Main Colloquium
Dr. Markus Boettcher	ORATED

North-West University, Potchefstroom, South Africa

Blazars are the most numerous extragalactic sources of high-energy and very-high-energy gamma-rays and are bright and variable throughout the entire electromagnetic spectrum. Their non-thermal continuum emission is dominated by radiation from a highly relativistic jet moving closely aligned to our line of sight. Many open questions concerning the physics of particle acceleration and production of the multi-wavelength emission remain. Polarization is a key indicator of the structure of magnetic fields in these sources and the role they play in the acceleration and radiation processes. While traditionally, measurements of polarization were possibly only at radio and optical wavelengths, the recent successful launch of the Imaging X-Ray Polarimetry Explorer (IXPE) has opened a new window of X-ray polarimetry. This talk will introduce the principles of the processes to produce and measure polarized multi-wavelength emission and recent results, in particular from IXPE and co-ordinated multi-wavelength observations.

	Special Colloquium
Felix Pötzl	ORATED

MPIfR

The nature of dark matter (DM) remains elusive. Currently viable DM models, such as the standard cold dark matter (CDM) model and alternative models developed to address its shortcomings - including warm DM, fuzzy DM, and self-interacting DM - differ in their predictions for DM halos at critical, sub-galactic scales. If sufficiently dense, these sub-galactic DM halos could form a population of supermassive compact objects (SMCOs). SMCOs could potentially also consist of a population of free-floating (primordial) supermassive black holes (SMBHs), that are DM candidates. These DM halos are nearly devoid of stars, and so any SMCO may possibly be detected only through the gravitational effect they exert on ordinary matter. The SMILE (Search for MIlli LEnses) project aims at probing the number density of low mass (~10^6-10^9 solar masses) DM halos via a search for gravitational lens systems at milliarcsecond scales (milli-lenses), where the lens is expected to have a mass in the range of interest. This is achieved by studying radio images of active galactic nuclei made with very-long-baseline interferometry (VLBI). In a recent pilot project, we conducted a search for milli-lens candidates in a sample consisting of 13,828 compact radio sources from the Astrogeo VLBI FITS image database. Forty candidates with compact double structures have been found using a citizen-science approach, for which I will present the final analysis of follow-up observations with the European VLBI Network at 5 and 22 GHz in phase-referencing mode. These observations with increased sensitivity and frequency coverage allow us to better constrain the nature of the lens candidates. I will highlight our observational strategy, with which we can confidently reject most systems as milli-lenses, given constrains such as surface brightness ratio, stability of flux density ratio of components over time, and their spectrum. Rejected candidates are still interesting as potential compact symmetric object (CSO) or even supermassive black hole binary (SMBHB) candidates. I will put the pilot study in the context of the SMILE project, which ultimately aims at using a sample of ~5,000 sources based on the Very Large Array (VLA) Cosmic Lens All-Sky Survey (CLASS), and largely has redshifts available. This enables us to test our future findings against theoretical predictions from different DM models.

	Main Colloquium
Andreas Quirrenbach	ORATED

The tools of spectral analysis first developed by Kirchhoff and Bunsen in the 19th century enable us to determine the composition and physical properties of celestial bodies. Recent refinements of these techniques have yielded first glimpses into the structure and chemistry of the atmospheres of giant gas planets orbiting stars in the Solar neighborhood. At the same time, technologies are being developed that will extend the reach of spectroscopic measurements to smaller rocky planets, with the goal of probing their suitability for harboring life. I will describe the design of optical systems capable of detecting planets that are 10^10 times fainter than their host stars, and discuss their use in the exploration of habitable worlds.

	Promotionskolloquium
Aleksei Nikonov	ORATED

MPIfR

Relativistic jets from Active Galactic Nuclei (AGN) are powerful plasma streams that play a pivotal role in galaxy evolution and act as natural particle accelerators. The jet in M87, driven by a supermassive black hole, is an ideal target for studying jet dynamics due to its proximity and the exceptional mass of its central black hole. This research investigates the inner 100 parsecs of the jet with sub-milliarcsecond resolution using very long baseline interferometry (VLBI), uncovering a helical structure attributed to Kelvin-Helmholtz instabilities, observed for the first time on parsec scales. The study also focuses on HST-1, a prominent knot in the jet located in the transition region where the flow evolves from parabolic to conical collimation and shifts from magnetically to kinetically dominated dynamics. The unique position of HST-1, coupled with its potential gamma-ray flaring activity, has led to its interpretation as a recollimation shock. However, the discovery of Kelvin-Helmholtz instabilities both upstream and downstream of HST-1 suggests that the knot’s origin may not be shock-related. High-resolution VLBI observations provide spectral index and turnover frequency maps, offering critical insights into HST-1's structure and magnetic field strength.

	Main Colloquium
Dr. Giulia Illuminati	ORATED

INFN-Bologna

KM3NeT is the next-generation neutrino observatory currently under construction in the Mediterranean Sea, already taking data in a partial configuration. By covering a vast energy range with its ARCA and ORCA detectors, KM3NeT can investigate a variety of scientific topics, including neutrino astronomy, oscillation studies, and dark matter searches. I will present the recent results in all these fields and discuss the exciting prospects KM3NeT offers for advancing our understanding of the cosmos and the fundamental properties of neutrinos.

	Master Colloquium
Parisa Rahimi	ORATED

MPIfR

The BRAND receiver is a new system mainly intended for the EVN that covers the remarkably broad contiguous frequency range of 1.5 GHz to 15.5 GHz. It includes all required components of the entire signal path from the cryogenic frontend, feed, amplifiers, hybrids, a 56 Gsps sampler down to the VLBI backend and is intended for VLBI and single-dish work. This band coverage offers flexibility for redshifted spectral lines, sensitivity and frequency agility in the EVN. In my thesis I present the integration tests recently carried out an initial commissioning of the BRAND components into a prototype system installed in the Effelsberg 100 m telescope. This continues the development from the RadioNet BRAND-EVN project. This work is based on technical tests on the cryogenic-, IF-, and data-acquisition system in Bonn and Effelsberg. On-sky tests include single-dish spectroscopy and VLBI resulting a 1.5 to 12 GHz bandwidth spectrum of W3 cloud and VLBI fringes on all baselines. The first on-sky measurements with the latest and broadest-band member in the family of broad-band receivers (C/X with fractional bandwidth of 80 %, UBB with 130 % and BRAND with 165 %) have been done. Cross scans and Moon observations have resulted in a $T_"sys"$ of around 90 K. From the spectrum of the W3, 57 radio recombination lines were detected, and from a VLBI session between four EVN stations, fringes were detected. This has allowed an assessment on the real-world performance in various scenarios, e.g. astronomical as well as geodetic VLBI and single-dish applications and should help inform the decision-making about future EVN capabilities.

	Main Colloquium
Dr. Yannis Liodakis	ORATED

MPIfR

Supermassive black holes form the most intriguing astrophysical systems offering countless opportunities to study fundamental physics in regimes not accessible to laboratories on Earth. Their multimessenger emission manifests in the formation of accretion disks, jets, and the acceleration of extremely energetic particles all of which are still poorly understood. Polarization can provide answers to long standing black hole physics questions. However, the necessary instruments for such a task were, until recently, missing. I will discuss recent efforts to understand blazars and tidal disruption events through their polarized emission across the electromagnetic spectrum.

	Master Colloquium
Camilla di Giusto	ORATED

MPIfR

Sulphur-bearing species could be used as evolutionary tracers of high-mass star formation. In this context, we studied the molecular emission and absorption of S-bearing species towards Galactic high-mass star-forming clumps. We analyzed spectroscopic observations obtained with the APEX telescope and the SOFIA mission towards 131 clumps of the ATLASGAL survey at 870 μm. Among those, the ATLASGAL "Top100" sample contains the brightest sources in all evolutionary stages of the high-mass star formation process. We detected rotational line transitions of ortho-H2S, para-H2S, OCS, SO and H2CS. While most of the spectra showed single Gaussian emission, signatures of outflows, self-absorption and infalling/expanding envelopes were also found. Assuming LTE conditions, the column densities and abundances of each species were derived. The species abundances showed a loose correlation with the luminosity and evolutionary stage of the clumps. In addition, the ortho-to-para ratio (OPR) of H2S was determined using H2S low frequency lines but found to be degenerate with temperature. By assuming a thermalized OPR value of 3, temperatures of the order of 100 K were found for the H2S emission, pointing to a hot core origin. The spherical non-LTE radiative transfer model RATRAN was used to study the H2S line profiles. However, the model did not reproduce well the observed spectra suggesting a more complex source morphology.

	Main Colloquium
Dr. Sebastian Bocquet	ORATED

LMU

With the latest generation of cosmological datasets, we are accessing an unprecedented wealth of information on the geometry and expansion of the universe and on the growth of cosmic structure. This has allowed for tight constraints on, e.g., the properties of neutrinos and dark energy, but also uncovered anomalies such as the Hubble tension and the S8 tension. The abundance of galaxy clusters, the clustering of galaxies, and weak gravitational lensing are key probes of the cosmic large-scale structure. Over the past decade, tremendous progress was made in obtaining high-precision measurements, notably thanks to sensitive wide-field surveys of the cosmic microwave background (CMB) and of galaxies and gravitational lensing. Recently, the abundance of clusters selected in CMB data from the South Pole Telescope (SPT) — in combination with mass calibration based on weak-lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST) — was shown to be compatible with and complementary to analyses of galaxy clustering and weak lensing (3x2pt using, e.g., DES data). In my talk, I will review the SPT cluster cosmology and mass calibration program. I will focus on the latest SPT + DES + HST analysis and discuss the resulting cosmological constraints. I will then present new results from the multiprobe analysis of SPT clusters and DES 3x2pt. The precision of these new constraints highlights the benefits of multiwavelength multiprobe cosmology and our work paves the way for upcoming joint analyses of next-generation datasets.

	Special Colloquium
Prof. Matteo Viel	ORATED

Trieste Observatory (INAF-OATS)

I will review the use of the Intergalactic Medium, the cosmic web connecting galaxies, as a high redshift probe to constrain fundamental physics (dark matter, neutrinos) and baryonic physics (thermal state of the gas and reionization). On the data side, I will show how Lyman-alpha forest quasar spectra are providing such unique small scale information. On the theory side, I will rely on hydrodynamic simulations which incorporate the relevant physics.

	Special Colloquium
Prof. Dipanjan Mitra	ORATED

Tata Institute of Fundamental Research

More than fifty years have passed since the discovery of pulsars, yet the physical mechanism of their coherent radio emission remains unclear. In normal pulsars (periods > 0.05 sec), the linear polarization position angle (PPA) tracks across the pulse follow a S-shaped curve that can be explained by the rotating vector model (RVM), which forms the basis for our understanding of emission physics. In several pulsars one RVM-like PPA track can be seen, while in other cases two parallel orthogonal RVM-like PPA tracks are visible. However, in an equally large sample of pulsars the PPA traverses have complex, non-RVM patterns, that makes it difficult to identify a unique emission mechanism for the pulsar population. As a result, the fundamental question of whether the outgoing waves from pulsar magnetospheric plasma is excited by a maser or antenna mechanism or from any other physical process, has remained unresolved. In this talk I will present high quality single pulse polarization observations that we believe have potential to finally resolve the problem of identifying the emission mechanism. I will show examples of single pulse emission with high levels of linearly polarized signals that follow RVM, especially in pulsars with complex PPA patterns. These results strongly favour the coherent curvature radiation (antenna like) mechanism to be universally applicable in the normal pulsar population. The single or two orthogonal RVM-like PPA tracks can be associated with the propagating eigen-modes of strongly magnetized pair plasma.

	Special Colloquium
Erandi Chavez	ORATED

Center for Astrophysics

Does the supermassive black hole at the center of our galaxy, Sagittarius A* (Sgr A*), have a jet? Results from Event Horizon Telescope (EHT) data favor accretion flow models in which one is present, however, it has not been conclusively detected. Using simulated data based on the 2017 EHT best-best models of Sgr A*, we explore the possibility of detecting this jet with existing and next-generation VLBI arrays at 86, 115, 230, and 345 GHz. The competing astrophysical effects of jet power, jet variability, and interstellar scattering due to ionized plasma between Earth and the Galactic Center add complexity to the prospects for jet recovery in images of Sgr A*. In addition, the VLBI arrays we consider have different array configurations and instrument sensitivities that significantly influence their ability to image the jet. While current VLBI arrays are unable to capture the jet, next-generation arrays at 86 and 115 GHz such as the ngVLA and the next-generation EHT are able to image the jet. The prospects towards detecting a jet in Sgr A* are bright and motivate the continued development of these next-generation radio observatories.

	Main Colloquium
Dr. Timothy Davis	ORATED

Cardiff University

In this talk I will describe how mapping the dynamics of gas clouds in the centre of galaxies can help us to constrain a wide range of astrophysical problems. From the enigmatic relation between galaxies and their supermassive black holes, to the suppression of star-formation in dying galaxies, the dynamics of cold gas provides an ideal probe that can help us make progress. I will show how parsec resolution ALMA observations can be used to estimate the masses of supermassive black holes in galaxies across the Hubble sequence, both dynamically, and via the newly discovered ‘fundamental plane of black hole accretion in the millimetre”. I will describe the WISDOM and WONDER projects, that aims to use this technique to constrain the importance of accreting SMBHs in galaxy quenching. I will go on to show that, contrary to expectations, molecular gas appears to be an important source of fuel for accretion in even low-luminosity, low-excitation active SMBHs. Finally, I will show that the deep potential wells of massive galaxies change the small-scale structure of the ISM, suppressing star formation, and helping to keep bulge-dominated objects quenched.

	Special Colloquium
Prof. Jeroen Stil	ORATED

University of Calgary, Canada

Faraday rotation of linearly polarized radio waves in a magnetized plasma has been, for decades, the foremost important observational probe of cosmic magnetic fields from kiloparsec to megaparsec scales. The Rotation Measure Grid, a list of (mostly) extragalactic sources with measured Faraday rotation, is the starting point for much of the science from large polarization surveys with radio interferometers, including the Square Kilometre Array. With the attainable bandwidth of order 1 GHz in L-band, measurement errors of Rotation Measure (RM) are of the order of 1 rad/m2, much smaller than the scatter imposed by many astrophysical plasmas. Faraday rotation of a turbulent plasma with structures on a range of scales that are smaller than the beam, imposes not only depolarization, but also scatter in Rotation Measure, referred to as RM jitter. This RM jitter is a form of scatter in the RM grid that depends on the amplitude and slope of the power spectrum of structure in the plasma, but also on the observed wavelength range. Models of this kind can reproduce higher RM scatter for sources that are less polarized, as recently observed in the POSSUM survey by Vanderwoude et al. (2024). They also provide a new framework for the interpretation of polarimetry of radio sources over bandwidths of a few GHz, for example when combining data from the THOR and GLOSTAR surveys. New? Such models were already examined by Tribble (1991)!

	Special Colloquium
Dr. Jacob Roth	ORATED

MPA

Radio astronomy aims to image the radio sky with ever-higher resolution and sensitivity. To this end, larger telescopes are built, and novel algorithms for processing the data are developed. This talk focuses on imaging algorithms for producing high-dynamic-range, high-resolution maps of the radio sky. More specifically, I will present the fast-resolve algorithm. fast-resolve is a Bayesian radio interferometric imaging algorithm building on the resolve framework. fast-resolve uses a major-minor cycle scheme, significantly reducing the computational cost of previous Bayesian imaging algorithms. These developments enable, for the first time, a Bayesian reconstruction of a large MeerKAT dataset.

	Main Colloquium
Prof. Dr. Leon Koopmans	ORATED

Groningen University

Observations of the first luminous cosmic structures, with ground and space-based optical and infrared telescopes, are slowly lifting the veil on the complex physical processes that governed the Epoch of Reionization and Cosmic Dawn. These observations, most recently with JWST reaching redshift well into the Cosmic Dawn, however, are only the tip of the iceberg: islands in a sea of neutral hydrogen. I will review the current status of the LOFAR Epoch of Reionization Key-Science Program, presenting our latest improved power-spectrum limits on the 21-cm signal of neutral hydrogen, the constraints it sets on the high-redshift IGM, and present several breakthroughs in our understanding of the data itself, which will be crucial for the future SKA. I will also show the latest results from the NenuFAR Cosmic Dawn Key-Science Program, which aims to measure the 21-cm signal during the Cosmic Dawn. I will place these results in context of SKA and our plans to push towards 21-cm cosmology of the Dark Ages using space-based receivers, such as ALO, currently a pre-phase-A concept for a radio telescope to be placed on the lunar farside by ESA's Argonaut landers.

	Special Colloquium
Dr. Elena Shablovinskaya	ORATED

Instituto de Estudios Astrofísicos, Universidad Diego Portales, Chile

Mm emission has been observed as an excess in the SED of RQ AGN. Observations with ALMA have confirmed that mm emission originates from the central, very compact nuclear region (≤ 1 pc) and remains unresolved even at 0.1". While the origin of this emission is still debated, the observed mm spectra and the tight correlation between X-ray and mm emissions suggest that it is a self-absorbed synchrotron emission coming from the accretion disk X-ray corona. Although this mechanism is the most preferable, the absence of correlated variability between high-resolution ALMA mm observations (100 GHz) and X-ray bands (2–10 keV), as recently found in observations of IC 4329A, a nearby unobscured RQ AGN, raises the question about the origin of compact mm emission again. In this talk, I will present the latest results of the investigation of compact mm emission in RQ AGN, including the surprisingly high mm variability, which exceeds that in X-rays. I will also discuss the possible mechanisms for variability in the compact, corona-size region where the mm emission originates, as well as the very first attempts to define the mm origin using ALMA mm polarimetry.

	Special Colloquium
Ainara Saiz Perez	ORATED

University of Wuerzburg

The accretion of matter and the formation of relativistic jets in the vicinity of supermassive black holes are closely associated with the acceleration of particles to non-thermal distributions, but the mechanisms behind the coupling of relevant physical processes are not yet fully understood. M87*, the only source for which the black hole horizon scales and jet emission have been spatially resolved, may provide us with an insight into these physical mechanisms. We specifically aim to understand the role and importance of non-thermal particles in the structures observed by mm-VLBI techniques. For this purpose, we carried out general relativistic magnetohydrodynamic (GRMHD) simulations of a jet launching scenario, modelled after M87*. We followed up with radiative transfer calculations, accounting for the synchrotron emission of particles in a hybrid distribution, thermal in the accretion disk and non-thermal in the jet. The non-thermal particles are injected in regions subject to magnetic reconnection, following distributions modelled after particle-in-cell simulations. We find that non-thermal particles may play a crucial role in understanding the images of black hole environments on event horizon scales.

	Promotionskolloquium
Yaoting Yan	ORATED

MPIfR

My thesis investigates the influence of stellar objects onto the interstellar medium (ISM), following two lines of research, determining isotope ratios over much of the Milky Way and observing interstellar ammonia masers. Isotope abundance ratios provide a powerful tool to probe stellar nucleosynthesis, to evaluate the composition of stellar ejecta and to constrain the chemical evolution of the Milky Way. Molecular maser lines are signposts of star formation, probing the excitation and kinematics of very compact regions in the close environment of young stellar objects and providing useful targets for trigonometric parallax measurements. In the first part of this talk, I will present our observations of the J = 2-1 and 3-2 rotational transitions of various rare isotopologic variants of carbon monosulfide (CS), namely C33S, C34S, C36S, 13CS, 13C33S, and 13C34S, toward a large sample of 110 high-mass star-forming regions (HMSFRs) with the IRAM 30-meter telescope. With accurate distances obtained from trigonometric parallaxes, we confirm the previously identified 12C/13C and 32S/34S gradients as a function of Galactocentric distance. There is no 34S/33S gradient, but ratios are well below the values commonly reported in earlier publications. For the first time, we report positive gradients of 32S/33S, 34S/36S, 33S/36S and 32S/36S in our Galaxy. The Galactic 12C/13C gradients derived based on measurements of CN, C18O, and H2CO are in agreement with our results from C34S and indicate that chemical fractionation has little effect on 12C/13C ratios. The measured 34S/33S ratios as a function of Galactocentric radius indicate that 33S has a nucleosynthesis origin similar to that 34S. Interstellar 34S/33S values near the solar neighborhood suggest that the solar system ratio is, as perhaps also the 18O/17O ratio, peculiar. Our measurements support that 36S is a purely secondary nucleus; however, we note that data for lines containing this isotope are still sparse, particularly in the inner Galaxy. The predicted 12C/13C ratios from the latest Galactic chemical evolution (GCE) models are in good agreement with our results, while our 32S/34S and 32S/36S ratios show larger differences at larger Galactocentric distances. 32S/33S ratios show an offset across the entire inner 12 kpc of the Milky Way. All of this can serve as a guideline for further refinements of GCE models. The rest parts of this talk I will focus on ammonia (NH3) masers in our Galaxy. With the Effelsberg 100-m telescope, we discovered widespread non-metastable NH3 maser emission toward 17 high mass star forming regions (HMSFRs) in the Milky Way. This doubles the number of known non-metastable ammonia masers in our Galaxy. These maser lines arise from energy levels between 342 K up and 1449 K above the ground state and this probe the hot dense immediate neighborhoods of newly formed stars. With our higher angular resolution interferometric measurements from the Karl G. Jansky Very Large Array (JVLA), we determined detailed locations for maser spots emitted in multiple non-stable transitions toward a variety of regions. We greatly increase the number of detections in the Galaxy in all the lines targeted. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are >400 K and reach values up to several 10^5 K, manifesting the lines' maser nature. In view of the masers' velocity differences with respect to adjacent hot molecular cores and/or ultra-compact (UC) H II regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH II regions.

	Special Colloquium
Dr. Armin Rest	ORATED

STScI Baltimore

High-cadence rolling surveys, which continuously monitor patches of the sky (e.g., PS1, ZTF, ATLAS), have become standard among extra-galactic transient searches over the last two decades. These surveys have given us large statistical samples of supernovae (SNe) and other transients in the low-z range up to redshifts of 1. With JWST, going deeper and redder, we can now expand transient astronomy into the early, high-redshift universe, which offers us a direct approach for probing both the first stars and the epoch of reionization, as well as insights into rare high energy physics and explosion mechanisms (e.g., Pair-Instability SNe and Superluminous SNe). I will discuss our recent discovery of dozens of SNe up to z~5 with the JADES and COSMOS project, their spectroscopic follow-up, and what we can expect in the future with both JWST and Roman.

	Main Colloquium
Dr. Simon Ellingsen	CANCELED

University of Tasmania, Australia

Methanol is one of the most common molecules in the interstellar medium and I will give an overview of how methanol masers are being used to study the structure of the Milky Way and the physics of starbursts. Astrometric measurements of interstellar masers represent the most accurate way of determining the scale and structure of the Milky Way. Over the last 15 years significant progress has been made in measuring the number and location of Milky Way spiral arms in the northern hemisphere. Collecting equivalent data for the southern hemisphere has been very slow, primarily due to differences in available infrastructure. I will present some new results for 6.7 GHz methanol masers from the southern hemisphere made as part of the Sprals project. I will highlight recent upgrades to hardware and development of new calibration techniques which have enabled this and their application in other astrometry and astrophysics applications. A decade ago the first extragalactic class I (collisionally excited) methanol masers were detected in the nearby starburst galaxy NGC253. This are not scaled-up or extreme versions of Galactic class I methanol masers, but appear to trace regions where there are very large volumes of molecular gas undergoing low-velocity shocks. I will explain the prospects for using this new type of extragalactic maser to improve our understanding of early-stage starbursts. +++ Please note that this Main Colloquium takes place on a Wednesday to accommodate the speaker +++

	Main Colloquium
Dr. Reza Ayromlou	CANCELED

University of Bonn

TBD

	Special Colloquium
Nela Dvorakova	ORATED

Charles University in Prague

FS CMa type stars form a group of rare B type stars with extremely strong emission lines, show the presence of forbidden lines and a strong IR excess, pointing to a complex circumstellar environment of gas and dust. They are variable on timescales of days, months or even years. Binarity was the offered explanation for some of their observed properties. However, only some FS CMa stars are proven binaries. A promising lead was uncovered in the form of a strong magnetic field found in IRAS 17449+2320 discovered by Korcakova et al. (2022). Suggested by its unusually high space velocity, we are now pursuing a different scenario: a star-merger origin. Stellar mergers provide a natural explanation for such strong magnetic fields, the slow rotation of the FS CMa type stars as well as the presence of dust. Supporting evidence can be found in interferometric observations of HD 50138, which cannot be explained well with a binary model. Our analysis of a series of N-body simulations shows the importance of lower to intermediate mass mergers and how the B type stars provide an especially important channel of a merger formation.

	Special Colloquium
Nick Samaras	ORATED

Charles University in Prague

Milgromian Dynamics (or MOND) has been particularly successful in predicting scaling relations for galactic systems like the baryonic Tully-Fisher relation for spirals, the Faber-Jackson relation for ellipticals or the Radial Acceleration Relation. Despite the misconceptions regarding the presumed limitations of its theoretical development, MOND is actually able to provide a consistent cosmological scenario, explaining the FLRW expansion history, the CMB anisotropies and galaxy cluster dynamics. During this talk, I am going to present the so-called νHDM model, whose cosmogony relies on MOND with a light sterile neutrino of 11 eV rest-mass. The first-ever νHDM hydrodynamical simulations can potentially give rise to KBC-size voids and consequently tackle the Hubble tension. In a series of papers, the model is optimised based on the latest Planck data, hinting a distinct alternative road for cosmology.

	Special Colloquium
Dr. Sougata Sarkar	ORATED

Indian Institute of Science

Abstract: In astrophysics, it is well-known that there is a discrepancy between predicted and observed galaxy rotation curves. Observations show that the mass inferred from stars and gas is insufficient, leading to the concept of dark matter interacting gravitationally with baryonic matter. According to $\Lambda$CDM simulations, the NFW profile, with its cuspy nature, better matches the rotation curves of galaxies. However, observations of LSB and dwarf galaxies suggest a cored nature of dark matter halos, better described by cored profiles like pISO and Burkert. To model the dark matter halo of a galaxy, a common method involves fitting a tilted ring model to the 2D velocity fields derived from 3D data cubes. The tilted ring model represents a rotating disk galaxy as a series of thin, concentric rings, each moving at a constant speed. However, 2D-derived rotation curves are affected by systematic effects such as beam smearing and projection effects. Tools like FAT (Fully Automated Tilted Ring Fitting Code) can fit the tilted ring model directly to the 3D data cube, mitigating these effects. Earlier studies demonstrated that systematic effects can significantly impact the slope of the inner region of the dark matter profile. In our study, we have considered four dark matter halo profiles with varying shapes (cuspy, cored, and intermediate) for a pilot sample of eleven galaxies using 3D kinematic modelling from the GMRT archive atomic gas survey (GARCIA), covering a wide range of morphologies, mass range and other parameter values. These profiles include the NFW (Cuspy), pISO, Burkert (Cored) and Einasto (Intermediate) with a shape parameter $\alpha = 0.4$. In this talk, I will provide a brief overview of the GMRT archive atomic gas survey and highlight some of the scientific cases explored through GARCIA. I will then discuss the mass modelling of GARCIA-I.

	Main Colloquium
Prof. You-Hua Chu	ORATED

University of Illinois

30 Dor is the nearest archetypal giant HII region. Early low-resolution radio maps of 30 Dor region show three peaks that are designated as A, B, and C components. The A component is the main body of the 30 Dor giant HII region with the R136 cluster at its core, the B component hosts the OB association LH99 and a known supernova remnant (SNR), and the C component is a superbubble around the OB association LH90. The main component of 30 Dor is a bright source of diffuse X-ray emission but no SNRs have been identified and confirmed. Using archival HST images, deep Chandra X-ray observations, and ASKAP and MeerKAT radio observations, we are able to identify and confirm a SNR in 30 Dor A and identify shocked cloudlets in 30 Dor B. SNRs in 30 Dor are difficult to identify and confirm, but their influence is prevalent and obvious.

	Special Colloquium
Alessandra Corsi	ORATED

John Hopkins University

The births and mergers of neutron stars and black holes, the most exotic objects in the universe, can launch the fastest cosmic jets and power a variety of multi-messenger extragalactic transients. GW170817, the merger of two neutron stars witnessed through both its gravitational wave siren and its glow at all wavelengths of light, has marked the beginning of a golden age in multi-messenger astrophysics. Starting from the example of GW170817, I will show how observations at radio wavelengths can probe the ejecta and environments of compact binary mergers and help unveil their progenitors and remnants. I will then discuss opportunities and challenges ahead, as new observational facilities will transform a trickle of multi-messenger discoveries into a flood. I will conclude by highlighting prospects for extending the reach of multi-messenger studies to a variety of astrophysical sources ranging from stellar-mass compact objects born in core collapses to the heaviest black holes in merging galaxies.

	Promotionskolloquium
Jan Roeder	ORATED

MPIfR

The heart of every galaxy in the universe is home to an awesome monster: a supermassive black hole (SMBH). With masses millions to billions of times that of our sun, they are among the most powerful sources of energy in the Universe. They are surrounded by hot, magnetized plasma, some of which has the unfortunate fate of being accreted and swallowed by the black hole. A small fraction, however, is rescued by magnetic fields – and is ejected thousands of light years into interstellar space, in the form of highly collimated relativistic jets. Such an SMBH-powered system is known as an active galactic nucleus (AGN). Altough AGN have been the subject of active research for almost a century, many aspects of their inner workings remain obscure. In my PhD thesis, I addressed three specific questions, ranging from the very vicinity an SMBH to the far extended jets of AGN: What is the nature of the SMBH at the center of the Milky Way? What is the origin of the observed gamma-ray emission from AGN, and specifically the quasar 3C345? And lastly, how general is our is our established description of AGN as a whole? I have tackled these questions from both an observer's side, using very long baseline interferometry (VLBI) observations of AGN, and from a theorist's side - using general-relativistic hydrodynamics (GRMHD) simulations of exotic black holes and their surroundings. Zoom passcode: 3C345

	Promotionskolloquium
Petra Benke	ORATED

MPIfR

Active galactic nuclei (AGN) jets are the most luminous and energetic objects in the Universe, with many open questions regarding their formation, evolution and variability. In this talk, we will take a closer and closer look into the parsec-scale structure of these objects, using very-long-baseline interferometry (VLBI). I show first-light images from the 2.3 GHz monitoring of the TANAMI program, the only VLBI monitoring targeting southern-sky AGN. The 2.3 GHz monitoring was established to provide quasi-simultaneous data of the parsec-scale jets for the Fermi LAT, which lacks the resolution to probe the central region of AGN. I will then discuss a multiwavelength study of a gamma-ray flaring blazar and a radio multi-frequency observation of a nearby radio galaxy. Both of these shed light on jet variability and the similar physical processes which play a part in it, despite the two AGN being separated by billions of years of cosmic time.

	Special Colloquium
Dr. David Wiltshire	ORATED

Canterbury University, Christchurch, New Zealand

We present a general framework for solving Einstein's equations for stationary axisymmetric gravitationally bound differentially rotating matter distributions with internal pressure. A new quasilocal Newtonian limit is extracted for nonrelativistic relative velocities. The self-consistent coupling of quasilocal gravitational energy and angular momentum leads to a modified Poisson equation. The coupled equations of motion of the effective fluid elements are also modified, with quasilocal angular momentum and frame-dragging leading to novel dynamics. The phenonomenology of collisionless dark matter for disc galaxies is reproduced, offering an explanation for their observed rotation curves. Halos of abundant cold dark matter particles are not required. A full class of exact solutions is found in the general case of negligible internal pressure. A new geometrical structure is found- the rotosurface - which provides a rigorous general relativity answer to the question: where is infinity? The Milky Way's rotosurface leads to new astrophysical predictions, including possible synchrotron radiation from diffuse charged particles at 500-700 kpc from the galactic centre.

	Main Colloquium
Dr. Ramesh Bhat	ORATED

Curtin University

From the first high-quality detections of Crab giant pulses at frequencies below 300 MHz using the early prototype system that was comprised of merely three tiles, to recent successful launch of an ambitious, all-southern-sky pulsar survey using the Phase II compact array, pulsar science with the Murchison Widefield Array (MWA) has been through quite a long and exciting journey. Considering the highly non-traditional path dictated by the voltage capture system for high-time resolution science with the MWA, and the enormous data management, processing and software development tasks involved in facilitating and extracting science using such a capability, this has been a significant step forward. I will present an overview of some key milestones, highlighting examples of new science they have enabled, and commenting on the enormous science potential that can now be realized through ongoing large programmes such as the SMART (Southern-Sky MWA Rapid Two-meter) survey. I will also briefly remark on the yet-untapped potential for the MWA to become a powerful low-frequency monitoring telescope for pulsars and fast transients, once geared up with a real-time beam-forming capability to support high time resolution science applications.

	Special Colloquium
Dr. David Wiltshire	ORATED

Canterbury University, Christchurch, New Zealand

The timescape cosmology returns to first principles, with quasilocal gravitational energy replacing dark energy, to explain apparent cosmic acceleration. As inhomogeneities grow, they back react on average cosmic expansion, which differs from conventional FLRW models. Crucially, dynamical spatial curvature arises as time-varying gradients of the kinetic spatial curvature, and depends directly on the void volume fraction. The first investigation of void statistics in cosmological simulations in full general relativity, without lambda, now supports this. The timescape expansion history is close to lambdaCDM, but with differences at a precision which we are now finally probing. Whereas lambdaCDM is increasingly challenged - independent observational tests now favour timescape - some with strong Bayesian evidence. I will survey these results, open questions, current limitations, and possible future tests.

	Special Colloquium
Dr. Zhiqiang Yan	ORATED

Nanjing University, China

The element compositions of resolved stars formed at distinct epochs record the chemical evolution trajectory of a galaxy. As this evolution is influenced by the galaxy-wide stellar initial mass function (gwIMF), the abundance profiles of stars offer a means to estimate the gwIMF. In this presentation, I will demonstrate the application of this methodology using the dwarf galaxy Sculptor as a case study. Specifically, I will elucidate how the gwIMF of long-lived low-mass stars intricately shapes the observed stellar metallicity distribution of a galaxy, thereby allowing for the estimation of low-mass gwIMF via galaxy chemical evolution modeling. Our analysis suggests that dwarf galaxies, characterized by low stellar metallicities and low star formation rates, exhibits a shallower gwIMF slope for low-mass stars and a steeper gwIMF slope for massive stars (bottom- and top-light IMF). Furthermore, we have compared our findings with those derived from independent IMF estimation techniques including stellar population synthesis and star counting, illustrating a coherent and systematic IMF variation. This will be a relatively short colloquium, discussions are encouraged.

	Promotionskolloquium
Santana Mansfield	ORATED

Uni Bonn

Stellar exotica are unusual stars or binary systems which are distinctive due to variability in their brightness, or by their emission in the ultraviolet and X-ray wavelengths which indicate high energies. These stars and systems demonstrate some of the most ferocious physics known to astronomy, such as colliding stars, mass accretion and nova explosions. Some stellar exotica form due to the interactions between binary components, for example blue straggler (BS) stars, cataclysmic variables (CVs) and X-ray binaries. Others show fluctuations in their luminosities from instabilities in their interiors, such as RR Lyrae variables and M-dwarf stars undergoing the convective kissing instability (CKI). In this talk I will describe some of these interesting stellar exotica and show how they can be found in globular clusters and investigated with stellar evolution modelling.

	Promotionskolloquium
Joscha Jahns-Schindler	ORATED

MPIfR

Fast Radio Bursts (FRBs) are fascinating flashes of radio waves stemming from distant galaxies. Recently discovered, their origins are still mysterious. Most FRBs only appear for the split second of their duration and are not found again, while about 5% of FRB sources emit bursts repeatedly. Even though the origins are unclear, FRBs are the first extragalactic, short-duration radio signals, which makes them a unique probe of the Universe. In this talk, I will present my thesis, which aims to gain a better understanding of FRBs and to develop FRBs as tools for cosmology. I used the 305-m Arecibo Telescope to address the unknown nature of FRBs. The target, FRB 121102, is the longest known and one of the most active repeating FRBs. The search yielded 849 bursts in ten observations, one of the largest set of bursts, including the highest burst rate as yet. The analysis of burst arrival times revealed a characteristic separation time. A novel model of the burst spectra led to a new spectro-temporal effect, providing a new diagnosis for emission models. A challenge to use FRBs as tools is the joint influence of several cosmological quantities, the Hubble constant and the baryon density in the Universe. To break the degeneracy, I present a new Bayesian framework. This framework exploits a proposed connection between FRBs and gravitational waves. Through the framework, future associated gravitational waves can be combined with FRB observables to untangle the different parameters.

	Special Colloquium
Dr. Vicente Villanueva	ORATED

Universidad de Concepcion

We study galaxy samples representative of the local (EDGE and VERTICO surveys) and early universe (CRISTAL survey), combining interferometric CO, [CII], dust-continuum data and IFU optical spectroscopy. We focus on the radial dependence of the star formation (SF) efficiency of the total gas on morphological, structural, and dynamical properties of the galaxies. We test the impact of environmental processes on galaxies from the Virgo cluster. Our results show that the cluster environment not only affects the outskirts of galaxy disks and their atomic gas, but deeply changes the distribution and efficiency of the centrally located molecular gas component. We study the onset of SF quenching by investigating a sample which encompasses main sequence (MS), green valley (GV), and red cloud (RD) galaxies. We note that GV galaxies have lower molecular SF efficiencies than galaxies on the MS, particularly within galaxy centers. We also present new [CII] 158 um and dust continuum observations of HZ10, a dusty MS galaxy system at z=5.66. Our results suggest that the UV emission (likely from young stellar populations) is strongly affected by dust attenuation in the more dusty components of the HZ10 system.

	Special Colloquium
Dr. Yosuke Mizuno	ORATED

Shanghai Jiao Tong University

Sgr A* exhibits flares at various wavelengths, but their origin remains unclear. Magnetic flux rope eruption from the black hole is one of the possible candidates for explaining the observed Sgr A* flares. Based on new 3D GRMHD simulations of magnetized accretion flows, we investigate the dynamics of magnetic flux rope ejected from the vicinity of the black hole. We found the formation of magnetic flux ropes strongly depends on the size of the magnetic loops. We also calculate the emissions from the magnetic flux ropes. From the non-thermal emission models, we can reproduce the observation of near-infrared flares and broadband spectral energy distribution (SED). We also discuss the polarization signatures of the Sgr A* flare.

	Special Colloquium
Bram van den Berg	ORATED

Radboud University

Traditionally, black hole parameter estimations have been performed manually, a time-consuming process that does not guarantee optimal results. At Radboud University, we have developed an advanced parameter estimation framework that integrates simulations, such as General Relativistic Magnetohydrodynamics (GRMHD) and General Relativistic Radiative Transfer (GRRT), with a nested sampling algorithm. This new approach has led to the creation of an efficient and easy to use fitting program that utilizes observational images, spectral energy distributions (SEDs), and coreshift spectra to achieve accurate parameter estimations.

	Special Colloquium
Dr. Sean Ressler	ORATED

University Toronto

I will summarize recent results on jet precession in thick accretion flows relevant for Sgr A*, M87, and other low luminosity AGN. These include results from wind-fed simulations of Sagittarius A*, results from more general simulations of misaligned disks, and results from simulations of binary black hole systems. I will argue that while Lense-Thirring-type precession is generally not seen in these simulations, there are other effects that may appear very similar observationally, at least for relatively small precession angles (~ 10 degrees). On the other hand, spin-orbit coupling between a lower mass binary black hole companion's orbit and the central supermassive black hole can produce significant jet precession (~ 60 degrees) even when there is not necessarily a clear signal of the companion in other emission measurements. Because of this, if relatively large amplitude, consistent precession is observed in jets associated with radiatively inefficient AGN, it may be strong evidence of a hidden binary companion.

	Special Colloquium
Dr. Alejandro Mus	ORATED

Univierstia degli Studi di Cagliari

In this talk, I present new frameworks for mm-VLBI data analysis, which include 1) A scattering mitigation framework for dynamic imaging of time-variable or static objects and 2) A machine learning pipeline for transient detection in VLBI data. We expect the combination of the two frameworks would have a strong impact on a variety of science topics like the long period repeating transient searches. First, I introduce the advanced optimization techniques MOEA/D (Müller&Mus+2023, Mus&Müller+2024) and Particle Swarm Optimization (Mus+2024) whose flexibility allows the modeling for scattering mitigation based on Stochastic Optics (Johnson16).Then, I present results on synthetic movies at horizon scales, exploring different intrinsic structures, source evolution and scatteringparameters (like the screen distance, and speed). In a second step, I will show the performance of this framework at 86 GHz, by using synthetic Sagittarius A* (SgrA*) Global mm-VLBI Array(GMVA) data with various corruptions. We show that our algorithm can recover the intrinsic SgrA* ring and the scattering screen, thanks to the advantages of MOEA/D and PSO. Next, I will introduce a new machine learning pipeline for detecting transients in VLBI data. Very recently, pulsars with unexpected low period have been found (for instance Caleb+2022,2024,Hurley-Walker+2023). We aim to revisit old data using our fast and unsupervised algorithm to try to detect hidden slow transient. Finally, I will talk about ongoing work using full bandwidth capabilities aim to mitigate scattering at lower frequencies, helping the transient search with novel telescopes like next-generation VLA.

	Special Colloquium
Dr. Felix Thiel	ORATED

Queen University Canada

Very Long Baseline Interferometry (VLBI) is a technique in radio astronomy commonly used to image radio galaxies and their central black hole shadows at extremely high resolution. The resolution of ground-based VLBI however is limited both in baseline and observing frequency by the size of the Earth and molecular absorption of the atmosphere resepectively. While space missions are extremely costly, balloon-borne VLBI would give access to frequencies beyond those of the Event Horizon Telescope (EHT) at a fraction of the cost. As a first proof of concept for balloon-borne VLBI, the Balloon-borne VLBI Experiment (BVEX) will launch as part of the Canadian Space Agency (CSA) Stratos program from Timmins, Ontario, Canada in August 2025 and will operate above 99% of the Earth's atmosphere. This experimet consists of a K-band 22 GHz radio telescope and receiver, where the singals will be correlated with a large ground-based telescope. In this talk I will give an overview of the telescope, receiver and backend as well as technical challenges such as position tracking and timing reference stability that arise when attempting VLBI from the stratosphere. To wrap up, I will talk about how lessons learned from BVEX will help in designing a mm/sub-mm VLBI mission in the future, which could improve the uv-coverage of VLBI networks such as the EHT or next-generation EHT (ngEHT).

	Master Colloquium
Lennart Böhm	ORATED

MPIfR

With the origin of chlorine presumed to be in core-collapse supernovae, stellar models predict the ratio of its two stable isotopes 35Cl/37Cl, between 1 and 4, but observations of Cl-bearing molecules have been limited due to their high-lying transitions. I will present observations of the HCl (1–0) line at 625 GHz, carried out using the SEPIA660 receiver on the APEX telescope. We detected both isotopes of HCl toward 27 Galactic sources, spanning a range of galactocentric radii, doubling the number of sources toward which it has previously been detected. Toward 11 sources we see pure emission with hints of an outflow wing while the remaining sources display complex profiles with both emission and absorption. In addition, the HCl detected in absorption toward NGC 4945, the first detection of this species in a nearby galaxy. For the Galactic sources, we obtained an isotopic ratio between 2.0 and 2.6 with an average value of 2.2+/-0.2. Further, we performed a radiative transfer analysis using RADEX with recently computed collisional rate coefficients between HCl and H2, which constrained HCl-bearing gas to trace warm, dense gas in the core and hot, translucent gas in the outflow.

	Special Colloquium
Dr. Zhiqiang Yan	ORATED

Nanjing University, China

Our study utilizes stellar mass measurements of the most massive stars in resolved young (< 5 Myr) star clusters to illustrate statistically that star formation follows a highly regulated process, distinct from stochasticity. This unveils constraints and a novel approach for sampling stellar masses in hydrodynamical simulations of both star clusters and galaxies. Additionally, we validate our hypothesis by integrating the empirical Initial Mass Function (IMF) for star clusters, enabling the calculation of variations in the galaxy-wide IMF. The expected systematic variations of the galaxy-wide IMF are subsequently confirmed through galaxy photometry and evolutionary models. This will be a relatively short colloquium, discussions are encouraged.

	Master Colloquium
Vanessa Pinto	ORATED

MPIfR

In Very Long Baseline Interferometry (VLBI), calibration and imaging are strongly associated with each other. The traditional CLEAN algorithm has served as the defacto tool for tasks such as imaging, self-calibration, and polarization calibration. However, CLEAN suffers from limitations such as restricted final image resolution, lack of uncertainty quantification, and difficulty incorporating prior knowledge. As a result, alternative approaches, such as the Bayesian inference software resolve, have emerged as a method that outperforms CLEAN. This project aims to utilize resolve to overcome the limitations of CLEAN and specifically, to demonstrate the process that combines self-calibration and imaging for multiple sources simultaneously. We employ survey data for 38 target sources at 15 GHz drawn from the MOJAVE catalog. This approach allows us to generate high-resolution reconstructed images for each target source as well as joint antenna gain plots. A comparative analysis of images produced by resolve and CLEAN will highlight the improvement in resolution achieved with resolve. Furthermore, this project emphasizes the efficiency achievable through resolve’s automated approach for combining self-calibration and imaging for multiple sources.

	Master Colloquium
Lena Debrecht	ORATED

MPIfR

Blazars are powerful active galactic nuclei (AGN), which exhibit energetic jets pointing at a small angle to the observer. Understanding the formation and motion of these jets requires high-resolution observations. In this study we analysed three epochs of the blazar NRAO 150 (redshift z=1.52) observed with the Global mm-VLBI Array at 86 GHz and one epoch observed with the EVN at 22 GHz and 43 GHz. The aim of this study is to probe the jet's morphology via total intensity imaging and to model its kinematic behaviour. As the source points at a small angle to our line of sight, geometric projection effects need to be taken into account, which can alter the appearance of emission features. Within this work we examined a new kinematic model for NRAO 150 and fitted a helical model to the jet feature's trajectory. We tracked two emission features through all three epochs and report the detection of a counter-clockwise jet rotation for NRAO 150. The computed projected angular velocities are (–41.93 ± 11.80) deg/yr and (20.45 ± 14.19) deg/yr, and the projected radial velocities of (0.01 ± 0.01) mas/yr and (0.01 ± 0.02) mas/yr. We examined possible kinematic scenarios taking into account projection effects and interpreted how they relate to the observed jet features.

	Main Colloquium
Dr. Nadine Neumayer	ORATED

Max-Planck-Institut für Astronomie, Heidelberg

The centers of massive galaxies are special in many ways, not least because apparently all of them host supermassive black holes. Since the discovery of a number of relations linking the mass of this central black hole to the large scale properties of the surrounding galaxy bulge it has been suspected that the growth of the central black hole is intimately connected to the evolution of its host galaxy. However, at lower masses, and especially for bulgeless galaxies, the situation is much less clear. Interestingly, these galaxies often host massive star clusters at their centers, and unlike black holes, these nuclear star clusters provide a visible record of the accretion of stars and gas into the nucleus. I will present our ongoing observing programme of the nearest nuclear star clusters, including the Milky Way Center, and the stripped galaxy nuclei omega Centauri and M54. These observations provide important information on the formation mechanisms of nuclear star clusters, allow us to measure potential black hole masses and give clues on how black holes get to the centers of galaxies.

	Special Colloquium
Prof. Dr. Fatemeh Tabatabaei	CANCELED

MPIA

Studying the radio spectral energy distribution (SED) of distant galaxies is essential for understanding their assembly and evolution over cosmic time. We present rest-frame SEDs of a sample of star-forming galaxies at z< 5 in the COSMOS field as part of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) project. MeerKAT observations combined with archival VLA and GMRT data allow us to estimate the equipartition magnetic field and calibrate star formation rate (SFR) up to z=5. We also measure the total energy budget of high-z galaxies emitting in the mid-radio continuum (MRC bolometric luminosities) at 1.5

	Main Colloquium
Prof. Dr. Felix Aharonian	CANCELED

DIAS/Dublin and MPIK/Heidelberg

TBD

	Main Colloquium
Dr. Roberto Neri	ORATED

IRAM Grenoble (France)

NOEMA was designed and built to provide world-class observing capabilities to a global community of thousands of researchers. Equipped with twelve 15-meter antennas, state-of-the-art receivers, and baselines extending up to 1.7 kilometers, NOEMA delivers a comprehensive suite of capabilities. These features ensure that NOEMA remains at the forefront of astronomical research, consistent with IRAM's long-term development strategy. In my presentation, I will outline NOEMA’s current operational capabilities and the planned upgrades in the near future. Additionally, I will highlight some of the recent scientific discoveries and achievements facilitated by NOEMA.

	Main Colloquium
Prof. Dr. Selma de Mink	ORATED

MPA

The majority of stars form in binary and multiple systems. To understand the lives and final fates of stars we need to understand how the presence of companions can affect their lives. This is especially true for massive stars we think that the majority interact with its binary companion and more than a fifth can even interact with the third star. These questions are especially timely now in the era of gravitational wave detections which are starting to reveal the properties binary black holes and neutron stars. At the same time large stellar surveys, in particular Gaia, are probing these multiple systems, Tess and soon PLATO are uncovering stellar oscillations that allow us go probe the interior of these stars, time domain surveys catch the more dramatic events involving mergers, disruptions and explosions. I like to discuss a few fun and possibly important new insights in massive (binary) stars that we have been pursuing at the new stellar department at the Max Planck Institute for Astrophysics in Garching near Munichm Germany. This will include a discussion of the claims that the Red Supergiant Betelgeuse is rotating, why the widest binaries are not boring at all, the elusive stripped stars that were missing and have now been found and if time permits a discussion about Blue Supergiants.

	Promotionskolloquium
Jonah Wagenveld	ORATED

MPIfR

The cosmic radio dipole is an anisotropy in the number counts of radio sources, analogous to the dipole seen in the cosmic microwave background (CMB). Measurements of the radio dipole with large radio surveys have shown that though the radio dipole is aligned in direction with the CMB dipole, the amplitudes are in tension. These observations present an intriguing puzzle as to the cause of this discrepancy, with a true anisotropy having large repercussions for cosmology as a whole. Measurements of the cosmic radio dipole with large radio surveys have often suffered from systematics in the data, hampering sensitivity and reliability of these measurements. In this thesis, I aim to measure the cosmic radio dipole with the MeerKAT Absorption Line Survey (MALS). Though sky coverage of MALS is low, with 391 pointings observed in total, the sensitivity and field of view of MeerKAT yields thousands of sources observed in each pointing. We perform a deep analysis of the complete set of processing steps, from observations to cataloguing, of ten MALS pointings, to characterise and quantify potential systematic effects which could hamper a dipole measurement. Using the noise characteristics of these pointings, we find that we can homogenise the catalogues to a deep enough level for a dipole measurement. We furthermore define Bayesian estimators that are able to perform a dipole measurement with the sparse sky coverage of MALS. Testing these estimators out on other radio surveys, we perform the most significant measurement of the cosmic radio dipole yet. Finally, we perform a measurement of the dipole using all MALS pointings, but find an effect in the data which causes a systematic variation in source density with declination, hampering a dipole measurement. Though we can account for the effect by extending our estimators, it comes at the cost of further uncertainties, which can only be remedied by reprocessing the data. However, combined with other measurements performed in this thesis and in the literature, there is a little doubt anymore as to the legitimacy of the radio dipole measurement, and we may look forward to further measurements which aim to uncover the cause of the dipole tension.

	Special Colloquium
Prof. Richard Lieu	ORATED

University of Alabama in Huntsville

The basic properties of radio time series from a stationary source as governed by Bose Einstein statistics are considered in the classical limit, with a view to deriving the radiometer equation. Three immediate consequences are discussed. First is the prospect of significantly increasing the S/N of transient detection by means of a set of orthogonal digital filters, or eigenfilters. Second is the imprint of source acceleration in the voltage autocorrelation function. Third is the imprint of dispersion on the phase of single modes of radiation which could be recovered by averaging over the phases of many modes w.r.t an epoch phase.

	Special Colloquium
Prof. Dr. Natasha Hurley-Walker	ORATED

Curtin University

The long-period radio transients are a newly-discovered class of Galactic radio sources that produce pulsed emission lasting tens of seconds to several minutes, repeating on timescales of tens of minutes to hours. Such cadence is unprecedented, and there is currently no clear emission mechanism or progenitor that can explain the observations, which include complex polarisation behaviour, pulse microstructure, and activity windows that range from hours to decades. Could they be ultra-long period magnetars, and connected to the phenomenon of Fast Radio Bursts? Could they be white dwarf pulsars, defying the expectations of the magnetic field evolution of these stellar remnants? In this talk I will review the discoveries made so far, including recent new detections with the Murchison Widefield Array and the Australia SKA Pathfinder. I’ll examine informative simulations of their evolution, the potential physical explanations, and the prospects for detecting more of these sources in ongoing and upcoming radio surveys, that will help uncover their true nature.

	Main Colloquium
Dr. Sergei Tsygankov	ORATED

Turku University

Analysis of the polarization of electromagnetic radiation, or polarimetry, is a unique tool that allows us to obtain information about astrophysical objects that cannot be obtained in other ways, for example, regarding their geometry. With the launch of the IXPE (Imaging X-ray Polarimetry Explorer) mission at the end of 2021, this instrument became available in the X-ray range as well. In my talk I will give a brief overview of the results obtained during the first two years of IXPE observations of accreting neutron stars, mainly focusing on the highly magnetised ones (X-ray pulsars, XRPs). It was found that in all observed XRPs, the measured value of the degree of polarization is below 15%, which is much less than the theoretically predicted values. In some pulsars, it was possible to study in detail the variations in the degree of polarization and the polarization angle as a function of the rotation phase of the neutron star, which, in turn, made it possible to determine the geometric parameters of the system. I will discuss the physical mechanisms that could potentially explain the unexpected polarization properties observed in XRPs.

	Special Colloquium
Prof. Dr. Jongho Park	ORATED

KyungHee University

GPCAL is an automated pipeline for instrumental polarization calibration of Very Long Baseline Interferometry (VLBI) data. The pipeline is designed to achieve high calibration accuracy by fitting the instrumental polarization model, including the second-order terms, to data from multiple calibrator sources simultaneously. It also allows for using more accurate linear polarization models of calibrators for D-term estimation, compared to the conventional method that assumes similar linear polarization and total intensity structures. This assumption has been widely used in existing packages for instrumental polarization calibration but could be a source of significant uncertainties when there is no suitable calibrator that satisfies the assumption. Furthermore, conventional software and pipelines have assumed that polarization leakages are constant over observing frequency and time, which is not always the case. The latter issue may be more pronounced in the GMVA, which has very small telescope beams and generally less antenna pointing accuracy. We have developed methods to calibrate the frequency- and time-dependent leakages in GPCAL. In this talk, I will briefly introduce GPCAL, the new methods, and their applications to real VLBI data sets. +++ this is an online conference. The meeting will be streamed in room 3.25 +++

	Special Colloquium
Lydia Haacke	ORATED

Swinburne University, Melbourne, Australia

Ultra-diffuse galaxies (UDGs) have been a hot topic for almost a decade now after their definition in 2015. They are dwarf galaxies in mass, extremely faint (μg,0 > 24 mag/arcsec2) and with effective radii comparable to giant galaxies (reff > 1.5 kpc). A curious aspect of their existence are the rich globular cluster (GCs) systems some of them host, much more than is typical for normal dwarf galaxies. GC systems are closely connected to their host's evolution and allow us to trace its chemical and dynamical properties. One of these globular cluster rich UDGs is NGC5846 UDG1. It has 54 GC candidates from HST imaging, 20 of which we have spectroscopically confirmed. With these, it is possible to compare the dynamics of the GC system to the stellar component of the galaxy and trace the total mass out to more than 1.5 effective radii. In this talk I will present the results of UDG1's GC system kinematics, the implications for its dark matter halo and the implications for GC-rich dwarf galaxies in general.

	Special Colloquium
Henriette Wirth	ORATED

Charles University, Prague, Czech Republic

While multiple populations distinguishable by their light-element content are well studied in many globular clusters (GCs), only recently iron spreads have been discovered in some of them. In this talk an analytical method to compute the number of core collapse supernovae (CCSNe) that must have contributed to this iron spread is presented. From this the duration of star formation during the initial stage of a GC's development can be computed. For a sample of 55 GCs with known iron spreads we find that the number of CCSNe required to explain the iron spread varies between a few and a few tens of thousands. This leads to a SF duration typically between 3.5 and 10.5 Myr.

	Main Colloquium
Prof. Dr. Leon Koopmans	CANCELED

Groningen University

Observations of the first luminous cosmic structures, with ground and space-based optical and infrared telescopes, are slowly lifting the veil on the complex physical processes that governed the Epoch of Reionization and Cosmic Dawn. These observations, most recently with JWST reaching redshift well into the Cosmic Dawn, however, are only the tip of the iceberg: islands in a sea of neutral hydrogen. I will review the current status of the LOFAR Epoch of Reionization Key-Science Program, presenting our latest improved power-spectrum limits on the 21-cm signal of neutral hydrogen, the constraints it sets on the high-redshift IGM, and present several breakthroughs in our understanding of the data itself, which will be crucial for the future SKA. I will also show the latest results from the NenuFAR Cosmic Dawn Key-Science Program, which aims to measure the 21-cm signal during the Cosmic Dawn. I will place these results in context of SKA and our plans to push towards 21-cm cosmology of the Dark Ages using space-based receivers, such as ALO, currently a pre-phase-A concept for a radio telescope to be placed on the lunar farside by ESA's Argonaut landers.

	Special Colloquium
Helena Faustino Vieira	ORATED

Cardiff University

The question of whether star formation (SF) is directly affected by the large-scale dynamics within a galaxy, or merely dependent on the local conditions of the interstellar medium (ISM), is a matter of long-standing debate. This is hindered by the difficulty in simultaneously probing the small-scales associated with the SF process, and the large-scales which might regulate the formation and evolution of molecular clouds, where stars form. Therefore, significant advancement can only be achieved with high-resolution imaging of entire galaxies, such that the inner properties of molecular clouds are resolved whilst maintaining the galactic context. I present here our work on studying the resolved properties of the ISM by exploiting the high-resolution data from HST in nearby spiral galaxies to its full potential, which is highly complementary with new JWST data. I will showcase how, with a newly developed technique to derive dust extinction using optical HST data, we can retrieve maps of the dust (and gas) content across entire galaxies at unprecedented resolution. For our sample of nearby galaxies, our maps have resolution corresponding to a few parsecs, allowing us to study the extragalactic ISM with a level of detail typically only achieved with Galactic studies. Our study of M51 using this technique has shown that there are clear changes in the properties of the ISM depending on the galactic environment as well as on the type of spiral potential felt by the gas.

	Special Colloquium
Nikos Mandarakas	ORATED

Institute of Astrophysics - FORTH, Crete, Greece

Optical polarimetry has traditionally served as one of the primary probes of the interstellar medium (ISM). With recent advancements in measuring stellar distances and mapping dust in different lines of sight, polarization measurements are now more essential than ever as we are transitioning into the era of 3D magnetic tomography. Therefore, it is now imperative to update our tools and techniques. I will discuss recently achieved milestones of optical polarimetry regarding 3D magnetic tomography, and present evidence for the need to revise the heavily used Serkowski formula.

	Main Colloquium
Prof. Heinz Andernach	ORATED

Th"uringer Landessternwarte, Tautenburg, Germany, on leave from University of Guanajuato, Mexico

Giant Radio Galaxies (GRGs) with a projected linear extent over 1 Mpc were first found in 1974, and over 5,000 are now known, plus another 5,000 larger than 0.7 Mpc, the currently adopted threshold for GRGs. I present results based on my compilation of GRGs (a) from literature, and my own visual inspection of (b) large-scale radio surveys in general (e.g. NVSS, SUMSS, RACS, LoTSS DR2, etc.), and of specific regions like (c) the LoTSS Deep Fields (LDF), as well as (d) the equatorial SWAG-X/eFEDS/LOFAR field. Although very time-consuming, systematic visual inspection clearly provides a higher ratio of GRGs <1 Mpc to those >1 Mpc than literature samples, which tend to disfavor smaller GRGs. I also show examples of published mis-identifications based on automated algorithms, lacking the necessary human control of the results. In order to shed light on the open question why GRGs can reach their large sizes, I look at (a) their location as function of environment density in the LDF and SWAG-X fields, and (b) I select the very largest 115 GRGs (from 3 to 6.6 Mpc), to study how they were discovered (mostly by LOFAR), their distribution in redshift and radio luminosity, and their bending angle, and compare these with GRGs of more modest sizes.

	Special Colloquium
Rashid Mohammed	ORATED

Indian Institute of Science, Bangalore, India

The physical conditions of the interstellar medium (ISM) profoundly influence the star formation activity of galaxies. However, the exact role of the physical properties of ISM is yet to be understood in regulating star formation. Hence, it is crucial to constrain these properties through observations in the star-forming regions. The famous Orion HII region is one such region hosting a variety of objects, e.g., young star clusters, predominantly atomic photodissociation region (PDR), and layered ionized gases. Moreover, its proximity (414 ± 7 pc) makes it an ideal target for studying vital properties of the ISM in star-forming regions and physical processes happening in them. HII regions dominantly emit radiation through thermal mechanisms. However, a handful of HII regions are reported to emit nonthermal emissions. Recent studies have made efforts to explain such atypical nonthermal emissions through physical models. However, such observational results are fairly new and yet to be understood clearly. Using the enhanced capabilities of the upgraded Giant Metrewave Radio Telescope (uGMRT), we have studied the ISM in the Orion region. In this talk, I will present the results of the wide-band observations of the Orion nebula at unique low-frequency bands of uGMRT. From deep continuum images of band-3 (300 MHz – 500 MHz) and band-4 (635 MHz – 735MHz) of uGMRT, we have produced a reliable spectral index map. We are reporting indications of nonthermal emission from some parts of the region. To establish the reliability of the spectral index map, we are also validating the reliability of the spectral map produced through simulated data of uGMRT. I will also discuss how the stellar winds from the massive stars residing in the massive star clusters of the Orion nebula may give rise to such physical scenarios to explain this new finding.

	Promotionskolloquium
Moritz Haslbauer	ORATED

Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn

Investigating the current standard model of cosmology (Lambda Cold Dark Matter - LCDM - framework) by performing tests on different astrophysical scales could indicate if the missing mass problem implies indeed the existence of cold dark matter (CDM) or rather emerges because of a breakdown of Newton's law of gravity. In my talk, I will argue that the performed tests during my doctoral studies disprove the LCDM framework over all probed scales ranging from galactic to large-scale structures. The tests established a consistent picture of the Universe in which dynamical friction on galactic scales is next to absent and structure formation is more enhanced than predicted by the LCDM framework disfavoring the existence of CDM on galactic scales and pointing to a long-range correction of Newtonian gravity as provided by Milgromian Dynamics (MOND). Recent observations of high-redshift galaxy candidates by the James Webb Space Telescope illustrate that testing cosmological models requires also assumptions about the underlying stellar initial mass function (IMF) which seems to depend on the global star formation rate and metallicity. As the interpretation of photometric measurements depends on the properties of the stellar IMF, I will discuss that galaxy evolution and cosmological models have to be considered in a more holistic picture by bridging stellar population of galaxies with cosmology. [Referees: Prof. Dr. Pavel Kroupa, Prof. Dr. Karl Menten, PD. Dr. Akaki Rusetsky, Prof. Dr. Estela Suarez]

	Lunch Colloquium
Janhavi Baghel	ORATED

National Center for Radio Astrophysics, Pune, India

Blazars are active galactic nuclei (AGN) with jets oriented at small angles to our lines of sight that result in their extreme properties due to Doppler boosting effects. They are delineated based on their spectral properties into quasars and BL Lac objects. The underlying reasons for this blazar divide are not ambiguously clear. In this talk, I will present polarization sensitive data from the VLA and GMRT on the Palomar Green (PG) blazar sample. These data reveal differences in the kiloparsec (kpc) scale jets between the blazar subclasses. The PG quasars show a great diversity in their morphology not always consistent with their purported parent sample of FRII radio galaxies. While many BL Lacs exhibit core-halo morphology consistent with FRI radio galaxies, some possess FRII-like hotspots. Overall, polarimetric observations reveal differences in the inferred magnetic fields in the kpc-scale jets of blazars that may be the result of intrinsic differences in accretion disk structures along with extrinsic differences in their surrounding environments.

	Main Colloquium
Prof. Dr. Selma de Mink	CANCELED

MPA

+++postponed+++

	Main Colloquium
Dr. Jacques Roland	ORATED

Observatoire de Paris

Variations of the flux density of the nucleus of an extragalactic radio source can be due either to the variations of the synchrotron spectra of the black holes contained in the nucleus, or to the ejection of VLBI components. As a consequence of the variations of the synchrotron spectra of the black holes, there will be periods during which the low frequency and the high frequency observations will be aligned on the same BH, say BH1, and periods during which the low frequency and the high frequency observations will be aligned on different BHs, say BH1 and BH2. We obtained centroid position time series at 15 GHz from MOJAVE model fitting giving epoch positions of the VLBI components and for each epoch, we calculated the 15~GHz flux barycenter positions using a beam $B = 2$ mas which corresponds to the $8$~GHz beam. The comparison of the $8$~GHz and $15$~GHz time series shows that: a) the time series are generally correlated, but they can be anti-correlated during some periods and b) the absolute position of the ICRF3 survey corresponds to the mean position of the $15$~GHz flux density barycenter within $\leq 0.100$ mas$. The comparison of the $8$ and $15$~GHz has been done for 2201+315 which structure of the nucleus is known and for 0851+202 and 0923+392 which structures of the nucleus are not known.

	Special Colloquium
Prof. Dr. Tom Megeath	ORATED

The University of Toledo

Protostars play an important role in cosmic evolution. It is during the protostellar phase that most of a stars mass is accreted, and feedback driven by this accretion is thought to lower the star formation efficiency and shape the IMF. Outflows from protostars also help regulate star formation in molecular clouds. Finally, the material for planet formation is assembled into disks during the protostellar phase.  I will present current results from the IPA (Investigating Protostellar Accretion) program which is studying five protostars across the mass spectrum at 2.9-28 microns with the JWST IFUs. These data probe both the feedback from young stars and the chemistry of ices on dust grains. I will overview how JWST, combined with ALMA and time-domain IR data, can probe the complicated network of processes in protostars, from several thousand au to stellar scales. I will then present the forthcoming HEFE large program on JWST, and discuss the future potential of the observatory to study galactic star formation.

	Main Colloquium
Prof. Thorsten Kleine	ORATED

Max Planck Institute for Solar System Research

Earth contains several oceans of water. Determining the origin of this water is key not only for understanding how Earth formed, but also for identifying the processes that made it a habitable planet. In general, Earth may have accreted water from its main building material or from an exotic source that otherwise contributed little mass to Earth. In this talk I will show how meteorites, left-over fragments from the earliest stages of planet formation, can be used to distinguish between these two possibilities and thus help to reconstruct how and from where Earth accreted its water.

	Special Colloquium
Prof. Dr. Bhaswati Mookerjea	ORATED

Tata Institute of Fundamental Research (TIFR)

The Space Applications Centre (SAC) of the Indian Space Research Organization (ISRO) has successfully designed and developed the critical components for the first Indian sub-millimeter telescope. The observatory will be located initially at the 4500 m Hanle site of the Indian Astronomical Observatory and will be a partnership of ISRO withe Indian Sub-millimeter-wave Astronomy Alliance, which is a partnership of scientists from leading Indian astronomy, physics and space research institutions. The 6-m telescope in the first phase will be equipped with a dual band receiver at 230--345 GHz and will be used for the studies of the neutral interstellar medium. The observatory by virtue of its longitudinal position has the potential to be a new location for the Event Horizon Telescope (EHT). The Himalayan sites are among a small number locations globally, that have sufficient atmospheric transmission to allow observations in the sub-millimeter wavelength bands, at frequencies of about 200-500 GHz and higher. In this talk, I will present the current status of the Indian sub-millimeter observatory as well as the ongoing and future work on the characterization of the Himalayan sites for sub-millimeter astronomy.

	Special Colloquium
Dr. Mark Walker	ORATED

Manly Astrophysics, Australia

In astronomy, solid hydrogen has been largely ignored for over 50 years. That was a mistake. It came about because the pure solid was shown to sublimate rapidly under interstellar conditions; but in the ISM solid H2 is expected to become electrically charged, and the electric field suppresses sublimation. I will argue that the spectroscopic properties of interstellar dust make a strong case in support of solid H2 being a major dust component. In turn, that suggests that our Galaxy possesses a substantial reservoir of dark gas clouds - hydrogen "snow clouds". I'll describe a new picture of the physics of interstellar scattering of radio waves, based on the tidal disruption of H2 "snow clouds" by stars. Somewhat surprisingly, that work has also led us to a beautiful new model of the rare, but spectacular, R Coronae Borealis stars.

	Promotionskolloquium
Timea Kovacs	ORATED

MPIfR

Magnetic fields play an important role in galaxy evolution, from processes such as gas dynamics and star formation to galactic outflows. However, the redshift evolution of galactic-scale magnetic fields is not well constrained, both observations and theoretical predictions are lacking, with only a handful of direct magnetic field strength measurements in distant galaxies. In my talk, I will present my results from both radio polarimetric observations and synthetic observations made with the IllustrisTNG50 simulation. First, I will present the analysis of broadband (1 - 8 GHz) spectro-polarimetric Very Large Array observations of two lensing systems (B1600+434 and B0218+357). Using these, we measured the halo magnetic field of a distant galaxy at z=0.414 (corresponding to 4.4 Gyr ago) for the first time with a strength of 1.2 - 1.8 uG, and found an axisymmetric disk field of 2 - 20 uG in a lensing galaxy at z=0.685 (6.3 Gyr ago), in agreement with the magnetic field strength and structure of nearby galaxies. Then, I will show how the observables of magnetic fields evolve over redshift using 16 500 galaxies at redshifts of 0 < z < 2 from the state-of-the-art cosmological magneto-hydrodynamic simulation IllustrisTNG50. I explore two methods used to obtain cosmic magnetic field strengths: deriving the magnetic field strength of intervening galaxies in front of polarized background quasars and deriving the magnetic field strength of the IGM by utilizing FRBs. In the near future, we expect the number of known lensing systems, quasars with intervening galaxies, and polarized FRBs to dramatically increase by tens of thousands of systems due to new radio surveys and telescopes. The results I am presenting demonstrate how the lensing method can be applied to different galaxies, and predict measuring the magnetic field strength of the IGM with a 2 rad m^-2 precision using FRBs will be possible in under 10 years.

	Main Colloquium
Prof. Dr. Julia Tjus	ORATED

RUB

Active galactic nuclei have long been discussed to be the sources of ultra-high-energy cosmic rays. The reason is simple: they are among the very few source classes that provide the right parameter range in terms of magnetic field strength and size that fulfill the necessary criterion for the acceleration to the highest observed cosmic-ray energy of 1e20eV. To prove this statement, or even to narrow down if the acceleration region sits in the inner jet, the termination show of the jet or the core is one of the major challenges in astro- and astroparticle physics. As cosmic-rays do not travel in straight lines, their directional information does not help for an anumbiguous identification. Iin this talk, it will be discussed how knowledge about the magnetic field structure and strength help to identify the origin of the acceleration zone and how we can use neutrinos to further pinpoint how active galaxies contribute to the cosmic ray spectrum.

	Informal Colloquium
Dr. Leonid Petrov	ORATED

NASA Goddard Space Flight Center, USA

Processing the output of assimilation numerical weather models, one can derive the state of the atmosphere on a 4D grid. When we know the state of the atmosphere, we can compute path delay in the neutral atmosphere, atmospheric opacity, and brightness temperature of the atmosphere to a given station, given azimuth and elevation, and given moment of time. NASA Goddard Space Flight Center runs a suite of operational assimilation numerical weather model. In addition, NASA runs an operational service for computation of slant path delays, atmospheric opacities, and brightness temperatures. An overview of these data products will be given, and their use in data analysis will be discussed.

	Special Colloquium
Dr Minghui Xu	ORATED

GFZ Potsdam

Effect of source structure is the (only) dominant factor that limits the accuracy of the celestial reference frame. The AGNs in absolute astrometric and geodetic observations are still assumed to be an ideally point on the sky although their structure and its evolution over both time and frequency are well understood in radio astronomy. I will report on my study about investigating these effects based on the observations from the new generation geodetic VLBI system, VLBI Global Observing System (VGOS). VGOS makes regular observations since 2019 with a network of 7 to 12 antennas simultaneously at the four bands in the range of 3 to 11 GHz. This network is expanding globally. I have imaged these VGOS observations on a routine basis via closure images because of the known issue of missing antenna calibrations for geodetic antennas. These VGOS images show that nearly all VGOS sources have “invisible” structure at the angular scales of 0.1 milli-arcsecond or higher. Another challenge of modeling source structure in VGOS observations is the image alignment over the four frequencies, where core shift will also play a role. According to my simulations, any misalignment among the highest three frequency bands is magnified in the source position estimates from VGOS. I will report on how to valid the image alignment by using phase delays. It is to be noted that not only for geodesy but also for astrometry modeling source structure is so important and is the necessary step forward.

	Special Colloquium
Lennart Heino	ORATED

University of Cape Town

This study explores the polarised emission of the faint extragalactic radio sources in the MIGHTEE (MeerKAT International Giga-Hertz Tiered Extragalactic Exploration, Jarvis et al., 2016) survey in order to systematically study cosmic magnetic fields in galaxies to high redshift. Tracing he presence and contribution of magnetic fields is an important aspect of understanding galaxy evolution. Reaching a sensitivity of 2 muJy/beam at a resolution of 6 arcseconds, MIGHTEE is providing an opportunity to chart the evolution of polarised emission from distant galaxies over cosmic time. The MIGHTEE survey detects polarised emission for a large number of radio sources down to total intensity flux densities of the order of 100 muJy. At these flux densities the source population is increasingly dominated by star-forming galaxies (SFGs) as opposed to active galactic nuclei (AGNs) which are dominant at high flux densities. Observations of the local universe show that both, AGN and SFG phenomena, are permeated by magnetic fields. Polarised emission of AGN can be traced to very distant galaxies. However, polarised emission of SFGs at moderate distance has been detected only once. I use multi-wavelength criteria to classify MIGHTEE radio objects as either SFG or AGN. I perform Rotation Measure Synthesis (RMSY) on the spectro-polarimetric data cubes and use the polarisation and RMSY spectra to search for polarised emission. A comparative analysis of the polarisation properties of SFGs and AGNs is performed. The analysis is extended to the lowest possible flux densities using stacking techniques. I will show results of the MeerKAT polarisation studies of radio sources down to a sensitivity at the micro-Jansky level.

	Special Colloquium
Dr. Nuria Jordana	ORATED

RUB

Gamma-ray bursts (GRBs) are bright extragalactic flashes of gamma-ray radiation and the most energetic explosions in the Universe. Their catastrophic origin —the merger of compact objects or the collapse of massive stars— drives the formation of a newborn compact remnant (black hole or magnetar) that powers two highly relativistic jets. As these jets continue to travel outwards, they collide with the external material surrounding the dying star, producing a long-lasting afterglow that can be seen across the entire electromagnetic spectrum, from the most energetic gamma-ray emission to radio wavelengths. But how can such material be accelerated and focused into narrow beams? To distinguish between jet models and ultimately determine the power source of GRBs, we study the polarization of the light during the first minutes after the explosion (using novel instruments on fully autonomous telescopes around the globe) and we directly probe the magnetic field properties in these extragalactic jets. In this talk, I will review the recent developments that have been made using this technology. Those include some insights on the progenitors and remnants of these energetic explosions, the first detection of highly polarized optical light from a GRB and confirmation of mildly magnetized jets, and the case of an exceptionally high-energy GRB produced by a highly magnetized jet.

	Main Colloquium
Dr. Elena Redaelli	ORATED

MPE

Research into star formation is a highly active area of modern astrophysics. Stars are born in dense and cold environments known as molecular clouds, which appear as dark patches in the night sky as optical radiation cannot penetrate them. Since these clouds are composed of molecules, molecular transitions at radio and microwave wavelengths represent the ideal diagnostic tool to probe these phases of the interstellar medium. I will show how through their analysis we can infer the physical and chemical structure of star-forming regions, to understand how they evolve. I will showcase examples of the power of this technique in both the low- and the high-mass regimes, each with its set of challenges.

	Special Colloquium
Dr. Leonid Gurvits	ORATED

JIVE and TU Delft

In this impromptu presentation I will cover two VLBI topics pursued merely 240 km NW of Bonn. The first one deals with the initiative to build a next generation spaceborne VLBI system. I will start from a brief (and known to many in the audience) concept called TeraHertz Exploration and Zooming-in for Astrophysics (THEZA) as it stands now, five years after proposing it to ESA. I will then review a (much) scaled down version of THEZA called Black Hole Explorer (BHEX), also known to some people in the audience. BHEX is aiming to address a truly transformative science of the phenomenon of photon rings surrounding black holes. BHEX is led by a joint team of two major US establishments, Harvard CfA and NASA Goddard Space Flight Center, supported by other US research organisations, but has representatives from Europe and Japan too. Both initiatives, THEZA and BHEX can be seen as spaceborne extensions of global VLBI, EVN, VLBA, GMVA, EHT, ngEHT, ngVLA, etc. (cross out what you find irrelevant). My main take-home message from this part of the presentation is simple: spaceborne VLBI is inevitable. We better start thinking and working on this before too long. In the second part of this presentation, I will show results of the ongoing study of two newly suspected systems containing supermassive black hole binaries (SMBHBs). According to all reasonable scenarios of astrophysical evolution of galactic systems SMBHBs must exist and be abundant. They are expected to be major contributors to the gravitation wave background in the range of frequencies 0.1 mHz – 1 Hz which is to be covered by the Laser Interferometer Space Antenna (LISA) once it is up and running in the 2030s. Yet, as a class, SMBHBs remain rather elusive. There are several famous and rather likely suspects (e.g., OJ 287 – an object very well known in this audience, and several others). There is a number of much less known and sure cases, like those several I will present here. However, the overall statistics of more or less known suspected cases of SMBHB looks quite problematic from many astrophysical and cosmological standpoints. I will present our view on possible evolution of two new SMBHB suspects and present estimates of their inspiralling toward final coalescence accompanied by a gravitational wave outburst. Such outbursts are being assumed as potentially valuable cosmological probes called “standard sirens”. They will join the club of other standard objects (rods, candles), and together they will mark the birth of multimessenger observational cosmology.

	Master Colloquium
Mr. Abhinav Tyagi	ORATED

AIfA

The discovery and analysis of binary pulsars in compact orbits offer unique opportunities to test theories of gravity, particularly General Relativity, in the strong-field limit. Modern pulsar searches, often conducted in quasi-real-time using large GPU-based HPC clusters, underscore the critical need for speed in processing and analyzing this data. In this talk, I will introduce PulsarNet, a machine learning (ML) pipeline designed for the detection and parameter estimation of binary pulsars in time-series observations. PulsarNet (PN) represents the first fully ML-based search pipeline of its kind, marking a significant departure from conventional matched filtering techniques. It achieves comparable sensitivity for sinusoidal signals and pulsars with a high duty cycle (>15) and offers substantially faster processing speeds than traditional searches. PN employs a two-part ML model: comprising a classifier that pinpoints plausible pulsar signals in the Fourier domain, along with an innovative 'Attention'-based parameter predictor network for estimating the period and period derivative of a signal used to fold the data. While our early results are encouraging, I will also address some challenges of using a complete ML-based approach for pulsar searches, including recovering sensitivity for pulsars with a high number of harmonics in the Fourier domain. After training purely on simulated white noise data, we applied PN to search for pulsars in the Terzan 5 globular cluster and were able to recover 80% of the pulsars compared to traditional searches, while being 13 times faster. We anticipate that future models can bridge this sensitivity gap by implementing harmonic summing and retraining on real observations. PN stands as a proof-of-concept that purely ML-based searches are not only feasible but with some additional work can be effective for future pulsar processing, opening up a new parameter space for astrophysical discoveries.

	Special Colloquium
Dr. Christophe Risacher	ORATED

IRAM

I will present the current IRAM instrumentation at our two observatories (NOEMA and the 30m telescope) before detailing the current ongoing upgrade for NOEMA, preparing a dual-band observing mode capability (observing the 3 mm and 1.3 mm in parallel), which does require doubling the IF processing / transport and backends to allow using the full available instantaneous bandwidth. We will also show some of our development projects for the future generation receivers, aiming at increasing the IF bandwidth of the heterodyne receivers, to 4-20 GHz IF BW. Finally, we will show the plans and progress of our developments of large multibeam receivers for 3 mm and 1.3 mm for the IRAM 30m telescope.

	Main Colloquium
Prof. Dr. Tessa Baker	ORATED

University of Portsmouth

The first eight years of direct gravitational wave detection have had a huge impact not only on astrophysics, but also on cosmology and fundamental physics. Central to these developments have been Sirens, gravitational wave sources for which we can measure both distances and redshifts. The most spectacular kind of sirens are multimessenger events like the binary neutron star merger GW170817, with both gravitational wave and electromagnetic counterparts. However, these represent only a tiny fraction of all gravitational wave events. So are all the other gravitational wave events useless, from a cosmology perspective? In this talk I'll introduce the alternative Dark Sirens method, which enables us to extract cosmology from regular, non-counterpart gravitational wave events. I'll explain how this technique can be used to obtain an independent measurement of the Hubble constant, and also to test the laws of gravity operating on the largest scales. I'll describe some subtleties that require careful handling, (hopefully!) convince you that we can overcome them, and show the latest results obtained from gravitational wave detections to date.

	Special Colloquium
Dr. Nienke van der Marel	ORATED

Leiden University

Structures such as gaps and rings in ALMA observations of protoplanetary disks have long been hailed as signposts of planet formation. However, a direct link between exoplanets and protoplanetary disks remained hard to identify. Recent work has shown that gapped disks retain high millimeter-dust masses up to at least 10 Myr, whereas the majority of disks is compact and decreases its dust mass rapidly. This can be understood when considering dust evolution, where dust traps prevent radial drift in the gapped disks. The fraction of gapped disks shows a stellar mass dependence, and I propose a scenario linking this dependence with that of giant exoplanet occurrence rates. It is shown that there are enough exoplanets to account for the observed disk structures if gapped disks are caused by exoplanets more massive than Neptune, under the assumption that most of those planets eventually migrate inwards. On the other hand, the known anti-correlation between transiting super-Earths and stellar mass implies those planets must form in the compact disks, consistent with those exoplanets forming through pebble accretion in drift-dominated disks. I will demonstrate some of the latest insights on rocky planet formation in compact disks, as well as new insights on gas giant planet formation in larger gapped disks. Finally, I will show that dust traps and radial drift may play a crucial role in regulating the chemical composition of disks, which sets the C/O ratio of exoplanet atmospheres as traced in the coming years with the James Webb Space Telescope.

	Special Colloquium
Dr. Sasha Plavin	ORATED

Black Hole Initiative, Harvard University

Increasing numbers of high-energy neutrinos coming from blazars are being detected, but data sparsity makes it challenging to quantitatively describe each source individually. In this talk, we present the results of modeling the distribution of a bright blazars sample, taking their geometry and observed radio and neutrino properties into account. This lets us constrain the contribution of all blazars to high-energy neutrino flux, to evaluate the effects of relativistic beaming, and to estimate hadrons contribution to the total jet power.

	Main Colloquium
Dr Julia Stadler	ORATED

MPA

A new generation of galaxy surveys is soon to release their first data. While holding the potential to transform our understanding of the origin and evolution of the Universe, the analysis of these datasets poses considerable challenges. The state-of-the-art approach compares theory and data in terms of summary statistics, such as the galaxy power spectrum. However, information is lost in this compression. Another major concern is theoretical uncertainties in the small-scale processes of galaxy formation and consequently in the galaxy bias relation. Forward modeling the three-dimensional large-scale galaxy density enables the comparison between model and data at the level of density fields, and thereby it foregoes the loss of information in the data compression step. By basing the forward model on perturbative methods, namely the Effective Field Theory of Large Scale Structure (EFT of LSS), one can robustly marginalize over theoretical uncertainties in the galaxy bias relation. Such an analysis not only provides tight cosmological parameter constraints but also offers insights into the initial conditions and structure formation history over the survey volume. I will discuss the status of field-level analysis for galaxy clustering and show results and developments with the LEFTfield code. Forward modeling allows for the self-consistent incorporation of many observational effects, and I discuss redshift-space distortions as an important step on the way to realizing the potential of this technique for observational data.

	Special Colloquium
Dr. Etienne Bonnassieux	ORATED

University of Wuerzburg

In the last few years, the international LOFAR baselines have become accessible to a broad public at 144 MHz. This is due to a better understanding of the instrument itself, the development of new techniques, and the availability of a dedicated pipeline. In this talk, I will give a brief introduction to the general problem of interferometry, the specific case of VLBI, and the hybrid case of LOFAR-VLBI, with an eye on future SKA-VLBI and ngVLA. I will then give specific examples, and conclude with concrete scientific returns made possible with the investment of time and energy in technical interferometric work.

	Special Colloquium
Prof. Dr. Peter L. Biermann	ORATED

MPI für Radioastronomie

The WAT (wide angle tail) radio galaxies ESO 137-006 and 3C338 show radio filaments including some extending between the two radio tails. If, in analogy to the Parker Solar wind, jets carry a powerful relativistic electric current, driven by gradient drift currents of particles in a $p^{-2}$ spectrum, Maxwell's continuity equation shows that a temporal variation in jet power would inevitably lead to a localized short-lived charging-up, i.e. a temporary patch of electric field. Progenitors of the observed radio filaments are the relic jets left by repeated episodes of nuclear activity and pushed sideways by the ram pressure, though remaining connected to the broad radio lobes. The Debye shielding distance using the same $p^{-2}$ spectrum approaches the radio galaxy scale, with a huge total energy content. Here we propose that discharges dissipating the transient patches of electric fields through the filaments illuminate them. The same process will illuminate jets emanating from rapidly rotating young stellar mass black holes (BHs), and lead to lightning. Lightning allows particle spectra of $p^{-3}$ to $p^{-5}$ for electrons, as visible in radio data of Galactic filaments, and extragalactic filaments; correspondingly protons and other nuclei have spectra of $p^{-2}$ to $p^{-4}$. The steep spectrum allows a steep dependence of residence time on energy/momentum with $p^{-5/3}$, that is suggested by fits to the AMS spectra for transport in the OB-Super-bubble: Based on earlier ideas here a model is proposed that focusses on the cosmic ray interaction first in the wind shock shell of super giant stars, when the supernova driven shock races through, and second in the OB-Superbubble full of lightning: The two key aspects are i) a much larger column of interaction, allowed because of heavy element enrichment of the interaction zone, and ii) even He, C, and O may have a small secondary contribution, as the difference to the Fe spectrum suggests; this small secondary component is visible in the $^3$He data. In this model OB-Superbubbles are thunderstorms.

	Master Colloquium
Sachin Pradeep	ORATED

MPIfR

Fast Radio Bursts are subject to scattering and scintillation due to interactions with one or more plasma screens within the interstellar medium or the halos of the host galaxy and the Milky Way. These screens contain structures of AU scales, which lead to the multipath propagation of the single pulses. A common argument is that when two screens appear "pointlike" to each other, they scintillate on the scale of both screens. This condition is commonly invoked to constrain scattering to FRB host galaxies. In this study, we use simulations to explore the resolving phase space where the screens appear extended to each other and its effect on observables. The main result is the quenching of broad-scale Milky Way scintillations when the screens resolve each other. Additionally, we demonstrate through simulations that the quenching phenomenon can be used to locate the host galaxy screen, thereby probing the host galaxy ISM at AU scales. The work also introduces a new theoretical model and a novel simulation tool to study multi-screen scattering, which can be easily adapted to study images arising from gravitational lensing and microlensing from CGM clouds.

	Main Colloquium
Prof. Dr. Tom Ray	ORATED

Dublin Institute for Advanced Studies

+++ Note the unusual time to accommodate the speaker +++ One of the primary goals of the James Webb Space Telescope (JWST) is to investigate the very earliest stages of star formation. This is a task well suited to JWST as it is capable of observing through dust-enshrouded molecular clouds with unprecedented spatial resolution and sensitivity. After reviewing JWST’s capabilities, I will explore what we have learned in the first 18 months of operation about the outflows that the youngest stars launch, the chemistry of their associated accretion disks, and the relationship between the two.

	Main Colloquium
Dr. Alexandra Veledina	ORATED

Turku University

Imaging X-ray Polarimetry Explorer (IXPE) is the first satellite fully dedicated to X-ray polarimetry measurements. It is sensitive to the direction of the electric field in the X-ray photons and examines the polarization of the incoming signal - the excess of photons with a given direction of electromagnetic wave oscillations. Polarization arises from the broken spherical symmetry of the system and is a fine tool to probe the source geometry. IXPE operations have revealed pivotal insights into various astrophysical phenomena, including accreting black holes and neutron stars, pulsars and their nebulae, magnetars, blazars, and the center of our Galaxy. In this presentation, I will give an overview of the novel findings in the field of accreting black holes, as illuminated by IXPE data.

	Special Colloquium
Dr. Nicola Marchili	ORATED

Istituto di Radioastronomia - INAF, Bologna, Italy

Compact radio sources can show remarkable flux density variations at GHz frequencies on a wide range of timescales. The origin of the variability is a mix of source-intrinsic mechanisms and propagation effects, the latter being generally identified with scattering from the interstellar medium. Some of the most extreme episodes of variability, however, show characteristics that are not consistent with any of the explanations commonly proposed. I will present the results of an in-depth variability analysis carried out on light curves from the impressive database of the US Navy's extragalactic source monitoring program at the Green Bank Interferometer (GBI), a long-term project mainly aimed at the investigation of extreme scattering events. I will show that the Sun heavily contributes to the variability observed in compact radio sources.

	Special Colloquium
Dr. Jakob Knollmueller	ORATED

TU Munich

Sagittarius A* (Sgr A*), the supermassive black hole at the heart of our galaxy, provides unique opportunities to study black hole accretion, jet formation, and gravitational physics. The rapid structural changes in Sgr A*’s emission pose a significant challenge for traditional imaging techniques. We present dynamic reconstructions of Sgr A* using Event Horizon Telescope (EHT) data from April 6th and 7th, 2017, analyzed with a one-minute temporal resolution with the resolve framework. This Bayesian approach employs adaptive Gaussian Processes and Variational Inference for data-driven self-regularization. Our results not only fully confirm the initial findings by the EHT Collaboration for a time-averaged source but also reveal intricate details about the temporal dynamics within the black hole environment. We find an intriguing dynamic feature on April 6th that propagates in a clock-wise direction.

	Main Colloquium
Dr. Sara Ellison	ORATED

University of Victoria

Astronomy's current model of galaxy evolution is built on a foundation of hierarchical growth, in which small galaxies merge together to form larger ones. In addition to the simple accrual of mass, this merging process is predicted to fundamentally change the galaxies properties, such as dramatic morphological transformations, the triggering of bursts of star formation and high rates of accretion onto the central supermassive black hole. In this talk I will explain the physical processes behind these predictions, and present the observations that we are performing in order to test the theory. Although many of the predictions are indeed borne out by experiment, there have been some surprising conflicts as well, that demand revisions to our models of how mergers shape galaxy evolution. +++ Note the unusual time & that this is an online-only colloquium +++

	Special Colloquium
Dr. Etienne Bonnassieux	CANCELED

University of Wuerzburg

TBD

	Main Colloquium
Dr. Enrique Lopez-Rodriguez	ORATED

Stanford University

Galaxy evolution strongly depends on the physics of the interstellar medium (ISM). The ISM is permeated by B-fields, in which magnetic energy is in close equipartition with the thermal energy. This physical condition makes the B-fields dynamically important at several stages of galaxy evolution affecting gas flows in the ISM and driving gas inwards toward the galaxy's centers, and outwards toward the intergalactic medium via galactic outflows. Thus, B-fields remain an important, but still highly ignored, ingredient to understanding the evolution of galaxies across cosmic time. Far-infrared and sub-mm wavelengths have recently been key to providing a complete picture of extragalactic magnetism by doing what only HAWC+/SOFIA, JCMT/POL-2, and ALMA can do: measuring magnetic fields in the densest areas of the universe. Using FIR/Sub-mm and radio polarimetric observations, in combination with the kinematics of the neutral and molecular gas, a topographic study of B-field in galaxies is characterized for the first time. In this talk, I will present the results of SALSA (Survey for extragALactic magnetiSm with SOFIA Legacy Program): the magnetic properties in the multi-phase ISM of nearby galaxies observed in the wavelength range of 50-890 um. These results have opened a new window of exploration on galaxy evolution and provide the building blocks for scientific cases of future IR polarimetric missions. +++ The speaker will be staying at the institute from 29.01 to 02.02+++

	Special Colloquium
Sang-Hyun Kim	ORATED

Korea Astronomy and Space Science Institute and the University of Science and Technology, Korea

Blazars are a subclass of active galactic nuclei (AGNs) and are among the most powerful objects in the universe. Their relativistic jets are pointing towards Earth, resulting in relativistically boosted emission, rapid variability, and superluminal jet motions. The variable emissions extending from radio to gamma-ray energies indicate that blazar jets are efficient and energetic particle accelerators. However, despite many discoveries and detailed studies, there are still some long-standing puzzles of blazar jet physics that remain unsolved. For instance, what are the particle contents of jets? What physical mechanisms drive the particle acceleration in jets? Where and how do jets generate high-energy emissions? This study aims to address these questions by exploring the multiwavelength light curves of a blazar CTA 102. This source exhibits flaring activity from radio to gamma-rays in 2012–2018 observations. Very long baseline interferometry (VLBI) observations of the source show a compact bright region at the upper end of the parsec-scale jet referred to as the VLBI core. Strong correlations between the core flux variability and the single-dish flux variability suggest that the variability of radio emissions may come from the very compact core region. In this talk, I will present the results from this work, including spectral properties and magnetic field strengths of the synchrotron self-absorption region, multiwavelength correlations with respect to the gamma-ray light curve, and VLBI kinematics of the radio jet related to gamma-ray flares. I will also introduce a study on the association of a blazar PKS 0735+178 with high-energy neutrinos, in collaboration with the TeV Effelsberg Long-term AGN Monitoring (TELAMON) program.

	Main Colloquium
Dr. Elena Redaelli	CANCELED

MPE

Research into star formation is a highly active area of modern astrophysics. Stars are born in dense and cold environments known as molecular clouds, which appear as dark patches in the night sky as optical radiation cannot penetrate them. Since these clouds are composed of molecules, molecular transitions at radio and microwave wavelengths represent the ideal diagnostic tool to probe these phases of the interstellar medium. I will show how through their analysis we can infer the physical and chemical structure of star-forming regions, to understand how they evolve. I will showcase examples of the power of this technique in both the low- and the high-mass regimes, each with its set of challenges.

	Special Colloquium
Dr. Juliusz Doboszewski	ORATED

University of Bonn

Assessment of scientific theories is an important part of modern science. But how to go about it in the (rather unique) epistemic situation we find ourselves in cosmology? After all, we only have access to a limited portion of a single universe. In this context, attention to conceptual and philosophical issues can be particularly useful for cosmologists. I will introduce some philosophical notions, including elements of confirmation theory, approaches to eliminative reasoning, non-empirical theory assessment, and problems of underdetermination and unconceived alternatives. For illustration I will discuss three episodes: 1950s debates about steady state theory, 2010s debates about inflation, and the current search for primordial black holes. About the speaker: Juliusz is postdoctoral researcher in the Lichtenberg Group for History and Philosophy of Physics at Uni Bonn, also affiliated with the Harvard University's Black Hole Initiative and involved in the next generation Event Horizon Telescope. He focuses on philosophy of astrophysics, especially global spacetime structure in general relativity and QFT in curved spacetime & quantum gravity.

	Promotionskolloquium
Jompoj Wongphecauxson	ORATED

MPIfR

Pulsars are rotating neutron stars that emit pulsating signals. They serve as valuable tools for studying a wide range of topics, from general relativity to the interstellar medium. The discovery of a pulsar in the Galactic centre (GC) would be particularly fascinating due to its proximity to the Sgr A\*, the black hole at the centre of our Galaxy. Such a discovery could provide insights into the local environment and the nature of the black hole itself. In the GC, up to 1000 pulsars were predicted, but thus far only six have been found, including a magnetar. One of the explanations is that the dense environment in the GC causes extreme interstellar scattering, reducing the sensitivity of pulsar surveys, particularly for short-period pulsars. To improve our sensitivity to long-period pulsars, a Fast Folding Algorithm (FFA) was used rather than the traditional Fast Fourier Transform (FFT). During my study, an FFA pipeline for accelerated pulsars was implemented for the first time to search for pulsars within 1 deg around GC using the data from the High Time Resolution Universe Pulsar Survey-South Low latitude. In this work, a new slow pulsar (PSR J1746-2829) was discovered with an angular distance of ~0.5 deg from the GC. Follow-up observations revealed that this pulsar has properties that are usually associated with radio magnetars. Interestingly, there is another object in the GC that shows magnetar-like properties, in addition to the known magnetar. This may suggest that the GC has an anomalously large fraction of magnetars to non-recycled pulsars compared to the rest of the Galaxy. Extreme interstellar scattering can significantly reduce the sensitivity of pulsar surveys. Fortunately, the scattering time is decreasing with the fourth power of the observing frequency. As a result, the FFA pipeline for accelerated pulsars was modified to search for a high observational frequency (230 GHz) dataset from the three most sensitive stations from the Event Horizon Telescope observations of Sgr A* in 2017. This survey is the highest frequency pulsar survey to date, leading to negligible interstellar effects. However, pulsars have a steep spectrum, making them dimmer at higher frequencies, and harder to detect. We used the FFA and FFT with acceleration search pipelines to search for pulsars in this dataset, but no new pulsars were detected. The further empirical sensitivity analysis shows that we are only sensitive to less than 2\% of the known pulsar population in this search, with less sensitivity on the slow pulsars, highlighting the need for FFA searches.