II] 158 μm and [O I] 63 and 145 μm.

By combining simulations with recent observations, I will explore the physical properties of galaxies at z > 5, including their HI and H₂ content, star formation rates from Pop III and Pop II-I stars, gas depletion timescales, star formation efficiencies, and mass-metallicity relations. This comparison provides new insights into the physical processes that drove the formation and early evolution of the first cosmic structures.

The field of black hole accretion is seeing a renaissance in the last 5–10 years, thanks to the advent of wide-field, time domain surveys across the electromagnetic spectrum. These surveys monitor hundreds of thousands of AGN at unprecedented cadence, revealing the secrets AGN were keeping while we weren’t watching. Time domain surveys are changing what we thought we understood about standard AGN activity, and thus, evolving our picture of how supermassive black holes grow and affect their environments. In this talk, I will present some recent highlights on supermassive black hole transients, like Tidal Disruption Events, and a new phenomenon called Quasi-Periodic Eruptions, which are a totally unexpected X-ray phenomenon, where ~million solar mass black holes show extremely high-amplitude regular flares, which have been posited as due to the presence of an orbiting stellar mass object (also known as Extreme Mass Ratio Inspirals). We will discuss the current state of the field, and implications for future joint detections with the NewAthena, LISA Gravitational Wave Observatory and other multi-messenger facilities.

Classical and recurrent novae are among the most luminous transients in the Galaxy, powered by a thermonuclear runaway on an accreting white dwarf. Their eruptions probe extreme regimes of nuclear burning, mass ejection, radiative feedback, and shock physics, and they play a relevant role in the Galactic chemical evolution. X-ray emission from novae arises from three different components: the hot white dwarf atmosphere, visible as a super-soft source at the Eddington luminosity for some time after the outburst; the shock-heated plasma within different velocity components of the ejecta; and finally, when the outburst is over, the accretion-powered cataclysmic variable that has hosted the nova event. High-resolution X-ray spectroscopy uniquely constrains white dwarf temperatures and surface composition, while also diagnosing shock velocities, ionization states, and plasma temperatures in the expanding ejecta. Observations to date reveal complex, rapidly evolving spectra that challenge static atmosphere and simple shell models. Recent high-resolution X-ray spectroscopy shows radiative recombination continua (RRC) and signatures of charge exchange (CE)  in the expanding ejecta. At the same time, short-period oscillations detected in the super-soft emission of the post-nova remain a mystery, with their possible scenarios foreseen so far, related to g-mode pulsations or magnetic white dwarfs, both challenging our present understanding of the H-burning process in novae. On the harder X-ray band, shocks in the ejecta probed by X-ray spectroscopy are also responsible for the particle acceleration that powers the VHE detected in many novae. Finally, the effect of the nova outburst itself on the accretion disk and the inter-outburst evolution of the system has been only recently explored thanks to the eROSITA All Sky Survey, confirming the predicted evolution by multi-outburst simulations for the first time.