Events, Seminars, Talks

Abstract
The search for the origins of cosmic rays has been a thorn in the side of high-energy astrophysicists for more than a century. This talk will provide an overview of the current state of understanding regarding the origins of cosmic rays, highlighting some of the outstanding problems and challenges. I will provide some examples of how recent gamma-ray observations are advancing the field, and how the next generation of gamma-ray observatories may crack this long-standing problem Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09

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Mass loss plays a crucial role in the lives of massive stars, especially as the star leaves the main sequence and evolves all the way to the red supergiant (RSG) phase. Despite its importance, the physical processes that trigger mass loss events in RSGs are still not well understood. In this talk, I will introduce our new method to reproduce the atmospheric extensions of these cool evolved stars, where mass-loss events take place. I will also discuss the accuracy of our models when comparing the spectral energy distributions (SEDs) and interferometric visibilities with newly obtained VLTI/GRAVITY and MATISSE observations. This new methodology represents a step forward in modelling the winds of cool evolved stars.

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All planetary atmospheres are 3D in nature. This is particularly true for the majority of exoplanets we observe today : tidally-locked, close in, giant planets. Atmospheric flow from the dayside to nightside of these worlds shape the 3D thermal, chemical and cloud structure. Understanding this 3D structure is crucial to properly interpret current and future observations.

I will show how recent breakthrough in telescopes and instrumentations allow us directly measure dynamical quantities and map the 3D structure of exoplanets. I will particularly highlight how wind speeds can be directly measured from ground-based high-spectral resolution observations and how temperature, chemical and cloud maps can be obtained through JWST observations, including the recently observed NIRspec/PRISM phase curve of the hot Jupiter NGTS-10b.

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WEAVE is the next-generation wide-field survey facility for the William Herschel Telescope (WHT). WEAVE will provide the instrument required for full scientific exploitation of the Gaia, LOFAR, and APERTIF surveys in the Northern Hemisphere. WEAVE is a multi-object and multi-integral-field-unit (IFU) facility utilizing a large, new 2-degree-diameter prime focus corrector at the WHT with a pick-and-place fibre positioner system hosting nearly 1000 multi-object fibres or 20 mini-IFUs for each observation, or a single wide-field IFU. The fibres are fed into a dual-beam spectrograph located in the GHRIL enclosure on the WHT's Nasmyth platform. The spectrograph records nearly 1000 spectra simultaneously at a resolution of R~5000 over an instantaneous wavelength range of 360-950 nm or at a resolution of R~20000 over two more-limited wavelength ranges. WEAVE has been on sky since late 2022. The WEAVE Survey will provide complete phase-space coordinates of roughly 3 million stars in the northern sky selected with ESO’s Gaia satellite, chemical analysis of more than 1 million stars from Gaia, half a million massive stars in the Galactic Plane, distances and properties of galaxies selected from the low-frequency radio-wave surveys being conducted with LOFAR, “three-dimensional" spectroscopy of galaxies selected from surveys using the new Apertif focal plane array at WSRT, and deep surveys of galaxy clusters and moderate-redshift galaxies. In this talk I will discuss the motivation, design, construction, and commissioning of WEAVE and the “first-light”, Science Verification, and early WEAVE Survey data we’ve already collected with it. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Professor Trager is available for meetings by arrangement with his hosts, Kathryn Kreckel (kathryn.kreckel@uni-heidelberg.de) and Cormac Larkin (cormac.larkin@uni-heidelberg.de).

Abstract
Intense star formation and rapid black hole accretion in the centers of galaxies produce energy that propels gas outward. These galactic winds affect the evolution of their host galaxies, self-regulate the future growth of stars and black holes, and populate the enormous reservoirs of gas surrounding them. In the past decade, optical and near-IR integral field spectroscopy (IFS) from the ground has revolutionized the study of galaxy-scale outflows that reach into the their surroundings. The unprecedented infrared sensitivity, spatial resolution, and spectral coverage of the JWST IFUs is also transformative for studying these outflows at new, mid-infrared wavelengths. I will discuss observations of galactic winds driven by star formation and black holes at redshifts z ~ 0.5 that probe their extent and properties and illuminate the connection between galaxies and their surroundings.

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Abstract to be announced. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Dr Decarli is available for meetings by arrangement with his host, Kathryn Kreckel (kathryn.kreckel@uni-heidelberg.de)

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As an interim between Gaia DR3 (2022) and DR4 (2026), ESA and the science consortium have published five new data sets derived from Gaia observations, including four entirely new data types, and one drastically improved data set. Contrary to the main releases, which address almost any area of astronomy, these data sets are more specialized. In the talk I will briefly describe them: Drastically improved minor-planet orbits, newly discovered gravitational lenses (multiple images of quasars), half a million additional Gaia stars in the core of omega Centauri, the three-dimensional distribution of diffuse interstellar bands in stellar spectra, the radial-velocity variations of long-period pulsating variables. Gaia DR4 will present a large number of new data types, and strong improvements in many of the already established ones. The present data sets are partly meant to enable follow-on work prior to DR4, and partly as "appetizers" for things to come in 2026.

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Recent observational successes are providing a new impetus to the study of binaries containing stellar-mass black holes. I will start with a very brief review of the current understanding of massive binary evolution leading to the formation of black-hole binaries. I will then focus on a few of the outstanding issues in interpreting both X-ray and gravitational-wave observations and propose pathways for improving our understanding of some challenging aspects of binary evolution. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During his visit to Heidelberg, Professor Mandel will be available for meetings by arrangement with his hosts, Friedrich Roepke (roepke@uni-heidelberg.de) and Fabian Schneider (fabian.schneider@h-its.org)

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If you are looking for astronomical data – catalogues, images, spectra, time series, whatever –, consulting the Virtual Observatory Registry is an excellent idea. Using an interface the Heidelberg GAVO group have recently contributed to astropy-affiliated pyVO package, you now can do so from the comfort of your jupyter notebook. In this talk, I will show you how to build queries and how to use their results. This will also serve as a very hands-on introduction into the Registry’s data model and its remaining limitations, in particular as regards “blind discovery”: data collection discovery based on physical characteristics of what a researcher is looking for rather than on project or instrument names.

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Cosmological and astrophysical data are now sufficiently large and complex to become almost intractable by traditional statistical techniques. Unravelling the twin mysteries of dark energy and dark matter will require new data analysis methods capable of extracting knowledge from upcoming data streams, including the Euclid satellite, the Nancy Grace Roman space telescope, LSST/Vera Rubin observatory and LISA. While machine learning offers great promise, it suffers from difficulties in interpretability as well as from poor generalisation when the training set is not representative of the target data (known as “covariate shift”) - an almost ubiquitous problem in astronomy due to selection effects.  I will motivate and present some of the latest machine learning tools being developed for fast and scalable inference, focusing on simulation based inference and particularly on neural ratio estimation for amortised marginal posterior inference as the natural heir to classical Bayesian inference techniques. I will then discuss a general, statistically principled solution to covariate shift in supervised learning, which achieves gold standard performance in a variety of important test cases. I will conclude with example applications in supernova type Ia cosmology, dark matter direct detection and gravitational waves astronomy. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During his visit to Heidelberg Professor Trotta will be available for meetings by arrangement with his host, Ivelina Momcheva (momcheva@mpia.de).

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Many areas of astrophysics rely on accurate results from stellar evolution models, in particular those of massive stars due to their importance as sources of ionizing flux and chemically enriched material. One of the biggest drivers in the evolution of massive stars is their mass loss rate, but alas this is also still one of their least well-constrained properties. In this talk, I will explore the impact of mass loss in stellar evolution models more deeply, comparing the effect of applying different mass loss rates during the main sequence of massive stars. Strikingly, the results show that the main sequence mass loss is able to affect the interior structure of a massive star down to its core, which has complex repercussions for its subsequent evolution and final fate. At the end of the talk, I will discuss the impact of these results for the applicability of stellar evolution models and address the problems and uncertainties that remain to be investigated.

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At the core of galaxy evolution is the evolution of the baryonic components that modify the observable properties of galaxies. A crucial component of baryonic matter is the interstellar medium (ISM) that consists of gas and solid-phase metals called dust. Interstellar dust determines how galaxies look like from UV to sub-mm, how the ISM behaves, and the very process of star formation that creates the stellar component that defines a galaxy. We are now at the beginning of an exciting journey with the unprecedented infrared capabilities, high sensitivity, and high angular resolution of JWST/MIRI compared to its predecessors such as Spitzer. For the first time, we are able to not only detect warm dust emission in individual typical galaxies across masses and star formation rates (SFRs) at cosmic noon, but also resolve the dust-obscured SFR in more extended sources at z~1. In this talk, I will show the recent results of my research on a panchromatic study of dust emission and absorption properties of galaxies at cosmic noon and review the new results from our multi-band MIRI survey, SMILES, covering 5 to 25um wavelength in HUDF. This extensive survey focuses on obscured AGN and star formation within cosmic noon galaxies, extending our reach to galaxies with stellar masses an order of magnitude lower than ever observed before. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During her visit to Heidelberg Dr Shivaei will be available for meetings by arrangement with her host, Leindert Boogaard (boogaard@mpia.de)

Abstract
Albeit rare in absolute numbers, massive stars are shaping our cosmic history as they are connected to many astrophysical key processes. Commonly defined as stars with an initial mass of more than 8 times the mass of our Sun, massive stars are the progenitors of black holes and neutron stars, reaching all nuclear burning stages before eventually undergoing their inevitable core collapse. In their relative short, but wild life, these luminous objects have an enormous impact on their galactic environment, enriching the surrounding medium with momentum, matter and ionizing radiation. This so-called "feedback" of massive stars is a building block for the evolution of galaxies, initiating and inhibiting further star formation. In the "afterlives" of massive stars, black holes and neutron stars can merge with each other, giving rise a to Gravitational Wave events. Many details of massive stars as well as their impact and evolution are still poorly understood. In fact, the overall picture we draw in textbooks often does not hold once we actually try to bring all the observational and theoretical constraints together. We nowadays know that many massive stars have one or more companion and interactions between massive stars are common. While this gives rise to different evolutionary channels, many challenges remain. Further unconventional puzzle pieces and surprising constraints have arrived from observational frontiers such as the strong metal-enrichment in high-redshift galaxies discovered by JWST or the black hole statistics obtained from Gravitational Waves. Investigating the massive star puzzle with a combined approach of theory, observation and numerics is at the very heart of my research group at the ARI. Our central tool in this endeavour is the application and development of dedicated stellar atmosphere models. I will briefly introduce the techniques and challenges of atmosphere modelling for hot, massive stars and their winds as well as their empirical and theoretical applications. Afterwards, I will provide an overview about the multi-ranged research efforts in my group, ranging from the spectral analysis of individual stars and the identification of "hidden" companions over theoretical studies on radiation-driven winds up to the generation of synthetic stellar libraries and new predictions for stellar feedback.

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Abstract to be announced. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During her visit to Heidelberg, Professor Zasowski will be available for meetings by arrangement with her host, Dominika Wylezalek (wylezalek@uni-heidelberg.de)

Abstract
Supernova feedback injects energy and turbulence, influencing the star formation process, and is therefore essential to understanding the formation and evolution of galaxies. Supernova remnants exhibit distinctive emission line ratios and kinematic signatures, which are apparent in optical spectroscopy. Using optical integral field unit data from PHANGS-MUSE collaboration project, we are able to identify supernova remnants within 19 nearby galaxies. We use a combination of five different optical diagnostics to identify SNRs. We account for the influence of diffuse ionized gas, using the line ratio maps of [SII]/Halpha and [OI]/Halpha in comparison with the Halpha surface brightness to select out supernova remnants. In addition, the velocity dispersion map and line ratio diagnostic diagrams are also useful ancillaries to confirm their identification. We identify 2399 supernova remnants within 19 nearby galaxies. This paper catalogs optical SNRs from PHANGS-MUSE and characterizes them. ~ 33% of SNRs lie within HII regions. In the five criteria we use to identify SNRs, in comparison with the Halpha surface brightness works best that select out 1482 SNRs. We also define a clean sample of 1276 SNRs that have been detected in at least two diagnostics, giving us high confidence in our characterization of these as SNRs. Overall, our detection of ~ 130 SNRs per galaxy implies an SN rate of 1~2 per century in our sample.

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Abstract to be announced. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During his visit to Heidelberg, Professor van de Ven will be available for meetings by arrangement with his host, Nadine Neumayer (neumayer@mpia.de)

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The study of voids and galaxies residing there is crucial for our understanding of the formation and evolution of galaxies. Galaxies in voids in general reveal lower metallicity at a given luminosity than similar objects in the denser environment. Several mechanisms can be responsible for this effect, such as metal-poor gas accretion, mergers/interactions, or the unevolved state of a galaxy. In my talk, I will present our observations of void galaxies and focus on different mechanisms affecting their properties and evolution. We found a population of extremely metal-poor dwarfs that are supposed to be good candidates for very young galaxies in the nearby Universe. The non-equilibrium state of their gaseous HI discs supports the hypothesis of their suggested unevolved state. Besides, we found strong misalignments between gas kinematics and optical morphology together with peculiarities in their chemical abundances for several more massive void galaxies that can be explained by dwarf-dwarf mergers or recent episodes of gas accretion. In particular, our new results on VGS ? 12 - a galaxy with HI polar disc, sitting in the wall between two voids, reveal strong evidence of metal-poor gas accretion from the Cosmic Web.

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