Seminars and Colloquia at ESO Garching and on the campus

Cosmic dust and Polycyclic Aromatic Hydrocarbons (PAHs) account for less than 1% of the interstellar medium by mass, yet they shape the observability of galaxies. Modeling them self-consistently in cosmological simulations of galaxy evolution is one of the main challenges in the ALMA and JWST era.

After introducing the main strategies to model the evolution of galaxies and their dust content, I will present the first cosmological galaxy formation simulation to jointly follow the evolution of the physical grain size distribution and the luminous properties of PAHs across a large volume and cosmic time. I will show how the PAH–metallicity relation emerges naturally from grain shattering in the ISM, and how PAH emission can be used to trace physical properties of galaxies such as star formation rate and molecular gas content. These results provide a physical framework to interpret recent JWST observations at cosmic noon and will help guide future missions such as PRIMA.

PLANETES may replace the PIONIER instrument at Paranal in 2028. This project is part of the Tech-Dev programme and is financed by an ERC grant. The ERC goal is to detect exoplanets in reflected light. The Tech-Dev goals are to test new technologies — new detectors, new metrology concepts, shorter operating wavelengths — in order to accelerate the development of the next generation of VLTI instruments. We will discuss the goals and challenges of the project. In case of success, PLANETES could also be offered to the community as a new VLTI instrument.

The Cold Dark Matter (CDM) paradigm remains the most successful framework for describing the formation and evolution of cosmic structure, yet its predictions on sub-galactic scales are still only weakly tested. A key prediction of CDM is the existence of a large population of low-mass dark matter haloes with a well-defined mass density profile, both as subhaloes within galaxies and as isolated structures along the line of sight. 

Since the majority of these objects are expected to be completely dark, strong gravitational lensing provides a unique opportunity to study them and to probe the nature of dark matter. 

In this talk, I will review the current status of the field and present the latest observational constraints from strong-lensing studies. Recent advances have pushed strong lensing into a previously inaccessible regime of halo mass and physical scale. In particular, Powell et al. (2025) reported the detection of a dark perturber with an enclosed mass of only 10^6M_sun identified through its effect on an exceptionally thin lensed arc observed with milli-arcsecond-resolution VLBI. This represents the lowest-mass object detected at cosmological distance through its gravitational influence and demonstrates, for the first time, that strong lensing can directly probe the million-solar-mass regime beyond the Local Group.

I will also present the latest constraints on the internal structure of the three currently known low-mass detections and show how their inferred properties compare with predictions from different dark matter models. I will then focus on the expected role of existing and upcoming observing facilities such as Euclid, ELTs, SKA, and the ngVLA in this field.

The structure and evolution of the interstellar medium (ISM) strongly dictate galactic gas dynamics, star formation (SF), and galaxy evolution. While recent studies emphasize the rapid formation and destruction of molecular structures by stellar feedback, this conflicts with the observed deficiency of HI gas expected from such destruction. Here, I revisit the alternative paradigm: that molecular structures survive long-term and evolve primarily via galactic dynamics. Using ALMA observations of M83 and 12 nearby galaxies from the FACTS survey, I show that molecular cloud properties evolve alongside large-scale galactic structures. This is supported by correlations between environment, CO 2–1/1–0 line ratios, and cloud boundedness. Crucially, stellar feedback enhances CO ratios only near HII regions and fails to increase velocity dispersions, implying limited feedback-driven turbulence. Instead of undergoing rapid destruction, molecular clouds persist, coagulating and fragmenting via galactic dynamical processes. This framework shifts SF theory from the collapse of diffuse gas toward identifying triggers within long-lived clouds, potentially redefining galactic dynamics as a system governed by the motion of more discrete molecular structures rather than pure hydrodynamics.