Seminars and Colloquia at ESO Garching and on the campus

The new data from the ongoing observing facilities have revolutionized our view of the early Universe, having detected luminous galaxies at unprecedent redshifts. However, the formation and evolution of these objects are still unclear from the theoretical side and has enhanced the urge for data-driven models to bridge the gap between observations and theoretical expectations. Here, I present the results on the stellar mass growth of galaxies from our cosmological semi-empirical model. We simulate galaxy star formation histories via abundance matching using the most up-to-date observed luminosity functions from a wide range of high-z surveys, including JWST and Euclid. Mergers are added by initialising satellites via accurate stellar mass-halo mass relations on top of merger trees from N-body simulations, setting constraints on galaxy merger rates. In this presentation, I will show how our cosmological model can fairly reproduce the observed galaxy abundances with minimal assumptions, and their star formation efficiencies within a LCDM framework. I will also show what are the relative contribution of mergers on the galaxy stellar mass growth against in situ star formation. Finally, I will discuss how mergers can potentially impact the quenching of massive galaxies at the same redshifts and reproduce the observed number densities and fractions of quiescent galaxies.

Stellar population synthesis models implicitly rely on the assumption of a fully sampled initial mass function (IMF). However, with current technological developments pushing towards high angular resolution and ultra deep observations, this assumption does not necessarily hold true. The possibility of an incomplete sampling of the IMF poses therefore a fundamental challenge to all state-of-the art stellar population models currently available. In this talk, I will describe how the same principles and ingredients of the standard evolutionary stellar population synthesis can be naturally combined with a partially sampled IMF. This so-called semi-resolved regime requires profound methodological changes but also offers unique and promising observational opportunities.

Probing the composition of exoplanet atmospheres reveals the physical processes at play and provides insights into their interior and formation history. Atmospheric temperatures are key in shaping these atmospheres and setting molecular abundances. However, warm exoplanets (Teq < 1000 K) are not well understood. JWST opened a new window into these atmospheres thanks to its broad coverage from red to mid-infrared wavelengths and unprecedented sensitivity. Carbon- and sulphur-bearing species are now detected with high significance and their abundances can be measured. In this talk, I will give new insights on the atmospheres of transiting gas giant exoplanets focusing on the warm Neptune WASP-107b, the warm sub-Saturn HAT-P-12b, and the hot Jupiter WASP-43b that has a warm nightside. These studies highlight the importance of processes that alter thermochemical equilibrium and the role of the atmospheric temperature, provide clues on the presence and composition of clouds, but also leaves unanswered questions. I will also present other projects that I conduct with JWST, from the calibration of the MIRI instrument to the search for unknown asteroids.

PDS 70 is the first confirmed multi‑planet system imaged within a protoplanetary disk, but the evolutionary state of its companions depends strongly on the poorly constrained age of the system and its Upper Centaurus–Lupus (UCL) environment. I will present a kinematic approach to this problem using Chronostar, a Bayesian forward‑modelling framework that decomposes stellar populations in six‑dimensional phase space into expanding Gaussian components. Applied to a candidate population associated with the T component of Sco–Cen, our reconstruction identifies PDS 70 as part of an extended, elongated young stellar structure with a membership‑weighted age of approximately 12–15 Myr. I will discuss how this kinematic age compares to other UCL age estimates, and what it implies for the luminosities, masses, and formation scenarios of PDS 70 b and c when combined with planetary cooling tracks and dynamical mass constraints.