Promotionskolloquium
Saurabh	ORATED

Max Planck Institute for Radio Astronomy

The 230 GHz Event Horizon Telescope (EHT) observations of M87* revealed a polarized ring with a central brightness depression, and 86 GHz Global Millimetre VLBI Array observations resolved the ring and the extended jet. The 2021 EHT campaign, adding NOEMA and the Kitt Peak 12 m telescope, supplied the intermediate baselines connecting these scales. We analyzed the 2021 M87* dataset and using closure phases, we recovered a Gaussian component offset by about 5500 AU with flux density of about 60 mJy (an upper limit), the first 230 GHz detection of the jet base, with most of the previously missing emission arising on larger scales. We employed a semi-analytic radiatively inefficient accretion flow (RIAF) model to analyze the 2017 EHT polarimetric data. This showed that disk thickness has little effect on the observables, toroidal and poloidal fields are distinguishable, and the polarization favors a partially infalling sub-Keplerian flow. GR also admits horizonless collapse end states under physically reasonable matter conditions, and horizon-scale precision now makes this assumption testable. We adopt the Joshi-Malafarina-Narayan 1 (JMN-1) spacetime, an exact horizonless solution from anisotropic collapse and the best available black hole mimicker, to RIAF imaging and to the first three-dimensional GRMHD simulation of sustained accretion onto such an object. JMN-1 produces images nearly indistinguishable from a black hole at current resolution, predicting a smaller inner shadow as a key discriminant for the upcoming/future VLBI missions such as ngEHT and BHEX.

	Main Colloquium
Dr. T. Joseph W. Lazio	ORATED

University of Michigan

SunRISE is a constellation of six identical small spacecraft (6U CubeSats) that will form a space-based VLBI array. Each spacecraft carries a decametric-hectometric (DH, 0.1 MHz to 25 MHz) receiving system paired with global navigation satellite system (GNSS) receivers. The Solar DH receivers will be used to record signals from Type II and Type III solar radio bursts while the GNSS receivers will time stamp the data and enable the determination of the spacecraft locations for subsequent ground-based cross-correlation. SunRISE will reveal aspects of how solar energetic particles (SEPs) are accelerated at coronal mass ejections (CMEs) by tracking Type II bursts and how SEPs are released into interplanetary space from the Type III bursts. The six spacecraft that form the SunRISE interferometer will fly in a passive formation in a supersynchronous geosynchronous Earth orbit (super-GEO). The nominal baseline will be 10 km, obtaining an angular resolution of approximately 10' at 10 MHz. I describe the implementation of SunRISE, illustrating how the combination of on-board and ground operations and processing are required to achieve a fully space-based VLBI array. While SunRISE is a NASA Mission of Opportunity that will conduct science in its own right, it also is intended to be a pathfinder for future space-based radio astronomy missions. I provide an initial assessment of the "experience gained" for future missions, from the perspective of both the SunRISE science and technical implementation.

	Special Colloquium
Dr. Xavier Rodrigues	ORATED

Astroparticle and Cosmology Laboratory, Université Paris Cité

Over the past decade, the IceCube South Pole observatory has produced indications of high-energy neutrinos in association with blazars, suggesting that AGN jets may be powerful hadronic colliders, as expected theoretically. However, neutrino data face limited statistics and large uncertainties on key observables, such as the true energy of the neutrinos. From the theory side, the widely used one-zone blazar model faces critical degeneracies and fails to capture the radio emission from the extended jet, preventing a holistic interpretation of the multi-messenger data. In this talk, I discuss recent efforts to go beyond the one-zone blazar paradigm. By considering the jet's extension from the base down to the parsec scale using robust jet kinematics, we can jointly describe neutrino and multi-wavelength emission down to radio frequencies that cannot be constrained by the single-zone approach. By shifting from purely phenomenological parameterizations to a physics-driven description of particle acceleration and diffusion along the jet, we can make concrete statements on the expected neutrino energies, the time-domain multi-wavelength emission, and the viability of each source as a neutrino emitter, transforming the role of source modeling from descriptive to predictive.

	Special Colloquium
Niloofar Pourjafari	ORATED

University of Calgary

Magnetic fields are an important component of the interstellar medium, influencing the transport of cosmic rays and the interaction between galactic disks and halos. NGC 891, one of the closest Milky Way analogues, provides an excellent opportunity to study these processes in an edge-on system. In this talk, I will present new VLA S-band polarization observations of NGC 891 combined with existing C-band data from the CHANG-ES survey. We detect a large-scale polarized halo and find evidence for an ordered magnetic field extending across the galaxy. The observations suggest that much of the observed polarized emission originates on the near side of the galaxy, providing a new perspective on the magnetized halo of this highly inclined system. We also identify localized polarized structures on kiloparsec scales in the north-eastern halo that coincide with diffuse X-ray and Hα emission. These features likely trace magnetic fields associated with recent star formation activity and feedback, possibly including a superbubble powered by clustered supernovae. Together, these observations reveal both the global magnetic field structure of NGC 891 and the influence of local star formation activity on its halo.

	Main Colloquium
Prof. John McKean	ORATED

Kapteyn Astronomical Institute, University of Groningen & ASTRON, Dwingeloo, The Netherlands

Gravitational lensing provides a powerful probe of the global mass properties of galaxies, which are best tested using observations at extremely high angular resolution. In addition, through detailed observations of the lensed images, it is possible to place tight constraints on the nature of dark matter through measuring the abundance and properties of low mass haloes via their subtle gravitational lensing signal. Here, we first present new observations with the VLA and HSA to better understand the source of so-called flux-ratio anomalies in four image gravitational lenses, which historically provided the first constraints on CDM using lensing studies. Next, we will present the analysis of the mass properties of ten massive elliptical galaxies at intermediate redshifts, by combining gravitational lensing and the sensitivity and resolving power of the Atacama Large Millimetre Array (ALMA) and global Very Long Baseline Interferometry (radio VLBI). Using imaging at 25 to a few milli-arcsecond resolution, we find that complex mass models with angular structure are strongly favoured by the data. In addition, such observations are sensitive to small-scale structure either in the lens or along the line-of-sight to the background source. From such an analysis of the data from global VLBI observations, we detect of a low mass (million solar mass) dark object, whose properties are inconsistent with a dark matter halo from either cold or warm dark matter models, but may be in agreement with more exotic models, like self-interacting dark matter. Finally, we present a brief overview of future studies using the SKA and a likely African VLBI facility that includes the SKAMPI, MPG-DZA and AMT dishes. Throughout we will also provide some asides on the pc-scale structure of radio jets, constraints on galactic-scale magnetic fields and electron densities, and the super-resolved (about 10 to 20 pc-scale) properties of starburst galaxies at redshifts 1 to 4.

	Main Colloquium
Professor Ziggy Pleunis	ORATED

University of Amsterdam

Fast radio bursts (FRBs) are one of the most exciting mysteries in contemporary astrophysics. They last only a fraction of a second but are bright enough to be detectable from halfway across the Universe. FRBs are unique astrophysical tools: they are perfect point sources, impulsive, and being in the radio band they are also distorted in ways that carry valuable information about otherwise invisible matter, which makes them unprecedented probes of the local environments of compact objects and the structure and magnetization of the interstellar and intergalactic media. FRBs will be even more useful when we better understand their sources and emission. A small fraction of FRBs has been observed to repeat, which has ruled out a cataclysmic origin for these sources and allows for detailed multi-wavelength follow-up observations that constrain FRB models. It is as-yet unclear whether all FRBs repeat and if FRB models based on a few well-studied repeaters can be extrapolated to the full population. Canada's CHIME telescope has been instrumental in uncovering the diversity of FRBs: it provided the first large statistical sample of FRBs, and it is continuing to lead the discovery of repeating sources by revisiting the Northern sky every day. At the same time, we have opened a new window into studying these sources by detecting the lowest-frequency FRBs with the LOFAR telescope. I will argue that the next revolution in FRB science is imminent through the collection of the first large sample of FRBs with known redshifts through the CHIME/FRB "Outriggers" upgrade. Complemented by observations from LOFAR 2.0 and other facilities, this promises to solve the mystery of FRBs and will uniquely address a variety of unsolved problems in astrophysics, such as the detection of the "missing" baryons and the impact of feedback on the formation of galaxy haloes.

	Special Colloquium
Prof. Shrinivas Kulkarni	ORATED

California Institute of Technology, Pasadena, USA

What unites the following: high velocity clouds crashing into the Galactic disk, wide and/or ultra-deep narrow band imaging by amateur astrographers, state-of-the-art IFUs with considerable grasp (MUSE, Keck Cosmic Imager, the Local Volume Mapper), bow shocks of various types, zombie nebulae and ionized cometary nebulae. The common factor is sizzling discoveries. Attend this seminar to learn more! Please note: Coffee and Tea at 15:45

	Special Colloquium
Dr. Christian Fendt	ORATED

MPIA Heidelberg

I will show resent results of connecting relativistic MHD simulations of pc-scale AGN jets to mock emission maps applying a subgrid model of diffusive shock acceleration of highly relativistic particle and subsequent synchrotron cooling. Due to the full 3D data cube and full time resolution we can derive emission maps for different viewing angles, as well as variability studies for the jet spectrum and jet variability. We can further follow the motion of radiation patterns, and find that these follow the shock motion rather than the jet fluid velocity. These jet knots thus identify different shock structures in the jet, also indicating different particle populations, each defined by the age and motion of the respective shocks.

	Special Colloquium
Dr. Frederic Jaron	ORATED

TU Vienna

The geodetic and astrometric application of VLBI is a powerful technique for the realization of global reference frames and the measurement of Earth orientation parameters. Source structure is one of the remaining unmodeled errors that prevent the technique from reaching its ultimate accuracy goals. We have developed a method to remove the influence of source structure from the output of the DiFX software correlator that fits into the common geodetic processing pipeline. In this talk I will present our approach and its application to observational data of the VLBI Global Observing System (VGOS). Improvement of closure group delays and post-fit residuals is obtained for selected sources when reliable image information is available.

	Special Colloquium
Prof. Tom Megeath	ORATED

University of Toledo, Ohio

I will present a study of jets and winds from protostars across the mass spectrum with JWST. These data show collimated jets and wide angle winds from five protostars with masses from 0.12 to 12 solar masses. I will describe our efforts to disentangle the jets from the massive protostar I20126 from those of its companions, and the detection of the jet from the massive protostar in ionic species. I will then overview current results from the HEFE, a 190 hour large program on JWST. Here we show star formation in the filamentary OMC2/3 region of Orion, likely the most active region of ongoing star formation in the nearest 500 pc. Using NIRCam multiband imaging of the entire region and IFU imaging of 13 Class 0 protostars, these provide a detailed picture of feedback from outflows in this filamentary environment. I will focus on HOPS 383, a protostar that recently underwent a 15 year outburst, and our efforts to find a counterpart to the outburst in the jet from this protostar.

	Main Colloquium
Dr. Jaroslav Haas	ORATED

Charles University, Prague

The centre of our Galaxy hosts a supermassive black hole called Sgr A*. Its nature has been tested in various ways and is now considered proven beyond any reasonable doubt. The properties of the population of the less massive black holes in this region are, however, far less certain. In my talk, I will present a specific way to probe the distribution of the generally expected stellar-mass black holes in the innermost fraction of a parsec of the Galactic centre. For a much larger scale of a few hundred parsec around Sgr A*, I will then discuss an efficient novel formation channel for the provocatively elusive intermediate-mass black holes.

	Promotionskolloquium
Ivalu Barlach Christensen	ORATED

MPIfR

The physical state of the interstellar medium (ISM) is essential for understanding the intricate processes involved in massive star formation within galaxies. The nearby (d about 1.5 kpc) molecular cloud, Cygnus-X, harbors multiples sites of high-mass star-formation, allowing us to probe the various stages as stars form and how the chemistry evolve. Within the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE), we aim to explore the large-scale distribution of deuterated molecules in Cygnus-X. A plethora of star-forming clumps are observed with the CASCADE survey, where clumps are believed to evolve from quiescent infrared-dark clouds to high-mass protostellar objects to hot molecular cores to ultra-compact HII regions. The most active and dense region within Cygnus-X is the DR21 filament, harboring the prominent Hii region DR21 Main with the most intense outflow of the Milky Way. The degree of deuteration, R, can significantly enhance over the elemental D/H-ratio (10^−) depending on physical parameters such as temperature, density, and ionization fraction. Deuterated molecules and their molecular D/H-ratios are important diagnostic tools to study the physical conditions of star-forming regions. This thesis focuses on probing the deuterated fractions of Cygnus-X. Along the DR21 filament, the deuterated fraction of DCO+, DNC, and DCN exhibit morphological variations, caused by the local physical conditions. Active star-formation along the filamentary structure initiate shock chemistry in these high density region, destroying DCO+, and consequently decreasing R(DCO+). Furthermore, the lower density regions are exposed to FUV, in which the formation of HCO+ is halted, consequently increasing the R(DCO+). Finally, to further understand how deuterated fractions behave as clumps evolve, we investigate 67 clumps. Utilizing CASCADE observation of the ubiquitous H2CO complemented with higher J-transitions with the APEX telescope, we determine the physical conditions of 67 clumps in Cygnus-X. The methodology of determining the H2 volume density is efficient in probing the bulk of the gas within 0.2 pc of the clumps. With the physical conditions constrained, we model the chemical evolution of these clumps utilizing the plethora of molecules covered with CASCADE, including the 6 deuterated fractions. We find that the two deuterated fractions decrease and increase, respectively, as the clumps evolve and become hotter.

	Promotionskolloquium
Sarwar Khan	ORATED

MPIfR

High-mass stars (> 8 Msun) play a vital role in shaping galaxies and the interstellar medium (ISM) through their intense radiation, stellar winds, and eventual supernova explosions. Yet, key questions about how they form, influence their surroundings, and regulate future star formation remain open. Studying these stars is challenging as they are rare, short-lived, and form deep inside dusty, distant clouds. Statistical, unbiased surveys are therefore essential, and recent technological advances have made this possible. The first part of this talk presents a blind search for HII regions — ionized regions created by the intense ultraviolet radiation of high mass stars — conducted using radio recombination line and continuum emission from the GLObal view on STAR formation (GLOSTAR) survey. This analysis cataloged 244 Galactic HII regions and derived their physical properties and associations with mid infrared and dust emission to shed light on their evolution. To probe how high mass stars influence their natal environments, we investigated molecular gas properties as traced by H2CO (an important densitometer and thermometer) transitions. While the bulk of the H2CO emission arises from the background source, several targets exhibit multiple components. The secondary components typically showcase broader linewidth tracing higher temperatures, indicative of supersonic, nonthermal motions and turbulent gas probing HII region feedback. Together, these results attempt to provide a comprehensive view of high mass star formation, linking the properties of HII regions and their molecular environments across Galactic scales.

	Special Colloquium
Dr. Parthraj Bambhaniya	ORATED

Institute of Astronomy, Geophysics and Atmospheric Sciences, Univ. São Paulo, Brazil

Recent observations by the Event Horizon Telescope and GRAVITY collaborations of Sagittarius A* at the centre of our Galaxy have generated significant interest in understanding the nature of the central compact object through shadow imaging, accretion dynamics, and precision measurements of S-star orbits. The classical Oppenheimer-Snyder-Dutt model predicts black hole formation through gravitational collapse, while Penrose’s cosmic censorship conjecture (CCC) suggests that the resulting singularity must remain hidden within an event horizon. However, the CCC remains unproven, and more recent gravitational collapse models open the possibility of horizonless supermassive compact objects. In this talk, I will discuss generalized shadow formation conditions for supermassive compact objects and how precise astrometric observations from the GRAVITY and UCLA Galactic Center groups can provide insights into the spacetime geometry near Sgr A*. I will also briefly present some of our recent work on General Relativistic Magnetohydrodynamics (GRMHD) simulations of relativistic accretion flows and magnetized plasma dynamics around compact objects, highlighting their importance for interpreting horizon-scale observations and black hole environments. Finally, I will discuss possible observational tests that may help distinguish black holes from alternative compact objects at the centers of galaxies. Keywords: Black Holes, Compact Objects, Shadows, Accretion Disks, Relativistic Orbits.

	Special Colloquium
Dr Paul F. Goldsmith	ORATED

Jet Propulsion Laboratory, California Institute of Technology

Electromagnetic radiation spans a huge range in frequency and thus wavelength, covering frequencies from kHz to about 10 THz. The technology for generating, transmitting, and receiving electromagnetic radiation naturally depends on the wavelength of interesst, but there are surprpising and impressive connections among the techniques that are employed. The optical regime, characterized by size of elements D>>wavelength, was the first to be developed, beginning in the 17th century. This traditionally considered geometrical optics and only minimally concerned with diffraction. The radio, or RF regime is the other extreme with D<lambda, but not by so much that diffraction can be neglected, and you have to deal with quasioptical propagation. Finally, only in the middle of the 20th century did the guided wave regime, propagation with D approximately lambda, appear and undergo explosive growth impelled by development of radar technology. Understanding the characteristics of these different regimes and how they are related to each other offers many insights into electromagnetic theory and is highly valuable for those designing electromagnetic systems at any wavelength.

	Special Colloquium
Vincent Eberle	ORATED

Max-Planck-Institut für Astrophysik, Garching

Many advances in astronomy and astrophysics rely on high-fidelity imaging of sky emission across multiple wavelengths. Recovering spatially and spectrally correlated signals from noisy, instrumentally degraded data requires sophisticated reconstruction techniques. To enable robust, high-precision Bayesian imaging, we introduce the Universal Bayesian Imaging Kit (UBIK) — a flexible, extensible framework for probabilistic image reconstruction. UBIK is built on Information Field Theory (IFT) and incorporates instrument representation techniques developed specifically for the framework. These methods were first applied to X-ray observations, where they demonstrated strong performance in reconstructing complex emission structures. By combining principled Bayesian inference with tailored instrument modeling, UBIK provides a unified, reproducible platform for multi-wavelength astrophysical imaging, supporting complex prior models, uncertainty quantification, and scalable inference across diverse observational datasets.

	Main Colloquium
Prof. Franco Vazza	ORATED

University of Bologna, Italy

The origin of magnetic fields measured out to several Megaparsec from the centre of clusters of galaxies is not obvious, and can either be ascribed to primordial, or astrophysical processes (or a combination of both). I will review the most updated results on the observational quests to detect magnetic fields on very large scales with radio telescopes, and show how the combination with modern cosmological simulations can suggest a plausible answer to the puzzle. I will also discuss the upcoming science which might become possible thanks to the advent of the Square Kilometre Array, and in combination with other powerful observational probes.

	Special Colloquium
Prof. Kerstin Kunze	ORATED

University of Salamanca

Primordial magnetic fields generated in the very early universe before decoupling have effects on the temperature anisotropies and polarization of the cosmic microwave background (CMB) as well as large scale structure. Their effect on the linear matter power spectrum has implications for the 21 cm line signal. New possibilities to constrain primordial magnetic fields arise with current and upcoming observations of the 21 cm line of neutral hydrogen such as with the Square Kilometre Array Observatory (SKAO). Using 21 cm intensity maps as well as cross correlations of the CMB Doppler mode and the 21 cm signal prospects of constraining primordial cosmic magnetic fields are considered for SKAO and other 21 cm hydrogen line experiments.

	Special Colloquium
Dr. Stefano Berta	ORATED

IRAM Grenoble

The New IRAM KID Array 2 (NIKA2) is a dual-band continuum camera operating at the IRAM 30m telescope on the Sierra Nevada, in Spain. It is equipped with three kilo-pixels arrays of Lumped Element Kinetic Inductance Detectors (LEKID) cooled at 150mK. NIKA2 observes simultaneously at 1.2 and 2.0 mm, and has polarimetry capabilities at 1.2 mm. I will introduce the NIKA2 instrument, its state of the art KIDs technology, its current performance and its bright future. I will then present the most recent science results: NIKA2 studies the magnetic fields of massive star forming regions and supernova remnants, the interplay between star formation and interstellar medium components in nearby galaxies, the structure of the intracluster medium in massive clusters of galaxies, and the evolution of the dust cosmic density all the way back to an epoch when the Universe was less than 1 Gyr old. Join me in this journey across the millimeter sky!

	Special Colloquium
Dr. Sasha Plavin	ORATED

Black Hole Initiative, Harvard University

Blazars exhibit dramatic optical variability, but the precise location of these flares — accretion flow, jet base, or extended jet — remains debated. I present a novel approach using Gaia astrometry together with VLBI to localize the flaring regions directly. Among blazars with strong optical emission from extended jets, I demonstrate a universal pattern: optical flares occur very close to the central engine. These measurements use the latest Gaia DR3 and place a typical flare within ~0.5 mas (a few pc) of the VLBI core position, consistent with an origin in the innermost jet or accretion region. Such a direct localization can constrain electron acceleration and seed photon fields, and provide a model-independent anchor for gamma-ray and higher-energy emission zones. The upcoming Gaia DR4 will bring per-epoch astrometry, sharpening these constraints further.

	Promotionskolloquium
Shilpa Ranchod	ORATED

MPIfR

Magnetic fields are ubiquitous in the Universe and play a key role in galaxy evolution, influencing star formation, cosmic-ray transport, and feedback. Radio polarisation observations provide a powerful probe of cosmic magnetic fields through Faraday rotation. Large samples of polarised radio galaxies enable rotation measure (RM) grids that trace both extragalactic sources and the magnetised interstellar medium of the Milky Way. As modern interferometers push to µJy sensitivities and dramatically increase RM grid densities, interpreting these measurements requires a better understanding of both foreground Faraday effects and the faint polarised source population. This thesis addresses two key aspects for improving RM grid interpretation: (i) the observational biases and physical origins of Faraday complexity at low Galactic latitudes, and (ii) the nature of the extragalactic polarised source population. Using broadband spectro-polarimetric ATCA observations of polarised extragalactic sources, I show that the observed increase in Faraday complexity toward low Galactic latitudes in the SPASS/ATCA catalogue is largely driven by contamination from diffuse Galactic polarised emission. Our relatively higher-resolution observations allow this contamination to be filtered out, revealing that 42% of sources still show Faraday complexity. We find this complexity to be consistent with turbulent injection scales in the Galactic spiral arms and toward the Galactic centre. In addition, I present the linear polarisation component of the VLA-COSMOS 3 GHz survey, yielding the deepest polarised source counts (2.6 µJy/beam) at this frequency to date. Through these broadband observations, we identify the dominant depolarisation mechanisms in this sample and model the frequency dependence of polarised source counts. Furthermore, these results show that even the µJy polarised sky is dominated by active galactic nuclei, with no detection of star-forming galaxies, implying that significantly deeper observations will be required to probe this population, even at higher frequencies.

	Special Colloquium
Prof. Roger Deane	ORATED

Inter-University Institute for Data Intensive Astronomy (IDIA), South Africa

I will present an overview and report early science from the MeerKAT-South Pole Telescope (SPT) Survey, a deep UHF-band eXtra Large Project (XLP) legacy project recently approved to map 800 square degrees of the southern sky to a sensitivity of ~10 uJy/beam. Uniquely designed to exploit the synergy between world-leading observatories at ~1 GHz and ~100 GHz, this survey covers the deepest Cosmic Microwave Background fields in existence. In this talk, I’ll focus on early results from the survey’s first stage: a 100 square degree pilot that has already detected ~300,000 radio sources. I will highlight specific results demonstrating the strong synergy between these cm- and mm-wave telescopes, including the identification of high-redshift (z > 6) dusty star-forming galaxies, radio halos in SZ-selected galaxy clusters, and the discovery of rare phenomena like Odd Radio Circles, X-shaped radio galaxies, high-redshift OH megamasers and Long-Period Transients. Ultimately, this survey will serve as a significant pathfinder for SKA-era galaxy evolution and cosmology, with commensal image-domain transient science. Furthermore, it will provide significant radio legacy value to complement upcoming multi-wavelength campaigns with LSST, Euclid, and the Simons Observatory.

	Promotionskolloquium
Kartik Rajan Neralwar	ORATED

Max-Planck-Institut für Radioastronomie

The interstellar medium (ISM) is a turbulent, multi-phase medium with a hierarchical structure consisting of molecular clouds (MCs), clumps, and cores. Stars form in dense cores and, over their evolution, inject mass, momentum, and energy back into the ISM through stellar feedback processes. I will present a systematic study of the interactions between stellar feedback and molecular gas structures across different spatial scales and evolutionary stages, using the STARFORGE simulations. These simulations follow the evolution of individual giant molecular clouds, while self-consistently modelling protostellar outflows, stellar winds, radiation and supernovae. I will begin by examining the impact of individual feedback mechanisms on high-resolution gas cores identified in the simulated gas density maps. I will then describe the use synthetic 13CO observations to study the evolution of MCs under the influence of stellar feedback as they would appear in observational surveys such as SEDIGISM. Following this, I will introduce a new pipeline developed to track clumps over time capturing their changes, fragmentation and mergers. Finally, I will present deep-learning based results demonstrating how neural networks trained on synthetic data can identify feedback signatures in real observations. Together, these projects provide a framework for interpreting observed trends in the molecular cloud properties, identifying the observational signatures of stellar feedback in molecular gas, and tracing the time evolution of molecular gas structures in galaxies.

	Special Colloquium
Paloma Thevenet	ORATED

Observatoire de Paris

The blazar 3C 66A is known for its optical flux periodicity and complex jet kinematics. Using 22/43 GHz KaVa (KVN and VERA array) observations and 43 GHz VLBA (Very Long Baseline Array) archival data, we have found that its pc-scale jet has a twisted structure and that the inner jet undergoes periodic swings every 11 years. In this talk, we will describe the peculiar characteristics of 3C 66A and delve into possible interpretation scenarios. The multiwavelength flux variability and jet orientation changes hint at a supermassive black hole binary (SMBHB) in which orbital motion and disk-orbit misalignment lead to jet precession. However, combinations of other mechanisms, such as Lense-Thirring disk precession and jet instabilities, could also account for the properties of 3C 66A, underscoring the challenge in robust SMBHB candidate identification.

	Promotionskolloquium
Vieri Bartolini	ORATED

MPIfR

This thesis investigates the physical connection between accretion processes and relativistic jet properties in radio-loud active galactic nuclei (AGN), with emphasis on misaligned AGN (MAGN). By combining multi-frequency VLBI observations up to 88 GHz with long-term γ-ray monitoring from the Fermi Large Area Telescope and ancillary multiwavelength data, this work explores how different accretion regimes influence jet magnetization, internal structure, and high-energy variability. Growing observational evidence indicates that the excitation class and accretion mode play a fundamental role in shaping jet dynamics and radiative behaviour. Therefore, we explore the dichotomy between High-Excitation Galaxies (HEGs), associated with radiatively efficient thin disks, and Low-Excitation Galaxies (LEGs), typically powered by radiatively inefficient accretion flows. MAGN provide an ideal laboratory for this investigation because relativistic and projection effects are reduced, allowing VLBI observations to probe the compact jet base where high-energy emission is expected to originate. A detailed polarimetric analysis of the HEG radio galaxy 3C 111 reveals a complex magnetized parsec-scale jet. Spectral and rotation-measure mapping identify an optically thick feature located approximately 1–2 parsecs from the core that is co-spatial with extremely high Faraday rotation, suggesting an interaction between the jet and a dense clumpy torus cloud. Farther downstream, a significant transverse RM gradient provides strong evidence for a helical magnetic field. These results indicate that the jet in 3C 111 is still strongly magnetized on parsec scales and propagates in a dense environment, possibly providing dense external photon fields for γ-ray production through inverse Compton. The role of the accretion regime is further explored through a comparative multi-epoch and multi-wavelength analysis of the HEG 3C 111 and the LEG 3C 371, two MAGN with similar global properties but markedly different Eddington ratios. The HEG 3C 111 is dominated by superluminal moving knots and is detected in γ-rays primarily during major flares associated with the ejection of new jet features. In contrast, the LEG 3C 371 exhibits predominantly stationary structures that may act as persistent particle acceleration sites, producing steadier high-energy emission. The observed RM evolution and jet kinematics suggest that stronger disk winds in HEGs may stabilize a relativistic spine through mass loading of an outer sheath, whereas weaker winds in LEGs favor the formation of standing recollimation shocks. We propose that the link between accretion mode and jet properties is driven by differences in disk winds: radiatively efficient HEGs produce strong winds that stabilize the spine–sheath jet, enabling extended acceleration and superluminal features, while weaker winds in LEGs leave the spine more unstable, favoring stationary recollimation shocks. Extending the analysis to a sample of nine nearby Fermi-LAT-detected MAGN reveals differences between HEGs and LEGs in core brightness temperatures and variability patterns. HEG cores tend to approach the inverse-Compton limit and exhibit a higher probability of strong γ-ray flaring, while LEG cores remain closer to equipartition and display more persistent, lower-amplitude emission. Limb-brightening, possibly indicative of a spine-sheath velocity stratification, is observed in three of the four LEGs, as well as in the closest HEG, suggesting that the less frequent detection of this feature in HEGs may be due to their average larger distances, resulting in insufficient spatial resolution in VLBI imaging. The results of this thesis support a unified scenario in which the accretion mode is a primary driver of jet internal structure, stability, and high-energy dissipation. The work provides a framework for future large-sample radio–γ studies and offers observational constraints for relativistic magnetohydrodynamic simulations of disk–jet coupling in radio-loud AGN.

	Main Colloquium
Professor Anna Nelles	ORATED

Erlangen Centre for Astroparticle Physics

Cosmic particles such as nuclei and neutrinos populate the Universe from highly abundant solar wind particles to rare cosmic rays of energies exceeding what we can create on Earth. These latter particles are so rare that one needs detectors of several square kilometers in size to measure a meaningful number of them on Earth; a challenging experimental effort. When interacting at Earth, cosmic rays are typically detected with dedicated particle detectors or Cherenkov telescopes. However, it was been know for several decades that they also create measurable radio pulses. I will elaborate on our quest to detect cosmic particles with the new generation of array based radio telescopes such as LOFAR and SKA-Low, as well as dedicated radio neutrino experiments in the ice of Greenland and Antarctica.

	Special Colloquium
Dr. Stamatios Stathopoulos	ORATED

DESY

Active galactic nuclei are multi-scale and multi-messenger systems in which different observables probe different emitting zones. The emission from these objects can be from the vicinity of the central engine (black-hole magnetosphere) to the parsec-scale jet. In this talk I will discuss recent work on time-dependent modeling of particle acceleration and radiation in AGN, with an emphasis on how high-energy and radio signatures can be connected. I will first present a model for magnetospheric current sheets in M87*, motivated by kinetic simulations, and discuss their role in pair enrichment, MeV/X-ray flaring, and proton acceleration. I will then show how time-dependent lepto-hadronic modeling can be used to interpret delayed radio flares in neutrino-associated blazars, focusing on TXS 0506+056. In that case, I will argue that a simple expanding neutrino-emitting blob is insufficient to explain the observed radio behavior, pointing instead to downstream re-acceleration and changes in beaming.

	Special Colloquium
Ciera Sargent	ORATED

Durham University

Red quasars exhibit a higher incidence of compact (galaxy-scale or smaller) radio emission than blue quasars, arising from systems near the radio-loud/radio-quiet threshold. This result cannot be fully explained by the standard orientation model, instead favouring red quasars as a distinct phase in a quasar’s lifecycle, possibly an obscured-to-unobscured transition where low-power jets and/or AGN-driven winds drive away gas and dust. I will show there is an excess of steep-slope radio emission (alpha ~-1) from red quasars with compact radio morphologies over 144 MHz, 1.4 GHz, and 3 GHz. This excess steep radio emission signature is not seen in normal blue quasars (radio compact or extended) or red quasars with extended low-frequency radio emission, which instead show a broad range of radio spectral slopes consistent with a range of different physical processes. I will show that the strength of this excess steep-slope radio emission increases with increasing dust extinction, along with an overall increase in the radio-detection fraction. I argue that this excess steep-slope radio emission is due to shocks between quasar-driven winds/jets and the dusty nuclear-host galaxy environment. The majority (~86%) of the dustiest quasars (E(B-V)>0.4) with steep slopes have radio luminosities consistent with the prediction from a wind-shock model with a wind efficiency of 7%. This agrees with the scenario where these compact red quasars are undergoing a “dusty blow-out” phase, where a compact jet and/or AGN-driven winds interact with a dusty ISM, causing shocks, leading to steep spectral slopes and enhanced radio detection rates.

	Master Colloquium
Dhanraj Risbud	ORATED

MPIfR

Pulsars are highly magnetized neutron stars that rapidly rotate about their rotation axis and emit radio waves. With every rotation, a pulsar’s radio emission, which is highly collimated in the direction of the magnetic axis, sweeps across the line of sight of a distant observer, who can see the radiation as a series of radio “pulses". As their rotation is typically extremely stable, pulsars can be exploited as astrophysical cosmic “clocks” through a technique called “pulsar timing”. The fastest-spinning and most stable pulsars are the so-called “millisecond pulsars” (MSPs), which are pulsars that rotate hundreds of times per second. These are found in abundance in globular clusters (GCs), self-gravitating galactic sub-systems containing up to millions of stars, with very high stellar densities. Their dense environments enhance the formation of binary systems where a pulsar can be spun up (or "recycled") to periods of a few milliseconds by accreting matter from a companion star, hence the large fraction of MSPs found in GCs. In this Master’s thesis project, I carried out a timing analysis of a selection of pulsars residing in two massive globular clusters: M15 and 47 Tucanae. For the globular cluster M15, I conducted a multi-decade pulsar timing analysis of four pulsars, using data taken at the Arecibo and FAST radio telescopes between the years 1989 and 2026. With this extensive dataset, I was able to accurately measure the proper motions and higher-order spin period derivatives for all the four pulsar. These measurements can be related to the accelerations, as well as their variation in time, that the pulsars undergo because of the gravitational potential of the cluster, which could therefore be probed. In the case of the globular cluster 47 Tucanae, I derived the orbital parameters of two binary pulsars that were recently discovered with the MeerKAT radio telescope. One of these pulsars, called 47 Tuc ai, is particularly interesting for its characteristics: it is the only partially recycled pulsar known in the cluster, and has an orbital eccentricity of 0.18, the highest among the all the binaries found in 47 Tucanae. The second pulsar, 47 Tuc af, is an MSP in a compact binary system, belonging to the so-called “black widow” class. The derivation of the orbital parameters allowed us to associate the companion star to an optical source previously identified by the Hubble Space Telescope.

	Promotionskolloquium
Iason Skretas	ORATED

MPIfR

Protostellar outflows mark one of the earliest, and most prominent signs of star formation, and have been detected in both low- and high-mass sources. Protostellar outflows are considered a key part of the process due to their ability to remove excess angular momentum from the protostar-disk system, which enables the accretion of material. They are typically observed via molecular transitions at radio wavelengths, but are also bright in shock excited transitions in the IR regime. Due to their close connection to the accretion process, understanding protostellar outflows is crucial in order to fully describe the formation of stars. Throughout this thesis, I aimed to investigate protostellar outflows in both the mm and IR regime, in order to investigate several of the open questions regarding their nature with a particular focus is placed on the impact of the large-scale environment onto the outflows and using observations from the NOEMA and IRAM 30m telescopes, as well as, observations from the JWST MIRI/MRS instrument. In the first part of this thesis, I studied the outflow activity along the entire DR21 filament, one of the most active, high-mass star-forming regions in the Galaxy. Using the HCO$^+$ $J=1-0$, H$^{13}$CO$^+$ $J=1-0$, and SiO $J=2-1$ observations of the region, taken as part of the CASCADE project, I aimed to identify all protostellar outflows associated with dense molecular clumps along the DR21 ridge and estimate their physical and energetic properties. By comparing the properties of such a sample with the established correlations between outflow and source properties allowed me to investigate whether the extreme nature of the DR21 filament has any impact onto the outflows, and by extension the formation, of its sources. The results showed no clear connection between environment and outflow activity, with the sources in DR21 being indistinguishable to those of an extended literature sample. Notable exception is the outflow of DR21 Main. Subsequently, I take advantage of the unique capabilities of the JWST, to investigate the inner workings of protostellar outflows. Namely, I study the shock excited transitions of H$_2$ along with various atomic and ionic transitions available in the MIRI range for a sample of 5 low-mass protostars in Ophiuchus. My aim with this analysis is to investigate the origin of this shock excitation, through comparisons of the observations with UV irradiated shock models. The analysis revealed the significant contribution of UV emission within these outflows. I found that the origin of this UV emission has to been from within the protostellar outflows themselves, and not from the external environment. Overall, I analyzed outflows from sources across the entire mass regime, using observations in both the mm and IR regime. Throughout the multiple individual results of each project, my analysis showed that the properties of the large scale environment surrounding a forming protostar have little to no influence on the properties of its protostellar outflow. My results therefore suggest that the star formation process is primarily dictated from small scale processes, taking place within the star forming cores, and not impacted by the more extended environment.

	Special Colloquium
Dr. Maciej Wielgus	ORATED

Instituto de Astrofísica de Andalucía-CSIC, Granada, Spain

The current mainstream paradigm in astronomy is that the compact supermassive objects in the centers of galaxies are black holes. There are good reasons to accept this assumption, black holes have an astrophysically viable channel of formation within general relativity and they do explain energetic properties of both bright AGNs and those of low luminosity sources, powered by radiatively-inefficient low mass accretion rate flows. Any alternative object needs to be extremely compact to remain consistent with the Event Horizon Telescope (EHT) constraints on M87$^*$ and Sagittarius A$^*$. But most ultra-compact objects require exotic matter/energy content or suspicious alteration of the theory of gravity, have no viable astrophysical formation channel, or do not admit advection of energy as a cooling mechanism. The latter argument can be particularly awkward for horizonless alternatives, as the accretion flows in M87v and Sagittarius A$^*$ almost certainly are advective cooling dominated. Nonetheless, we do need to keep our minds open. I will discuss the landscape of theoretical ultra-compact alternatives to black holes, such as horizonless singularities, boson stars, and wormholes. I will present recent constraints on such objects derived from the EHT observations, and I will make a daring attempt to answer the question in the talk's title.

	Promotionskolloquium
Thanh Dat Hoang	ORATED

MPIfR

High-mass stars play crucial roles in the evolution of galaxies, but their formation process is still not fully understood. Our work investigates this topic by studying the warm inner gas envelopes around high-mass star-forming regions in the Top100 sample, selected from the brightest cold dust clumps in the unbiased ATLASGAL survey in the Milky Way. Using mid- and high-J transitions of CO and its rare isotopologues 13CO and C18O, the work probes the morphology and kinematic properties of these envelopes across different evolutionary stages. Observing such lines is traditionally difficult, but it becomes more feasible in this work thanks to the advancement of technology at the APEX/CHAMP+ and SOFIA/GREAT instruments. The 13CO(6-5) data obtained with APEX/CHAMP+ reveal correlations between emission and clump properties, indicating that the excitation of this line, which traces the warm envelopes, increases with the evolution of star formation. Envelope morphology, as revealed by 13CO(6-5) integrated intensity maps, appears mostly as a single core in all evolutionary stages, indicating either that the shapes of the envelopes do not evolve with star formation, or that higher angular resolutions observations are needed to resolve such transformations. Radial intensity gradients of the 13CO(6-5) emission are well described by power-law functions, with steeper slopes at evolved stages suggesting rising gas temperature and/or density at the source centre. The envelope kinematics, however, are complex and could be driven by multiple processes such as outflow entrainment, envelope rotation, or inherited motions from larger-scale envelopes. Spectra of high-J CO(11-10) and CO(16-15) lines obtained with SOFIA/GREAT reveal broad wing emission, which we were able to extract. The wing emission appears already in young sources, suggesting the early existence of outflows in high-mass star formation. Radiative transfer modelling with RADEX suggests that shocks are responsible for the excitation of the gas producing the wing emission.

	Special Colloquium
Chanwoo Song	ORATED

KASI, Korea

We measure the angular diameter distance to the blazar TXS 0506+056 to validate blazars as novel distance indicators. The angular diameter distance is determined by combining VLBI angular sizes with linear sizes derived from a variability timescale-size causality argument, where the Doppler factor is constrained by assuming equipartition brightness temperature at flare peaks. Peak flux densities and variability timescales are obtained through flare decomposition of the light curves. To enhance precision, we incorporate 15 GHz single-dish data from the OVRO 40 m telescope (~12 years), which provides a higher cadence than the 15 GHz VLBA data from MOJAVE (~15 years). Using the VLBA core sizes obtained near the flare peaks, distance measurements are consistent with the ΛCDM model prediction (948.2±13.5 Mpc) within 1σ uncertainties. An improvement in uncertainty by a factor of 2–3 is primarily attributed to the high cadence of the OVRO data. We suggest that the best-fit distance is 941+59/-64 Mpc, derived from the largest flare of the VLBA core flare.

	Main Colloquium
Professor Anvar Shukurov	ORATED

Newcastle University

We explore the multi-phase structure and turbulence formed by supernova activity in a spiral galaxy. Parameter values are typical of the Solar neighbourhood of the Milky Way, but we consider how the system changes as the supernova rate increases by a factor of ten in comparison with the Milky Way value. Our local three-dimensional non-ideal MHD simulations with cosmic rays include the effects of galactic differential rotation, density stratification, compressibility, magnetic fields, heating via supernova explosions and parametrised radiative cooling. Of particular focus is the dependence of the system properties and its multiphase structure on the supernova rate. We show that the turbulent velocity in the warm gas varies very little with the supernova rate, remaining transonic, while the cold and hot gas are more strongly affected. However, the turbulence remains transonic or subsonic on all three phases. The interstellar phase boundaries in the pressure-temperature plane (equivalently, in terms of the gas specific entropy) vary weakly with the supernova rate, but the outflow speed increases significantly. The filling fraction of the hot gas increase systematically and significantly with the supernova rate, with the warm gas volume fraction decreasing and the cold gas remaining largely unchanged. The increase in the fractional volume of the hot gas, rather than an enhancement of the turbulent speed, explains the increase in the spectral line widths with the star formation rate. Both magnetic fields and cosmic rays reduce the density contrast between the phases, making the interstellar gas less inhomogeneous. The turbulent magnetic field strength increases across all phases as the supernova rate increases, but the mean field is weakened significantly. Cosmic ray energy density scales linearly with the supernova rate in all phases. Because of the large diffusivity of cosmic rays, their scale height is quite large, so its contribution to driving the gas outflow is only marginal.

	Main Colloquium
Nataliya Porayko	ORATED

Max-Planck-Institut für Radioastronomie

Pulsars, which are very rapidly spinning neutron stars, can be instrumental in solving the puzzle, which has perplexed the minds of the scientific community for almost a century – dark matter (DM). In the talk I will mainly focus on the light DM candidates that can be searched for in pulsar observables. The ultralight scalar field DM (also known as "fuzzy" DM), consisting of bosons with extremely low masses of m ∼ $10^{−22}$ eV, solves some of the problems of the conventional cold DM hypothesis. It was shown by Khmelnitsky and Rubakov (2014) that such DM in the Milky Way induces oscillating gravitational potentials, leaving characteristic imprints in the time of arrivals of radio pulses from pulsars. In addition, the coupling of axion-like particles to photons alters the polarization properties of light, i.e. the plane of polarization of linearly polarized beam propagating through the axion field starts to oscillate with typical frequencies of $10^{-8}$ – $10^{-5}$ Hz (Ivanov et al 2019, Castillo et al. 2022). Searches for these two effects were performed in the data of the European Pulsar Timing Array (EPTA), and stringent constraints on the DM density and coupling constant between photons and axion-like particles have been set. In addition, traces of QCD axions with masses of around ~ mu eV can be searched for with the spectroscopic observations of pulsars. We discuss the systematics and artifacts in pulsar data that can mimic the signal of interest and possible methods to avoid the existing biases. I will conclude with other possible probes for new physics that can be performed with pulsar experiments in the nearest future.

	Special Colloquium
Prof. Dr. Vikram Ravi	ORATED

Caltech, USA

The Deep Synoptic Array (DSA) will be a world-leading radio survey telescope and multi-messenger discovery engine. Operating in the 0.7-2GHz band, the survey speed of the DSA will be unmatched among current or planned radio telescopes, while the sensitivity will be comparable to FAST. This has been enabled by two breakthrough technologies: a low-cost antenna outfitted with ambient-temperature receivers, and a new generation of digital back-end called a "radio camera”. Together with other ongoing all-sky surveys, the DSA will have a major impact on multi-messenger and time-domain astrophysics, and on the study of our cosmic history. It will deliver science-ready polarimetric, spectrally resolved image cubes, pulsar timing data, and commensally carry out transient and pulsar searches. I will provide an overview of the project and its science opportunities, with a focus on pulsar and transient discovery, and cosmology and dark-matter searches. For example, I will highlight certain critical problems in neutron-star formation that motivate order-of-magnitude larger pulsar samples. I will show how the existing sample of 109 fast radio burst (FRB) sources with host-galaxy redshifts already provides competitive measurements of the effects of feedback on the matter power spectrum, foreshadowing an era where FRBs are the leading probe of baryonic physics in cosmological studies. I will show how radio observations can directly probe dark-matter models, and indirectly constrain them via halo counts.

	Main Colloquium
Prof. Ue-Li Pen	ORATED

University of Toronto

PTA’s have reported initial statistical GW signals. We describe coherent analysis of the signal, resulting in polarized sky images with effectively 32 pixels per frequency bin, up from one in the standard HD correlation analysis. This likely results in individual detection of the brightest source(s). With future precision coherent pulsar distances, PTAs are a galactic sized telescope, with arc minute source localization. At these long wavelength, edge-on galaxies present a gravitational diffraction grating, potentially providing a precise cosmological ruler.

	Special Colloquium
Dr. Ming-Tang Chen	ORATED

Academia Sinica

We report the first very long baseline interferometry (VLBI) experiment conducted in the 690 GHz atmospheric window. On 21 November 2024, observations were carried out with the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), and the James Clerk Maxwell Telescope (JCMT), using ALMA’s newly developed Band 9 phasing capability. Fringes were detected on the ALMA–APEX baseline during a scan of the quasar J0423–0120 with a signal-to-noise ratio of ~12 sustained for ~60 s, representing the highest-frequency ground-based VLBI fringe detection reported to date. No fringes were found on the intercontinental ALMA–JCMT baseline despite excellent weather conditions, broadly consistent with sensitivity expectations and baseline performance estimates. The experiment provides the first practical test of VLBI operations in the near-terahertz regime. The ALMA Phasing System maintained stable phasing at Band 9 for approximately 1–2 minutes before gradually degrading under these observing conditions. Independent analysis of the coherence function indicates that the effective integration time was limited to ~20 s by the combined stability of atmospheric phase fluctuations and station frequency standards, consistent with the empirical measurements. These results validate key elements of near-terahertz VLBI operation and demonstrate the feasibility of extending VLBI into the 690 GHz atmospheric window, providing a technical foundation for future experiments at even higher angular resolution.

	Promotionskolloquium
Suryarao Bethapudi	ORATED

MPIfR

Fast Radio Bursts (FRBs) are millisecond duration, finite bandwidth (~100s of MHz) radio transients. This doctoral colloquium, in particular, describes the high frequency (around 5 GHz) and polarimetric studies conducted for a peculiar repeating Fast Radio Burst source (FRB 20180916B) that emits bursts only within specific time windows that themselves repeat every 16.34 days. The high frequency study, done using 100 metre Effelsberg Radio Telescope in 4-6 GHz, yielded the first high frequency detection of bursts and confirmed the frequency dependency of the active windows that was only observed at low frequencies (<1 GHz). This behavior is termed as chromaticity and finds the active windows to arrive early and shrink with increasing observing frequency. The polarimetric studies were conducted using upgraded Giant Metrewave Radio Telescope in 550-750 MHz band, and focused on tracking Rotation Measure (RM) and Polarization Position Angle (PA) variability. The RM is seen to vary in a step-like fashion with two epochs of non-variability between an epoch of variability where the RM varies linearly. The PAs of bursts observed within an four hour window do not vary more than 7 degrees suggesting no significant PA variability on seconds to minutes timescales. The PA variabilities within an active window and across active windows at the same phase are also probed, but are only treated as preliminary at this point. The observed PA variability is used to test dynamical models that explain active window periodicity. The non variability of PA on minutes-hours timescales is shown to rule out precession based models where precessional periodicity explains the active window periodicity. The need for measuring the long term PA variability is made explicit by highlighting the constraints that can be placed by them. Lastly, the FRB source and an intermediate X-ray binary source, Her X 1, are qualitatively compared and their similarities are highlighted.

	Special Colloquium
Dr. Raphael Skalidis	ORATED

Caltech, USA

The interstellar medium (ISM) is a dynamic environment consisting of gas at different phases — from hot ionized plasma to cold molecular clouds. Phase interactions are turbulent and influenced by the omnipresent ISM magnetic field, which regulates the flow of matter, cloud formation, and the initial conditions for star formation. Yet, a unified picture of how turbulence and magnetic fields operate across the different ISM phases remains elusive. In this talk, I will present our efforts, which combine analytical modeling, numerical simulations of magnetized turbulence, and polarization observations to interpret and map the ISM’s turbulent magnetic structures. Our work provides new tools to constrain the three-dimensional geometry of interstellar magnetic fields. With the advent of large-scale polarization surveys, we are entering an era where a truly 3D view of the multiphase, magnetized ISM is within reach.

	Main Colloquium
Professor Dhruba Saikia	ORATED

Tata Institute of Fundamental Research, Pune, India

Active galaxies, which include both starburst galaxies and active galactic nuclei (AGN), are among the most enigmatic objects in our Universe. They emit across the electromagnetic spectrum and there is also increasing evidence of detection of neutrinos from some of them. This presentation will briefly introduce the different kinds of active galaxies, and discuss their emission at the highest energies, namely gamma rays, along with their radio properties. Although the bulk of the extragalactic gamma ray sources have been observed to be associated with blazars, which are believed to have their jets inclined at small angles to the line of sight, a wide and rich variety of active galaxies in significant numbers have been found to be associated with gamma ray sources in recent years. Some of these recent results and their implications will be discussed.

	Special Colloquium
Dr. Ruchi Mishra	ORATED

Institute of Astronomy - Nicolaus Copernicus University, Toruń

We explore the equilibrium shapes of barotropic fluid tori with uniform angular momentum in the gravitational field of a Reissner-Nordström (RN) naked singularity. The RN metric represents a charged, static, spherically symmetric source of gravity. When the charge exceeds the mass, the central object becomes a naked singularity, with unique features such as a "zero-gravity" sphere where test particles can theoretically remain at rest. For fluids with angular momentum, the equilibrium structures are toroidal, either fully or partially outside the zero-gravity sphere, with maximum pressure occurring beyond this sphere. Interestingly, unlike black holes, a fluid cannot accrete onto the singularity; bound fluid remains in orbit within the torus, while unbound fluid escapes to infinity in jet-like outflows. These findings may provide insights into toroidal structures observed in images of Sgr A* and M87 by the Event Horizon Telescope.

	Main Colloquium
Dr. Eda Gjergo	ORATED

Nanjing University

Galactic chemical evolution (GCE) links observed stellar and gas abundances to the sequence of stellar populations that produced that enrichment. I will argue that GCE provides an essential, yet underused, constraint on galaxy evolution and on the assembly of cosmic structure, especially in the Early Universe. Central to any GCE model is the stellar initial mass function (IMF). Observations indicate that the IMF varies with environmental properties, so a galaxy-wide IMF suitable for GCE must encode this dependence. Any attempt to reconstruct an empirically-grounded history of chemical enrichment requires an IMF consistent with observational constraints, yet many GCE models still assume an invariant IMF and a separable birthrate function. In this seminar, I will use the open-source GalCEM code to show how far such models can go, and where they fail, when compared with abundance patterns in our Galaxy and its satellites. I will then summarize evidence for IMF variations with star formation rate and metallicity. I will present the tight empirical correlation between the total stellar mass of a newly formed stellar system and the mass of its most massive star, and I will discuss its possible physical origin. I will conclude by outlining the early chemical enrichment of massive early-type galaxies and why their formation at redshift z > 15 must contribute to the cosmic microwave background.

	Main Colloquium
Professor Axel Brandenburg	ORATED

The Nordic Institute for Theoretical Physics (Nordita), Sweden

Current gamma-ray and radio observations constrain the present-day intergalactic magnetic field to be between 10^{-16} and 10^{-9} gauss on parsec to megaparsec scales. Their filling factors in the voids between galaxy clusters must have exceeded 10 to 30 percent, making it unlikely to be produced by astrophysical mechanisms. A magnetic field of primordial origin could have been generated in the first microseconds of the Universe during inflation or the subsequent electroweak or quark confinement epochs. Its comoving strength and typical scale are or will be reflected in the spectrum of relic gravitational waves on millihertz to nanohertz frequencies. Between generation and present-day observation, the magnetic field must have evolved on a specific track in a diagnostic diagram of comoving field strength versus length scale. This evolution is described by decaying homogeneous magnetically dominated turbulence. This is the subject of high-resolution direct numerical simulations covering over 28 orders of magnitude in cosmic time, augmented by an improved theoretical understanding of the turbulent decay. However, there are still some theoretical questions such as the effects of reconnection, and there are numerical challenges, so we need to ask when can we trust the simulations. Also, how are the results affected by additional physics such as the detailed generation mechanism, for example through axion-like particles, and during the time of recombination, they must include the interaction between photons, baryons, as well as dark matter, and of course the changing expansion of the universe. In my talk, I will review these recent developments and discuss ways of addressing them.

	Special Colloquium
Yu-sik Kim	ORATED

Ulsan National Institute of Science and Technology (UNIST), Korea

High-energy cosmic neutrinos, owing to their weak interactions with matter, offer a powerful means of probing extreme particle acceleration processes that cannot be directly accessed through electromagnetic observations. On 8 December 2021, the IceCube Neutrino Observatory reported the detection of a sub-PeV extragalactic neutrino event, IC-211208A. The blazar PKS 0735+178 lies within the localization region of this event and has therefore been considered a strong candidate neutrino-emitting source, joining a small group of extragalactic objects plausibly associated with TeV–PeV neutrinos. In this talk, I present a comprehensive investigation of the multi-wavelength variability and parsec-scale jet evolution of PKS 0735+178 across the neutrino detection epoch. This study combines radio VLBI observations with contemporaneous optical (ASAS-SN g and V bands), X-ray (Swift/XRT), and γ-ray (Fermi-LAT) data to trace the temporal and structural response of the jet. The neutrino arrival coincides with pronounced broadband flaring activity extending from radio to γ-ray energies. On VLBI scales, a newly ejected jet component appears shortly before IC-211208A and subsequently interacts with a quasi-stationary downstream feature at the time of the neutrino event. We interpret this temporal and spatial coincidence as evidence for efficient particle acceleration associated with a recollimation shock, where proton entrainment may occur. The inferred location of the neutrino-emitting region is at a projected distance exceeding approximately 6.5 pc from the central engine, supporting a scenario in which high-energy neutrino production takes place well downstream of the VLBI core. We will also then introduce recent and ongoing VLBI observations of PKS 1749+096, which is considered a new neutrino candidate. Finally, I will provide a concise overview of preparations for a KVN Key Science Program motivated by these investigations.

	Special Colloquium
Prof. Andrew Zentner	ORATED

University of Pittsburgh, USA

Dark matter halos provide the gravitational framework within which galaxies form and evolve, and thus underpin the observed large-scale structure of the Universe. Within the cold dark matter (CDM) paradigm, the growth and clustering of halos are well understood in broad terms, making halo clustering a natural starting point for understanding galaxy clustering. While halo clustering has long been known to depend strongly on halo mass, it has become clear over the past two decades that halos also cluster differentially at fixed mass as a function of additional properties such as formation time, concentration, and accretion history. This phenomenon, commonly referred to as assembly bias, has important implications for models of the galaxy–halo connection. If galaxy occupation depends on halo properties beyond mass alone, then mass-only models cannot describe galaxy clustering at high precision, potentially introducing both scatter and systematic biases into inferred galaxy–halo relations and cosmological constraints. I will briefly review the theoretical origin of assembly bias and its impact on halo and galaxy clustering. I will then present two recent observational detections of halo assembly bias in SDSS and DESI data obtained by my collaborators and me, and argue that these signals provide direct, testable evidence for environment-dependent halo and galaxy evolution. I will then introduce a new aspect of assembly bias related to satellite systems. Large galaxies are surrounded by populations of satellite galaxies whose spatial distributions are often highly anisotropic. Using numerical simulations within the CDM framework, I will show that subhalos around host halos are distributed far more anisotropically than the underlying dark matter. I will further present recent results demonstrating that host halo clustering depends on the degree of anisotropy or planarity in their satellite populations, implying a clear environmental dependence of satellite configurations. These findings may have important implications for observational tests of satellite anisotropy and for other large-scale structure observations such as intrinsic alignments in weak gravitational lensing.

	Master Colloquium
Josephine Benna	ORATED

MPIfR

Canonical wisdom has the molecular gas in galaxies distributed following simple exponential profiles, with a half-light radius related to the optical size. There is however ample evidence that this is an over-simplification, with actual molecular gas distributions displaying a much broader range of shapes and sizes. In this thesis I calculate the non-parametric morphology parameters Concentration, Asymmetry, Smoothness, Gini, and the moment of light (CASGM) for all detected galaxies in the KILOGAS sample using the high-resolution CO(2-1) observations from the Atacama Large Millimetre/submillimetre Array (ALMA) to quantify the morphology of the molecular gas in nearby disc galaxies, and investigate its connection to global galactic properties. I do this through the use of statistical methods such as the spearman rank coefficient and a random forest regression.

	SFB Colloquium
Prof. Amelie Saintonge	ORATED

MPIfR

The interstellar medium plays a central role in the galaxy evolution process; it is the reservoir that fuels galaxy growth via star formation, the repository of material formed by these stars, and a sensitive tracer of internal and external processes that affect entire galaxies (e.g. accretion and feedback). This overview talk will discuss how observations of the interstellar medium are shedding light on the vast range of physics and scales at play in the star formation and galaxy evolution processes, using results from recent observing campaigns with (sub)mm/radio facilities (IRAM, ALMA, JCMT, APEX) as well as large optical spectroscopic surveys (DESI). In particular, I will introduce KILOGAS, a new large ALMA survey providing a kiloparsec-scale view of the molecular gas in a large and representative sample of 500 nearby galaxies. The survey is unveiling the diversity of the morphology of molecular gas discs and orders of magnitude differences in the efficiency of star formation out of this gas.

	Main Colloquium
Professor Caroline Heneka	ORATED

University of Heidelberg

The era of radio astronomy is rapidly transforming as next-generation instruments, in particular the Square Kilometre Array (SKA), begin to map vast portions of the observable Universe. These surveys generate enormous and complex datasets, from millions of galaxies across cosmic time to mappings of the intergalactic medium and large-scale structure via the 21cm background during the Epoch of Reionization. Modern AI and machine learning methods are becoming essential for extracting scientific insight from these data. In this talk, I will highlight how flexible, data-driven approaches enable robust scientific analyses across the full workflow from simulations and observational modeling to inference, and show how they help to gain insights on galaxy evolution, the properties of the intergalactic medium, and fundamental physics, while accelerating discovery across large radio surveys.

	Master Colloquium
Henrik Silas Alt	ORATED

MPIfR

Sideband separating receivers (2SB) are a widely used type of heterodyne receivers in radio astronomical observations, allowing the simultaneous observation of the lower and upper sideband. However, phase- and amplitude imbalances of the signals limit the achievable sideband-separation ratio (SRR) of these receivers, caused by imperfections of the analog components. This thesis presents a processing-pipeline for digitally compensating these analog imperfections, by determining and applying imbalance-compensating parameters in combination with a digital implementation of an IF-hybrid. The processing-pipeline was tested with synthetic data, a low-frequency test-setup with frequencies below 10 GHz and a high-frequency test-cryostat setup, operated in the mm/submm regime around 340 GHz, showing a clear improvement in sideband separation for all test-cases.