Seminars and Colloquia at ESO Garching and on the campus

In recent years, thousands of exoplanets have been discovered. These are a diverse set of planets that range from rocky and Earth-like to giant gaseous planets much larger than Jupiter. Of these, only a handful have been observed while still embedded in the disks from which they form. This is because directly observing forming planets is difficult. Not only are these objects faint and close to their young stellar host, but also the disk emission complicates many of the traditional techniques for separating the various bright components in order to isolate the planetary signal. In this talk, I will discuss the use of infrared aperture masking interferometry with VLT/SPHERE and JWST to observe the cavities of transition disks at separations beyond the capabilities of traditional direct imaging methods. I will discuss the use of a joint Bayesian modelling approach to fit for the dominant disk emission and simultaneously recover any point-like planet signal. I will discuss the results of applying this approach to ground-based data of LkCa 15 and HD 100546, as well as the first space-based interferometric detection of exoplanets, PDS 70 b and c.

On their way from the main sequence to the final supernova explosion, massive stars lose a substantial fraction of their mass through line-driven winds. Recent decades have witnessed significant advancements in both observational and theoretical studies of these winds that sail on starlight. The advancements in our understanding of radiative driving lead to progressively more accurate estimates of mass-loss rates from massive stars. In this talk, we will outline the key ingredients necessary for reliable predictions of mass-loss rates from numerical simulations, and demonstrate how state-of-the-art theoretical mass-loss rate estimates compare with observational results.

Wolf-Rayet stars (WRs) are the penultimate evolutionary stage for stars more massive than 25-40 Msun, and are considered immediate progenitors of stellar mass black holes. The formation of WRs through single or binary stellar evolution channel is a debated topic, and the contribution of the two channels is uncertain. To get more insights into this, spectroscopic studies have attempted to determine the multiplicity of WRs, but are largely limited to relatively high mass ratios and short periods. In this talk, I will discuss a complementary approach to this problem with infrared interferometry and highlight the key discoveries and limitations of this method.

It is creativity/novelty that drives scientific breakthroughs and societal progress, but the journey from a novel scientific idea to a practical solution can be long and winding. Debates also persist regarding whether and how science contributes to practical solutions. In his talk, Jian will explore the complex relationship between novelty and impact in science and technological innovation. Furthermore, he will examine concerns that the current science funding system is increasingly risk-averse and favours short-term, safe projects over long-term, risky and novel projects. He will also present empirical evidence about whether major funding agencies are biased against novelty in their project selection process, and whether receiving funding enables grantees to engage more in novel research. Finally, he will discuss strategies that scientists can use to boost creativity, such as how to structure the professor-PhD student relationship, collaboration teams, and broader collaboration networks.

You can find the abstract and a short bio by the speaker at:

https://indico.euro-fusion.org/event/2559/page/18-highlight-topic-creativity-in-science

The abundance of massive halos (and of the galaxy clusters they host) has long been recognized as an extremely promising probe of the large-scale structure of the universe. Over the past decade, tremendous progress was made, notably thanks to the availability of high-resolution surveys of the Cosmic Microwave Background (CMB), of high-quality measurements of gravitational lensing, and of advanced numerical simulations.

The sample of galaxy clusters selected by the South Pole Telescope (SPT) in the CMB now exceeds a thousand objects. The Dark Energy Survey (DES) allows for measurements of gravitational lensing for almost 700 sample clusters with exquisit control over systematic uncertainties. We supplement this dataset with 39 lensing measurements of high-redshift clusters with the Hubble Space Telescope (HST). The joint analysis of the cluster abundance and weak-lensing mass calibration provides tight cosmological constraints that are competitive with other major probes.

In my talk, I will review the SPT cluster cosmology and mass calibration program. I will focus on the latest SPT + DES Y3 + HST analysis and present new cosmological constraints.

High resolution, hydrodynamic galaxy simulations can be used to investigate the inherent variation of dark matter around the Solar Circle of a Milky Way-type galaxy. These simulations self consistently include both the baryonic back-reaction as well as assembly history of substructures, all of which may have lasting impacts on the dark matter’s spatial and velocity distributions, creating `gusts’ of dark matter wind around the Solar Circle, potentially complicating interpretations of direct detection experiments on Earth. Direct detection is a key experimental goal to advance the microscopic understanding of the dark matter that fills the Universe. We investigate how dark matter substructure, simulated in halos analogous to our own Milky Way, impacts the shape, summary statistics, and interpretation of results from terrestrial dark matter direct detectors.

Implementing a new numerical integration technique, our work generates bespoke predictions for terrestrial underground detection, finding large uncertainties arising in the expected signals of direct detection experiments. Having developed a realistic end-to-end pipeline for studying these effects, we discuss the implications of these astrophysical variations in the dark matter distribution of the solar neighbourhood on current and future particle physics searches for dark matter.

Driven by gravity, galaxies continuously grow through accretion of smaller systems. Stellar streams are nice illustrations of this hierarchical build-up, but the accreted stars quickly disperse. I will present advanced dynamical models that can convert the observed positions and velocities of stars to phase-space quantities like energy and angular momentum which remain largely conserved. In addition, these models can include the observed ages and chemical properties of stars which are also conserved. The resulting population-dynamical models allow us then to uncover even those accretion events which are now fully dispersed. At the same time, these models also accurately constrain the total mass distribution, including a central black hole and dark matter halo.

I will illustrate how these models make optimally use of observations to unveil the dark side and colour past of galaxies: from accurate measurements of their central black holes and extended dark halos, to unveiling the formation history of their disks, to uncovering ancient massive mergers and accreted satellite galaxies. By the end, I aim to have demonstrated that these models provide a unique bridge between the studies of resolved stars in the Milky Way and integrated-light of high(er)-redshift galaxies. Together with direct coupling to state-of-the-art galaxy formation simulations, these population-dynamical models enable us to uncover the hierarchical build-up of galaxies in a cosmological context.

Ultra-diffuse galaxies (UDGs) are extremely low-surface brightness galaxies with a size of several kpc, i.e. comparable to that of the Milky Way, but with at least 100 times smaller stellar masses. In the scope of the LEWIS large programme with VLT-MUSE, we have targeted a complete sample of 32 UDG candidates in the 50-Mpc distant Hydra I cluster. In this talk, I will focus on UDG 32, a galaxy that has been hypothesised to have formed from material stripped from the nearby spiral galaxy NGC 3314a. Our new MUSE data show that NGC 3314a's filaments extend to unprecedented distances, completely engulfing the UDG and confirm that the UDG and the filaments are indeed co-spatial based in position-velocity space. UDG 32 may thus be one of the first ultra-diffuse galaxies where we catch the formation from ram-pressure stripped gas in the act.

The Central Molecular Zone (CMZ) is an extreme environment in the inner few hundred parsecs of the Milky Way Galaxy, with temperatures, pressures, and densities exceeding those measured in the Galactic disk. At a distance of ~8.2 kpc, it has previously been difficult to perform large surveys of the CMZ at high resolution, limiting most studies to individual molecular clouds. ACES (the ALMA CMZ Exploration Survey) is a large ALMA program with high sensitivity observations covering the entire area of the CMZ at high spatial and spectral resolution at 3mm in both continuum and spectral lines. ACES data will be used to determine the overall distribution and chemical composition of mass in the inner Galaxy, from the sub-parsec scales of star formation, to the large-scale global processes that influence it. In addition, spectral line data will be used to create a comprehensive picture of gas kinematics in the CMZ, unveiling how gas flows from galactocentric radii of a few hundred pc down to the vicinity of the central supermassive black hole. Observations and high resolution hydrodynamical simulations will be used in tandem to determine how different physical processes impact the evolution of gas at different scales. We present early science results from the ACES team, including an overview of the data products, the properties of compact sources extracted using ACES continuum data, the rich chemical composition identified in the CMZ, and the characterization of gas kinematics in the CMZ.