Seminars and Colloquia at ESO Garching and on the campus

The European Space Agency's Gaia space mission, launched in 2013, is designed to measure the brightnesses, colors, positions, distances, and motions (in three dimensions) of almost two billion of the Milky Way's hundred billion stars. These measurements are yielding new insights about the internal structure and formation history of the Milky Way, thanks in part to a series of increasingly comprehensive data releases that any member of the astronomical community can access. In this talk, I will introduce the Gaia mission and summarize the latest data release, Gaia DR3. This discussion will be complemented by highlights of the science results from the Gaia data releases, showcasing among others the impact of Gaia on solar system studies, the Milky Way's accretion and recent dynamical histories, and understanding matter in extreme states. I will conclude will a look ahead at the GaiaNIR mission.

Understanding the processes that regulate star formation in galaxies remains at the heart of modern extra-galactic astronomy, and debate continues as to why some galaxies exhibit powerful starbursts whilst others are largely dormant.  The key to progress in this arena lies with assembling large, diverse samples of galaxies for which we can measure all of the critical ingredients, such as the current star formation rate (SFR) and gas content.  However, it is insufficient to simply measure global galactic quantities, as we know that a given galaxy will manifest considerable internal diversity in its star formation activity.  It is therefore essential to study gas and star formation on spatially resolved scales.  The ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey combines maps of stellar properties obtained from the MaNGA (optical) integral field unit survey with ALMA CO (1-0) maps on a common kpc-scale grid, in order to tackle questions of star formation in local galaxies.  The 46 galaxies in the ALMaQUEST sample span a wide range of SFRs, including both normal star forming galaxies, as well as those both on their way to quenching, and those undergoing starbursts.  In this talk, I will present the ALMaQUEST view of understanding the interplay of gas and star formation across this broad galactic landscape.

Massive stars are fascinating objects that are still poorly understood.  Yet, they play a central role in many topical questions in astrophysics. These range from questions about enrichment and feedback in distant galaxies where they dominate the light (now probed by JWST), to questions about their violent deaths given rise to diverse transient (soon to be probed by the Rubin observatory), to questions about the compact remnants they leave behind (now detected through gravitational waves).  In this seminar, I will provide a general introduction and show examples of work by early career researchers that have been active in our group.  With this, I hope to share a taste of the excitement about recent insights, with the appropriate humbleness for the physical processes we still do not understand.

This is a story about how machine learning is enabling us to do bigger, bolder, and more robust Bayesian analyses.

Inferring the properties of the galaxy population in the Universe over cosmic time is of central importance in extragalactic astronomy, both for understanding galaxy evolution, and for enabling us to constrain cosmology and fundamental physics from large-scale structure (via weak lensing and galaxy clustering measurements). The task at hand sounds simple: given an observed galaxy catalogue of measured photometry or spectra, how do we constrain the redshift-evolving properties of the galaxy population? As it happens, this is a really hard problem for a few reasons: (1) parameterising the galaxy population so that it fully encompasses galaxy evolution phenomenology is really hard, (2) the stellar population synthesis (SPS) models relating galaxy physical properties to their observables (spectra and photometry) are too expensive to run at scale for millions of galaxies, (3) both photometric and spectroscopic data have non-trivial data-calibration effects that need carefully accounting for, and finally, (4) even if you could solve 1-3, galaxy surveys are always subject to selection effects, making the likelihood function intractable, so none of the standard Bayesian methodology is applicable anyway. In this talk I will show you how, enabled by recent advances in machine learning, we can now do the galaxy-survey analyses of our dreams: full Bayesian hierarchical analysis, with all the gore.
 

The Sun is often used as a standard for studying low-mass stars. We have more data on the Sun than we can ever hope to obtain for other stars. These data have allowed us to determine the internal structure of the Sun with great precision, which has allowed us to test the theory of stellar structure and evolution and test physical processes. The multi-decade helioseismic data sets also allow us to study changes in the Sun.

In this talk, I shall describe how seismic data have allowed us to use the Sun as a laboratory to study physical processes as well as fundamental properties of matter. I shall also describe how the Sun changes over the solar activity cycle and how the changes are posing challenges to theory.

In this colloquium, I will discuss the aims and current status of research on exoplanet atmospheres. In particular the focus will be on ground-based techniques and results. I will also discuss the first isotope measurements in exoplanet atmospheres and what they may tell us of planet formation and evolution. The ELT provides extremely exciting prospects.

Dust attenuation will be key for interpreting high redshift galaxies observed by HST+JWST, yet the connection between the amount of stellar light lost to dust in the UV-optical and the dust emission recovered in the IR, while being perfectly understood theoretically, is still ill quantified observationally. Much of the ambiguity stems from the degeneracy between the effects of dust attenuation and the ageing of stellar populations on the observed spectral energy distributions of galaxies. When joined with line-of-sight effects from the patchy dust distribution in galaxies, this degeneracy prevents the derivation of general dust attenuation curves for use on the spectral energy distributions of high redshift galaxies. During this talk, I will attempt to briefly summarize the current state of this area of study and propose directions for future progress.

The origin of stellar masses, arguably the most central question in star formation remains a major open issue in modern astrophysics (see review by, e.g., Ballesteros-Paredes et al. 2020). The main goal of the ALMA-IMF Large Program (PIs Motte, Ginsburg, Louvet, & Sanhueza) is to determine how the origin of the initial mass function (IMF) is in fact dependent on cloud characteristics or not. Thanks to its unmatched angular resolution, sensitivity, image quality, and excellent frequency coverage, we used ALMA to survey 15 massive protoclusters, covering a wide variety of Galactic environments and evolutionary stages (Motte et al. 2022). I will present recent ALMA-IMF results (Motte et al. 2018a; Pouteau2022; Nony et al. subm.; Louvet et al. in prep.) that show that the mass distributions of the >600 detected cores (CMFs) in these typical yet extreme environments of the Milky Way present an excess of high-mass cores with respect to the canonical IMF (e.g., Kroupa et al. 2013). A detailed study of two contiguous protoclusters, W43-MM2 and W43-MM3, which are at different evolutionary stages suggests that the CMF deviates from the canonical IMF form when and where a burst of star formation develops (Pouteau et al. subm.). The CMF would thus strongly depend on environmental parameters and may lead to non-universal stellar IMFs and heterogenous, potentially mass-segregated spatial distribution of stars.

In addition, the ALMA-IMF Large Program aims to discriminate between the quasi-static and dynamic scenarios by quantifying the role of cloud and core kinematics in defining core mass and in how this changes over time. I will present initial results on the dynamical properties of cores using the DCN line emission along with the gas kinematics extracted from the dense gas tracer N2H+. ALMA-IMF also provides the community with an unprecedented database (Ginsburg et al. 2022; Cunningham et al. in prep.) with high legacy value for protocluster clouds (60 pc2 at 2000 AU resolution), cores (about 1500 cores with 0.15-250 Msun masses), many of which are associated with outflows, filaments (hundreds of star-forming filaments), often tracing gas inflows, and hot cores (several tens of hot cores).

Star formation and planet formation are genuinely intervowen processes. This tight interconnection largely occurs through the formation of circumstellar and protoplanetary disks. While it has since long been recognised that disks would naturally be explained by the conservation of angular momentum during the collapse of the dense core, several teams have recently stressed, that  due to  efficient magnetic braking, magnetic field is likely playing a crucial role regarding the formation of disks. How this exactly occurs, has however turned out to be rather complicated. This is because on the one hand, magnetic braking has been found to depend on the dynamical state of the collapsing dense core, namely the geometry and intensity of the magnetic field but also the strength of the turbulence. On the other hand, the efficiency of magnetic braking also depends on the ionisation degree and on the charge carriers, the dust grains. None of these processes are really well understood.

During the talk, I will review the subject discussing various simulations, as well as analytical efforts, which have been performed along the years to decipher the respective influence of physics and initial conditions. This goes from highly idealised isolated dense cores to massive clusters. I will also present comparisons between observations and simulations. Finally, I will discuss two important issues, the strong dependence of disk properties in the numerical scheme, namely the sink particles and the possible high level of ionisation seemingly measured within a few dense cores.

Star formation in our Galaxy typically occurs in low and intermediate-mass environments counting a few 10^2, 10^3 stars. However, a few more extreme star forming environments exist, where hundreds of thousands to millions of stars form in dense regions, often in single events of star formation. Often called “starburst regions”, they are quite rare in our Galaxy today, with a few examples known, while they are common in galaxies experiencing epochs of intense star formation activity (such as interacting galaxies) and in the early Universe.

With a distance of 3.87 kpc from the Sun, and an estimated initial mass of 52000 solar masses, Westerlund 1 is the closest starburst cluster to the Sun. It offers the unique possibility to study star and planet formation, the early stellar evolution and the physics of compact objects in a starburst environment.

In this talk I will present the EWOCS project (Extended Westerlund One Chandra, and JWST, Survey) which is based on a 1Msec Chandra/ACIS-I Large Project, oncoming JWST observations of Westerlund 1, and other data at high spatial resolution (GEMS/GSAOI, HST, etc..). I will discuss the objectives of the project and present the status of the art of data analysis.

The Antikythera Mechanism is the first computer in human history. Built during the 2nd century BC, it was retrieved in 1901 from an ancient shipwreck and is nowadays partially preserved in 82 petrified and fragile fragments. Its functions and use remained a mystery until recently. With the use of innovative techniques, we now know that it was a mechanical model of the cosmos, an advanced machine that displayed the position of the Sun, the Moon and the five naked-eye planets on the sky. The recently formed solar, lunar and first planetary theories of ancient greek astronomy were converted into elaborate axles and gears that calculated the exact positions of the celestial bodies. To its basic function, many more had been added, such as a lunisolar and an astronomical calendar and the prediction of eclipses, resulting in a highly complex machine, fully covered with dials, pointers and texts. The Antikythera Mechanism is nowadays the unique preserved artefact of the technical sophistication that these models of the cosmos finally reached.

Analysis of cosmological survey data is challenging for a host of reasons; post-CMB the fields are not gaussian random fields, and we don’t have a good handle on their statistical properties, so how can we do science?   We can make summary statistics (power spectra, correlation functions etc) and assume their distributions, or more ambitiously build a complete Bayesian hierarchical model for the data.  In this talk I will show three different BHMs for cosmology, Almanac (which characterises the statistical properties of cosmic shear data), BORG-WL (which infers cosmology and the initial conditions of the Universe), and a BHM for the redshift distribution of broad-band photometric surveys, and present a re-analysis of the KiDS 450 data with Bayesian redshift distributions.

We present a new solution for the steady state distribution of stars around a supermassive black hole. This solution includes segregation of different masses and clarifies concepts of constant flux vs zero flux, which were a source of confusion in the past.

We apply this solution to (i) discuss the innermost part of our own galaxy, giving prediction to the number of stars in short period orbits (ii) show that galactic centers will be a dominant source for LISA at 10^-3 Hz, (iii) discuss a possible model for Quasi periodic eruptions from main sequence stars, that is consistent with the observed event rate.

The Galactic halo is criss-crossed by long stellar streams that are probably the remnants of defunct globular clusters and dwarf galaxies. I will present the recent discoveries of these structures from Gaia mission data, and provide a lightning tour of some of the highlights.

While streams clearly inform us in a direct way about past accretions onto our Galaxy, perhaps their most promising property is that they allow us to probe the dynamics and past structure of the Milky Way. I will present our work on a novel machine learning technique to measure the local and globa acceleration field and how it changes through time.

The past few years have seen at least six major new radio telescopes come into operation around the world. They incorporate new technologies and processing techniques that have enabled revolutionary advances in sensitivity, frequency coverage and field of view. I will provide an update from one of these telescopes - ASKAP, a wide-field radio telescope operating in a remote region of Western Australia. The main focus of the talk will be on recent science results from ASKAP in two areas: 21cm neutral hydrogen (HI) absorption in galaxies at intermediate redshift; and Fast Radio Bursts (FRBs) and their host galaxies. I will also mention some of the optical follow-up studies being carried out with ESO telescopes, as well as describing the recently-completed Rapid ASKAP Continuum Survey (RACS) which provides a new resource for a wide range of multi-wavelength studies.

Stars are fossils that retain the history of their host galaxies. Elements heavier than helium are created inside stars and are ejected when they die. Elements heavier than iron (such as gold) are also produced by neutron star mergers. From the spatial distribution of elements in galaxies, it is therefore possible to constrain star formation and chemical enrichment histories of the galaxies. This approach, Galactic Archaeology, has been popularly used for our Milky Way Galaxy with a vast amount of data from Gaia and multi-object spectrographs. This approach can also be applied to external galaxies thanks to integral field spectrographs. Theoretical predictions are also available including incorporating detailed chemical enrichment in hydrodynamical simulations from cosmological initial conditions. At all redshifts (z<5) massive galaxies are more metal-rich than low-mass galaxies following the mass-metallicity relations, and the central parts of galaxies are more metal-rich than the outskirts producing metallicity radial gradients. These predictions will be compared and tested with recent and future observations such as with ALMA and JWST.

Scenarios of structure formation with axion-like particle dark matter can have distinctive signatures on scales ranging from kiloparsecs to astronomical units. They are governed almost entirely by the particle mass and therefore very predictive. However, much of the phenomenology is highly nonlinear, requiring large simulations and, in some cases, novel computational tools. Very similar phenomena might have appeared in an early matter dominated epoch after inflation. Here, the inflaton field itself fragments gravitationally, forming structures on microscopic scales that closely resemble cosmological large-scale structure.

Cool cores occur in half of all clusters of galaxies, centred on the most massive galaxies known. The temperature of the intracluster gas drops inward as does the radiative cooling time, to well below a Gyr. Radio jets from the central AGN blow bubbles which can heat the gas and may prevent strong cooling.  There is however much cold gas near the centre of most cool cores which can hide the presence of cooling in soft X-rays. Here I show that significant hidden cooling flows may be occurring in a small sample consisting of the Centaurus, Perseus and A1835 clusters. This has consequences for the total mass and life cycle of the cold gas as well as for the rest of these highly multiphase regions.

We experience a golden era in testing and exploring relativistic gravity. Whether it is results from gravitational wave detectors, satellite or lab experiments, radio astronomy plays an important complementary role. Here one can mention the cosmic microwave background, black hole imaging and, obviously, binary pulsars. This talk will provide an overview how these methods relate to each other, and will in particular focus on new results from the study of binary pulsars, where we can test the behaviour of strongly self-gravitating bodies with unrivalled precision. The talk will also give a brief update on nHz gravitational wave detection with Pulsar Timing Arrays and an outlook of what we can expect from new experiments, such as MeerKAT or the SKA.

The CHaracterising ExOPlanet Satellite (CHEOPS) was selected in 2012 as the first small mission (S-mission) in the ESA Science Programme and successfully launched within schedule and budget on December 18, 2020 on a Soyouz-Fregat rocket from Kourou, French Guyana. CHEOPS is the first mission dedicated to search for exoplanet transits by means of ultrahigh precision photometry on bright stars already known to host planets. The follow-up of planets with a higher precision photometry improves the measurements of the planet properties such as radii, masses (via TTVs), even shapes, and allows for defining precise transit ephemeris especially for small bodies. It also often leads to a refinement of the overall architecture of the systems (e.g. discovery of new planets). By the same token, the measuring of occultations and phase curves with a precision of only a few parts-per-million has opened a new window on the study of the atmospheres of hot planets. Being agile and able to look at a large fraction of the sky, CHEOPS offers a unique interface between the discovery (e.g. TESS) of exoplanets and their further spectroscopic characterisation by large space- (e.g. JWST & ARIEL) or ground-based (e.g. VLT & ELTs) facilities.

Hydrodynamical cosmological simulations are increasing their level of realism by considering more physical processes, having more resolution or larger statistics. However, one usually has to either sacrifice the statistical power of such simulations or the resolution reach within galaxies. I will introduce the NewHorizon project where a zoom-in region of ∼(16 Mpc)^3, larger than a standard zoom-in region around a single halo, embedded in a larger box is simulated at high resolution. A resolution of up to 34 pc, typical of individual zoom-in state-of-the-art resimulated halos is reached within galaxies, allowing the simulation to capture the multi-phase nature of the interstellar medium and the clumpy nature of the star formation process in galaxies. I will present and discuss several key fundamental properties of galaxies and of their black holes. Due to its exquisite spatial resolution, NewHorizon captures the inefficient process of star formation in galaxies, which evolve over time from being more turbulent, gas-rich and star-bursting at high redshift. These high redshift galaxies are also more compact, and are more elliptical, disturbed and clumpier until the level of internal gas turbulence decays enough to allow for the formation of stable rotating discs. I will show the origin and persistence of the thin and thick disc components, and explain why the settling of discs "magically" occurs at around a stellar mass of 10^10 Msun.

The results of LIGO and Virgo open a new landscape for the study of binary black holes: we now know of nearly one hundred candidate systems. Because of the new data, theoretical and numerical models of binary black hole formation face a serious challenge: several LIGO-Virgo black holes have mass in the upper mass gap (~60-120 Msun) predicted by pair-instability theory, others partially overlap with the lower mass gap (~2-5 Msun). On the one hand, population models of massive binary stars predict black hole masses in the range ~ 3 - 50 Msun, with nearly aligned spins, but are affected by large uncertainties. On the other hand, dynamics of dense stellar clusters can trigger the formation of binary black holes with largely misaligned spins, and even fill the pair instability mass gap. In this talk, I will present new theoretical models of the formation of massive (>60 Msun) black holes via multiple stellar collisions and hierarchical mergers of low-mass black holes in dense star clusters. Furthermore, the redshift evolution of binary black holes is one of the key features to understand their formation, in preparation for next-generation gravitational-wave detectors.

Supernovae ultimately deposit ~10% of their total energy in a population of relativistic cosmic rays that subsequently interact with the interstellar medium (ISM) via magnetic forces. Because these particles lose energy to radiation only slowly compared to the ~90% of the supernova energy that is deposited in the ISM as heat, they are a potentially important feedback mechanism in galaxies despite their comparatively small energy budget. Their effectiveness, however, depends crucially on the poorly-understood plasma processes that couple them to the bulk, neutral ISM. In this talk I introduce a new, physically-motivated model for the coupling between cosmic rays and the neutral, star-forming ISM, and show that it successfully predicts the gamma-ray spectra of resolved nearby galaxies, the galactic IR-gamma correlation, and the cosmological gamma-ray background. I conclude by exploring the implications of
this model for the importance of cosmic ray feedback, demonstrating that this mechanism is likely unimportant for rapidly star-forming galaxies either today or in the early universe, but may be critical for local dwarfs and quiescent spirals.

Massive stars play important roles in many astrophysical systems by providing the radiative and mechanical energy output. They can also produce black holes and neutron stars when they explode. However, the traditional 1D stellar evolution models provide very uncertain predictions for the structure and evolution of massive stars because radiation acceleration around the envelopes of massive stars at the iron opacity regions can be much larger than the gravitational acceleration. I will show how we can understand convection in massive star envelopes and observational properties of massive stars in different locations of the HR diagram based on a series of first principle global 3D radiation hydrodynamic simulations. These simulations can be used to understand the physical origin of super-Eddington outflows from massive stars and the outburst behavior of luminous blue variables. I will demonstrate these simulations can directly produce the low frequency variabilities of many O stars as observed by TESS recently. I will also show simulations of Red Supergiants, which are used to predict observational properties of supernova shock breakouts. Finally, I will illustrate how these simulation results can be used to improve the traditional 1D stellar evolution calculations, which can provide much more reliable models of massive stars.

These are incredibly exciting times for extra-galactic astrophysics; above all for studies of galaxy formation and growth of structure. New observatories and advanced simulations are revolutionising our understanding of the cycling of matter into, through, and out of galaxies. In this talk I will provide an overview of the normal matter in collapsed structures, their chemical make-up and dust content. I will present fresh clues of the cosmic evolution of cold gas; revisit the 20-year old "missing metals problem" and introduce new calculations of the dust content of the Universe up to early times. Together, these results provide an increasingly accurate description of the baryon cycle which plays many crucial roles in transforming the bare pristine Universe left after the Big Bang into the rich and diverse Universe in which we live today.

If Earth lost its magnetic field, would its ability to support life be diminished? If Mars had retained a strong magnetic field, would it be habitable today? For decades it was assumed that the answers to these two questions were “yes”. In recent years, however, the canonical assumption that planetary magnetic fields improve planetary habitability has been called into question. This presentation will review the perceived connections between magnetic fields and surface and atmospheric habitability of planets and discuss several approaches to resolving this important question: (1) intercomparison of observations of Venus, Earth, and Mars, (2) analysis of observations from unmagnetized and magnetized regions of Mars, and (3) development of large computer simulations for the interaction of a star with a planet’s atmosphere and magnetic field. In the end, all approaches are likely to be necessary. We will discuss an ongoing team science effort named MACH that draws on expertise from the heliophysics, planetary, and exoplanetary communities.

Black holes are ubiquitous throughout the universe, being born at the earliest times, lurking at the centres of galaxies, roaming undetected through local space, and at the heart of the most extreme astrophysical transients: GRBs, TDEs and gravitational wave bursts. It is the interaction between two coupled phenomena in the direct environment of the black hole, accretion and outflow, which largely determine how we observe these bizarre objects. Relativistic outflows or jets are usually detected via the synchrotron signature associated with relativistic electrons, and the radio band is the best place to see this signature. In this talk I will highlight new advances in the understanding of jets, their power and their propagation through the ambient medium. This will be discussed in the context of jets from stellar mass black holes in binary systems, but has a broader context applicable to all black holes. In particular I will focus on what three years of observations with MeerKAT, as part of the ThunderKAT project, have revealed to us about the large-scale propagation and deceleration of powerful jets from the very moment of launch to their terminal deceleration in the interstellar medium approximately one year later.

Education and its contribution to science, technology, and innovation are the key points for combating poverty in the long term. Education is also a key point for empowering girls and women, which is fundamental for achieving the United Nations Sustainable Development Goals (SDGs). Astronomy is a powerful tool to promote education and science but, in addition to that, it is also one of the leading sciences for bringing strong technological developments and innovation. Africa has amazing potential due to natural and human resources for scientific research in astronomy. The status of astronomy and space science in Africa changed significantly over the past years, becoming emerging fields across the continent, and never before it was more possible to use astronomy for development as it is nowadays.

This talk will summarise different activities carried out for education, science, and technological development in Ethiopia, East Africa, and across the continent, and show how through them we can fight poverty in the long term, and increase in future our possibilities of attaining the United Nations Sustainable Development Goals (SDGs) for the benefit of our all society.