Magnetic fields and jets: a love-hate relationship?

Special Colloquium
Prof. Dr. Manel Perucho
ORATED
Universitat de València, Spain

I will review a series of relevant processes involving magnetic fields in relativistic jets from the basis of new simulations and the role the field can play in jet evolution at the sub-pc to sub-kpc scales. In particular, I will discuss different aspects of jet acceleration and collimation, the implications of jet magnetization for long-term stability, and the interplay between the magnetic energy flux and the other main outflow energy channels, namely, internal and kinetic energy fluxes.

Exploring the transient landscape with MeerKAT: from FRBs to ultra-long period neutron stars

Main Colloquium
Dr. Manisha Caleb
ORATED
University of Sydney

Fast radio bursts (FRBs) have a story which has been told and retold many times over the past few years as they have sparked excitement and controversy since the pioneering discovery in 2007. The FRB class encompasses a number of microsecond to millisecond duration pulses occurring at Galactic to cosmological distances with energies spanning several orders of magnitude. Many radio telescopes around the world are currently undertaking wide area surveys and targeted searches to discover and localise FRBs, as their true potential can only be realised up host galaxy identification and association. Significant effort is being put into localising FRBs to sub-arcsecond precision by radio interferometers around the globe. The MeerTRAP project at the MeerKAT telescope in South Africa has been operational since 2019 and has discovered ~35 FRBs and localised a handful of them to host galaxies, including an FRB localised to sub-arcsecond precision at z~1. In this talk, I will present the recent discoveries from the MeerTRAP project, their multi-wavelength follow-up efforts and the possibility of ultra-long period magnetars being FRB progenitors.

The effects of stellar feedback on molecular clumps in the Lagoon nebula (M8)

Master Colloquium
Angelique Kahle
ORATED
MPIfR

The Lagoon nebula (M8) is known as one of the brightest HII regions in the sky, which hosts several O-stars and regions of recent and ongoing star formation. With M8-Main and M8 East, two prominent regions of massive star formation have been studied in detail in recent years, while large parts of the nebula have remained mostly unexplored to this date. Aiming to analyze the effects of stellar feedback from massive stars on the remnant molecular gas in M8, we conducted spectroscopic observations on all 37 known molecular clumps using the Atacama Pathfinder Experiment (APEX) and the IRAM 30 meter telescope. We observe a large chemical variety and interesting kinematic differences between the molecular clumps, which are largely composed of multiple physical components. Signs of star formation are detected at the majority of the clumps, while we also trace the presence of photon dominated regions across the entire nebula. Spectral energy distributions derived from archival continuum maps suggest that the observed clumps are less massive and warmer compared to the ATLASGAL sample of clumps in the inner galaxy. While the increased clump temperatures may be caused by external heating from the nearby O-stars, this feedback does not prevent the nebula from forming a new generation of stars.

Sagittarius A* in its natural habitat

Main Colloquium
Dr. Elena Murchikova
ORATED
Institute for Advanced Study, Princeton, USA

The Milky Way’s Galactic Center black hole Sagittarius A* is the closest to us supermassive black hole. It is an ideal candidate to explore near horizon effects, to test alternative theories of gravity, and to learn the mechanics of black hole feeding, accretion, and feedback -- forces shaping galaxies and the Universe as a whole. Despite its proximity, the accretion flow onto it is not well understood. At large scales (10^5 R_sch and beyond), the primary source of information about accretion flow comes from observations of hot X-ray emitting gas. At near horizon scales, the density of the flow is constrained by polarization measurements and EHT. At intermediate scales, there are too few model-independent probes to reliably determine physical properties of the gas, which complicates the search for the right model for the black hole accretion model. In 2019, using ALMA observations I discovered a disk of cool gas at intermediate distances (10^4 R_sch) from the black hole, which provides new clues to the physics of the inner accretion flow of the Sagittarius A*. In this talk, I will review what is known about the structure of the accretion flow around the black hole. I will discuss the properties of the cool disk and what we can learn from it about the structure of the accretion flow. I will show our new realistic simulations of the inner two parsecs of the Galactic Center which, for the first time, captures Sagittarius A*’s multiphase accretion physics, and discuss the so-called submm variability crisis.

MeerKAT observations of star-forming galaxies active galactic nuclei up to z=5

Special Colloquium
Dr. Sthabile Kolwa
ORATED
University of Johannesburg, South Africa

The South African MeerKAT radio telescope's inauguration in July 2018 marked the beginning of science operations for the 64 antenna array. Since then, MeerKAT data has been accessible to the astronomy community through MeerKAT Open Calls every two years. Additionally, eight large-scale survey projects (LSPs), each with their own distinct science goals, have been established with the aim of exploiting MeerKAT's full potential in producing noteworthy scientific results. One such LSP is MIGHTEE (MeerKAT International GHz Tiered Extragalactic Exploration) which uses deep (~10 microJy sensitivity), wide-field radio continuum surveys to investigate galaxy formation and evolution. Early science images of the XMM-LSS and COSMOS fields in the MeerKAT L-band in addition to multiwavelength ancillary detections from legacy surveys in the optical, infrared and X-ray, are instrumental in constraining the physical properties of radio active galactic nuclei (AGN) and star-forming galaxies (SFG) over redshifts of 0 < z < 5. In this talk, we will go over recent Early Science results from the MIGHTEE group and demonstrate their impact in enhancing our understanding of galaxy evolution at cosmic noon and approaching the epoch of reionisaiton.

Diverse and puzzling radio nature of narrow-line Seyfert 1 galaxies

Special Colloquium
Dr. Emilia Järvelä
ORATED
ESAC/Spain

Narrow-line Seyfert 1 (NLS1) galaxies are a subclass of active galactic nuclei (AGN) identified more than 30 years ago, but still not well understood. Their most distinctive feature is the narrowness of their permitted lines, attributed to low rotational velocity around a relatively low-mass supermassive black hole. With luminosities comparable to those of typical broad-line Seyfert 1 galaxies, they consequently have high Eddington ratios, indicating that their central black holes are growing fast. Some NLS1s have also been detected in gamma-rays, proving that they are able to harbour powerful relativistic jets. In this talk I will focus on the properties of NLS1s' radio emission, with emphasis on the recent studies about its diverse nature, and the surprising discovery of relativistic jets that seem to be totally absorbed at low radio frequencies. I will discuss how the presence of relativistic jets in NLS1s affects our understanding of jet phenomena, and what possible implications the existence of absorbed jets might have in the grand AGN scheme.

Galactic contribution to the high-energy neutrino flux found in track-like IceCube events

Lunch Colloquium
Prof. Dr. Yuri Y. Kovalev
ORATED
MPI für Radioastronomie

Context: Astrophysical sources of neutrinos detected by large-scale neutrino telescopes remain uncertain. While there exist statistically significant observational indications that a part of the neutrino flux is produced by blazars, numerous theoretical studies suggest also the presence of potential Galactic point sources. Some of them have been observed in gamma rays above 100 TeV. Moreover, cosmic-ray interactions in the Galactic disk guarantee a diffuse neutrino flux. However, these Galactic neutrinos have not been unambiguously detected so far. Aims: Here we examine whether such a Galactic component is present among the observed neutrinos of the highest energies. Methods: We analyze public track-like IceCube events with estimated neutrino energies above 200 TeV. We examine the distribution of arrival directions of these neutrinos in the Galactic latitude b with the help of a simple unbinned, non-parametric test statistics, the median |b| over the sample. Results: This distribution deviates from that implied by the null hypothesis of the neutrino flux isotropy, and is shifted towards lower |b| with the p-value of 4*10^{-5}, corresponding to the statistical significance of 4.1 sigma. Conclusions: There exists a significant component of the high-energy neutrino flux of Galactic origin, matching well the multi-messenger expectations from Tibet-ASgamma observations of diffuse Galactic gamma rays at hundreds of TeV. Together with the previously established extragalactic associations, the Galactic component we report here implies that the neutrino sky is rich and is composed of contributions from various classes of sources.

The key role of astrochemistry in driving planet formation and habitability

SFB Colloquium
Prof. L. Ilsedore Cleeves
ORATED
University of Virginia, Charlottesville, USA

Historically, our perspective on how planets form and obtain their compositions has been motivated by our Solar System. However, we are just one system, and missions like Kepler and TESS have revealed a variety of planetary types and architectures. How do we fit in? In the last five years, the Atacama Large Millimeter Array has revolutionized our understanding of planet formation by observing the process at high spatial resolution (reaching in some cases ~au scales) matched with unprecedented sensitivity at radio wavelengths. In this presentation, I will review recent highlights from the TW Hya as a Chemical Rosetta Stone ALMA project and discuss how these findings both confirm and, in some ways, challenge our current picture of the chemistry of planet formation.

Harnessing the opportunities in the approaching radio astronomy renaissance.

Main Colloquium
Prof. Jessica Dempsey
ORATED
Netherlands Institute for Radio Astronomy (ASTRON)

ASTRON, and MPifR, stand on an exciting new horizon as we all face the upcoming opportunities in radio astronomy. ASTRON leading the Netherlands partnership in SKA and the upcoming ERIC for LOFAR. We are also looking to the challenges and opportunities in overcoming the daunting data bottlenecks from collection, processing to providing easily accessible science-ready data products to our community. In these ways, ASTRON and MPifR have more in common in our future goals than perhaps ever before. ASTRON is taking the coming year to develop its mid- and long-term vision, strategic plan and technology and science development needs. I will present the preliminary shape of these discussions, and where we hope to further strengthen our collaborations with MPifR as we step into this decade of radio astronomy renaissance.

Automation of VLBI

Special Colloquium
Dr. Leonid Petrov
ORATED
NASA Goddard Space Flight Center, USA

VLBI technique emerged over 50 years ago, but it still cannot be viewed as mature as other space geodesy techniques, because its scheduling, operation, and data analysis still requires a great deal of manual work. I will talk about my work on automation of VLBI scheduling, automation of post-processing, automation of geodesy/astrometry analysis, and automation of imaging.

Resolve: Polarimetric, time-variable and multi-frequency Bayesian imaging of VLBI data

Special Colloquium
Dr. Philipp Arras
ORATED
MPI for Astrophysics

Radio-interferometric observations are inherently incomplete, as they only sparsely probe the Fourier components of a source on the sky. In order to recover the original source structure from noisy and incomplete data it is necessary to solve an inverse problem. Unfortunately there is an infinite number of images that are compatible with the data. The Resolve algorithm approaches the problem from a probabilistic perspective by imposing a prior model over plausible source configurations and combines this information with the likelihood of the data in order to obtain a probability distribution of possible source configurations that are a priori plausible and compatible with the data. The method is based on Gaussian processes with adaptive kernels and can be extended to multi-frequency, dynamic, as well as polarisation imaging tasks. It can make use of regular visibility data, as well as closure quantities and can also accommodate for self-calibration. We will showcase several examples, including reconstructions of M87* EHT 2017 data and ngEHT imaging Challenge reconstructions.

The dense interstellar medium and star formation across the nearby galaxies NGC 3627 and NGC 253

Promotionskolloquium
Ivana Bešlić
ORATED
Argelander Institute for Astronomy

The star formation process is an essential aspect of galaxy evolution. Observations of star-forming regions from sub-pc to kpc scales revealed a tight correlation between star formation and the emission of high-critical density molecules (HCN, HNC and HCO+). However, it is still unclear whether stars can form in regions where gas is overall denser or whether this gas is notably more efficient at producing stars. The missing piece in the star formation puzzle lies in understanding the properties of dense molecular gas at giant molecular cloud scales. Compared to the CO emission, high-critical density lines are faint, making them difficult to detect and approaching the sensitivity limits of current observing facilities. Despite recent major efforts to map molecular emission traced by the CO molecule at cloud scales, we still lack an equivalent study of high-critical molecular lines at these scales, covering a set of environments across nearby galaxies. In this doctoral thesis, we expand the previous efforts in recent extragalactic studies to bridge the gap between our knowledge of star formation in the Milky Way and across unresolved systems at high redshifts. This study presents the first attempt to constrain the role of dense molecular gas at a few hundred pc and its relation to star formation across two nearby galaxies, NGC 3627 and NGC 253, using observations of high-critical density molecular lines within the 3 mm regime obtained by NOEMA and ALMA. The major results of this doctoral thesis are that the intensity ratio of high-critical density lines (i.e. HCN) to the CO(2-1) appears sensitive to molecular cloud surface density changes, which makes them an excellent tool for constraining the density contrast. In studying the star formation efficiency of dense molecular gas, we found that environmental conditions play a crucial role. For example, the centres of NGC 3627 and NGC 253 contain the largest amount of dense molecular gas, yet their star formation efficiency is significantly reduced, whereas we found more efficient gas in other regions of these galaxies, such as in the bar ends, ring and spiral arms. Our results could be a result of the kinematics of dense molecular gas playing a critical role in setting the ability of gas to form stars. The complex kinematics observed in the centre and bar of NGC 253 show that it can significantly decrease this dense gas star formation efficiency while converging dense gas flows can further enhance the star formation process, as seen in the bar ends of NGC 3627. The results presented in this doctoral thesis further support the importance of understanding the properties of dense molecular gas in nearby galaxies. Together with the turbulent theory of star formation, the emission of these high-critical density lines relative to the mean gas densities and the role of the environment are essential drivers of local star formation at scales of molecular clouds. This work outlines the importance of obtaining a clearer picture of the dense interstellar medium, which is the major contributor to the baryon cycle of galaxies that ultimately dominates their cosmic evolution.

The Galactic centre: structure, dynamics and star formation of a unique astrophysical target

Main Colloquium
Dr. Mattia Sormani
ORATED
Universität Heidelberg

I will give an introduction to the structure, dynamics and star formation in the centre of the Milky Way. After reviewing the basic theoretical tools, I will discuss several topics including (i) how can we interpret large-scale spectral line datacubes of CO, HI and other interstellar gas tracers in the context of gas flowing in the strongly non-axisymmetric gravitational potential of the Galactic bar; (ii) how can we use the gas dynamics to constrain the properties of the Galactic bar; (iii) what physical processes transport the gas inwards from the Galactic disc (R~3 kpc) to the Central Molecular Zone (CMZ, R~120 pc) and then to the central black hole SgrA*; (iv) what is the spatial and temporal distribution of star formation in the Galactic centre; (v) what are the structure, dynamics and secular evolution of the Nuclear Stellar Disc, the flattened stellar structure that dominates the gravitational potential at Galactocentric radii R between 30 pc and 300 pc. Finally, I will highlight some open questions and directions of future research.

Molecular diversity in early stage high-mass protostars

Promotionskolloquium
Laure Bouscasse
ORATED
MPIfR

The physical processes at the origin of high-mass stars are still poorly constrained. ALMA has been extremely successful to identify a large sample of high-mass protostars in early evolutionary stages (high-mass equivalents of Class 0 protostars) in the frame of the SPARKS survey (Csengeri et al. 2018, 2019). From these, six sources have been found to be isolated down to 400au, which were selected to study the early warm-up phase chemistry leading to the emergence of hot cores. These sources have been studied using an unbiased spectral survey between 159 and 374 GHz with the APEX telescope and revealed a rich molecular emission even towards the youngest sources. Towards all the sources, on average 40 species were identified including molecular ions, complex organic molecules (COMs) and several deuterated species. We located these species within the envelope by combining a detailed analysis of the line profiles with local thermodynamic equilibrium modeling. While some objects exhibit a clear structure with a well-defined warm gas phase, some remain mostly cold with warm gas traced only by methanol and methyl cyanide. Although the sources have a common molecular reservoir composed of the simplest molecules, we detect COMs in the cold component of the envelope for all objects. We find that one of the main differences in the molecular emission of our sources is for the COMs. We pinpoint a gradual emergence of the warm component and an increasing molecular complexity along the evolutionary sequence of the targets. The comparison of the molecular composition of our objects to that of a sample of hot cores and hot corinos suggests strong similarities for O-bearing COMs. Overall, we propose a new evolutionary stage prior to the emergence of hot cores, where molecular abundances of COMs are lower than that of hot cores and resemble more that of hot corinos. [Referees: Prof. Dr. Karl M. Menten, Prof. Dr. Pavel Kroupa, Prof. Dr. Klaus Desch, Prof. Dr. Leonie Esters]

A shocking shift in paradigm for classical novae

Main Colloquium
Prof. Laura Chomiuk
ORATED
Michigan State University, USA

Over the last decade, our understanding of classical novae has been turned on its head with the discovery of gamma-rays from Galactic eruptions. This discovery has highlighted the value of novae -- non-terminal, thermonuclear eruptions on the surfaces of white dwarfs in binary systems -- as laboratories for studying shocks and particle acceleration. I will discuss where and how shocks form in the nova ejecta, why we think the shocks may actually dominate the energy budget of the nova eruption, and some of the consequences of the shocks, including dust formation and acceleration of particles to very high (TeV) energies. These recent developments place novae amongst the ranks of interaction-powered transients, making them nearby, common examples of the physics that governs more exotic events like Type IIn supernovae, stellar mergers, and tidal disruption events.

The Renaissance of Astrophysics: a landscape of opportunities in the era of Time Domain Multi-Messenger investigations

Special Colloquium
Prof. Dr. Raffaella Margutti
ORATED
University of California, Berkeley

Astronomical transients are signposts of catastrophic events in space, including the most extreme stellar deaths, stellar tidal disruptions by supermassive black holes, and mergers of compact objects. Thanks to new and improved observational facilities we can now sample the night sky with unprecedented temporal cadence and sensitivity across the electromagnetic spectrum and beyond. This effort has led to the discovery of new types of astronomical transients, revolutionized our understanding of phenomena that we thought we already knew, and enabled the first insights into the physics of neutron star mergers with gravitational waves and light. In this talk I will review some very recent developments that resulted from our capability to acquire a truly panchromatic view of transient astrophysical phenomena. I will focus on two key areas of ignorance in the field: (i) What are the progenitors of stellar explosions and what happens in the last centuries before death? (ii) What is the nature of the compact objects produced by these explosions and what happens when compact objects merge? The unique combination of Discovery Power (guaranteed by planned transient surveys across the electromagnetic spectrum, combined with efforts in the realm of artificial intelligence) and Understanding (enabled by multi-messenger observations) is what positions time-domain astrophysics for major advances in the near future.

The latest puzzle in narrow-line Seyfert 1 galaxies: invisible jets?

Main Colloquium
Dr. Marco Berton
ORATED
European Southern Observatory, Santiago, Chile

Narrow-line Seyfert 1 (NLS1) galaxies are a subclass of active galactic nuclei (AGN) identified more than 30 years ago, but still not entirely understood. These objects are likely characterized by rapidly growing low-mass black holes. Interestingly enough, some of them have been detected in gamma-rays, a sign that they can harbor powerful relativistic jets. In my talk I will review their properties, showing how the true nature of NLS1s is that of early-stage AGN in a recently triggered activity phase, and how they are connected to other classes of kinematically young jetted AGN. I will also report on the discovery, in a handful of NLS1s, of relativistic jets remarkably faint at low radio frequency, but extremely bright and variable at high radio frequency. New observations of these sources are revealing an increasingly complicated picture, and I will outline the different scenarios we are developing to explain this new, unexpected phenomenon.

A comprehensive analysis of the nucleus of the radio source 3C 84 with VLBI

Promotionskolloquium
Georgios F. Paraschos
ORATED
Max-Planck-Institut für Radioastronomie, Bonn, Germany

In this presentation, I will discuss our results from studying the radio source 3C 84 associated with the active galactic nucleus of the galaxy NGC 1275. The focus is put on high-frequency very-long-baseline interferometry studies, which provide the resolution to explore the innermost regions of the observed core-jet morphology. Data observed at three wavelengths (20, 7, and 3.5 mm) have been combined to probe the emission and absorption of the synchrotron radiation and the magnetic field configuration: the spectral index of the central region reveals a gradient (values range between +2 and -1.5 between 7 and 3.5mm), the jet apex is about 400-1500 Schwarzschild radii upstream of the 3.5-mm core, and the magnetic field appears to be a combination between poloidal and toroidal, with a strength of 2–4 Gauss. Imaging results of the central region at 3.5-mm are also presented, further constraining the position of the jet apex. The analysis reveal a possible change of the viewing angle of the relativistic flow, with an upper limit of 35 degrees. Images of the source over 20 years reveal the kinematics of the plasma regions, as well as the jet shape: the latter appears to be frequency dependent, caused by a spine-sheath jet stratification scenario. The spectral index between 7 and 3.5 mm shows a gradient, suggesting the black hole to be off-centered from the total intensity radio maximum. Note: Talk presented at the Seminar Room 1 of the I. Physikalischen Institut of the Universität zu Köln

The tail of the cannonball pulsar J0002+6216

Main Colloquium
Dr. Frank Schinzel
ORATED
NRAO, USA

Studying the dynamics inside complex supernova environments is challenging. Following a supernova explosion, a newly formed pulsar is embedded in the ambient medium. In rare cases, the pulsar can get a significant 'kick' from the initial explosion and may escape its surrounding supernova remnant to interact with the interstellar medium (ISM). This talk will discuss probably one of the best of such cases recently discovered. I will be illustrating the journey that led to the discovery of the pulsar wind nebula (PWN) related to the high 'kick' velocity PSR J0002+6216, followed by a discussion of our recent results from spatially resolved X-ray observations taken with the Chandra X-ray observatory and combined with multi-epoch multi-frequency radio observations with the Very Large Array. These observations are providing unique insights into the bow-shock properties of this PWN and the interaction of the cometary-like tail with the ISM surrounding the supernova remnant CTB 1. I will also include a brief summary of the challenging High Sensitivity Array (VLBA+VLA+Effelsberg) observations, concluded this July, to constrain the parallax distance to PSR J0002+6216. I will end with an outlook addressing a missing population of young gamma-ray pulsars in the Galactic plane, with the potential of finding more young pulsars with rare properties.

The Sardinia Radio Telescope towards operations at high radio frequencies

Special Colloquium
Sergio Poppi
ORATED
INAF, Osservatorio Astronomico di Cagliari, Italy

The Sardinia Radio Telescope (SRT) is a 64-metre single dish radio telescope operating from 300 MHz to 26.5 GHz. In 2019 the Italian National Institute for Astrophysics (INAF) was awarded funds to extend the infrastructure to observe at high frequencies, up to 116 GHz, either in single-dish or VLBI mode. Thus, in this presentation it will be shown the upgrade of the SRT which includes state-of-the-art receivers, back-end, high-performance computing, a new metrology system and also, new instrumentation for laboratories.

SIMPLIFI: A legacy investigation of interstellar magnetic polarization in star forming filaments

Main Colloquium
Dr. Thushara Pillai
ORATED
MIT Haystack Observatory, USA

Stars form during gravitational collapse in molecular clouds. This process governs how galaxies evolve over cosmic time by creating their stellar components. It also affects properties of the planets formed along with the young stars. Collapse in molecular clouds during star formation is controlled by self–gravity, random “turbulent” gas motions inside clouds, and interstellar magnetic fields. Past studies have revealed a detailed picture of the role of self–gravity and gas kinematics during star formation — but observational assessments of magnetic fields remain challenging. A coordinated and ambitious project is needed to systematically fill the gaps in our current understanding of magnetic fields in star formation. SIMPLIFI (“Study of Interstellar Magnetic Polarization: a Legacy Investigation of FIlaments”) is primarily a SOFIA legacy project designed to study a sample of molecular clouds at near (d < 500 pc) and intermediate (d <5 kpc) distances in polarized Far-IR light. Near-IR starlight polarization combined with Gaia data provide information on the connection of dense clouds to its diffuse natal environment. SIMPLIFI also uses molecular line emission to study the relative alignment of gas flows and magnetic fields and tests key theoretical predictions of MHD turbulence. I will present highlights from the pilot survey program that start to clarify the role of magnetic fields in a diverse sample of star-forming filaments, and provide a framework to simplify the diversity of filament properties.

The AMISS survey: Understanding CO(2-1) as a molecular gas tracer

Special Colloquium
Ryan Keenan
ORATED
University of Arizona, Tucson, USA

The J=1-0 transition of the CO line has long been the canonical tracer of molecular gas. However, the improved sub/millimeter facilities, the push for higher resolution, and a growing interest in high redshifts all favor observations with the higher frequency CO(2-1) line. Recent studies have found evidence that CO(2-1)-CO(1-0) line ratios vary between galaxies of different types and across galactic environments, suggesting that care is needed when interpreting CO(2-1) as a tracer of bulk molecular gas. These results are complicated considerably by the difficulty of comparing millimeter data collected with different facilities. Calibration issues produce systematic uncertainties comparable to the dynamic range of trends found in recent studies and resolved measurements can produce contradictory results depending on the datasets used. I will present the Arizona Molecular ISM Survey with the SMT (AMISS), a multi-CO line survey of ~200 nearby galaxies designed to understand CO line ratios across a broad range of galaxy properties. AMISS uses data from a single telescope for each line, with careful attention to calibration, which allows us to overcome many of the challenges in measuring line ratios. The large size of our survey allows us to identify trends between galaxy properties and CO line ratios. In particular we find a correlation between CO(2-1)/CO(1-0) and galaxy-integrated star formation rate. This effect propagates to the slope of the Kennicutt-Schmidt relation, giving different slopes for measurements made with different lines. I will discuss how these results impact the interpretation of CO(2-1) studies at high and low redshifts, and motivate the need for resolved, multi-CO line surveys of larger samples of galaxies.

Forming stars and their planetary systems: a tale of dust, gas and magnetic fields

Special Colloquium
Dr. Anaëlle Maury
ORATED
CEA-Saclay and Harvard-Smithsonian CfA

Wherever we have the means of observing them, magnetic fields are detected across the full spectrum of astrophysical environments, from our own Earth, to stars, and cosmological structures. Magnetic fields are also present at all scales and evolutionary stages of star-forming structures. They have long been suspected to play a key role in shaping the typical outcome of the star formation process, such as stellar mass, spin, and multiplicity, or even the fate of stars towards their ultimate stages. In this talk, I will provide a global outlook on the progresses made in the recent years to characterize the role of magnetic fields during the embedded phases of the star formation process. Thanks to the development of observational capabilities and the parallel progress in numerical models capturing most of the important physics at work during star formation, we have successfully confronted detailed predictions of magnetized models to observational properties of the youngest protostars. I will present the physical processes and observational methods allowing to trace the magnetic field topology and its intensity in embedded protostars, and review the main steps, success and limitations in comparing real observations to synthetic observations from the non-ideal MHD models. I will describe in more details the physical conditions required to ensure an efficient magnetic field coupling, and present our work characterizing the two main agents responsible for the coupling in star-forming cores: dust grains and ionized gas. Following this Ariane thread, I will argue our observational and theoretical findings support a novel scenario where the magnetic field and the evolution of dust grains around solar-type protostars are tightly linked. Putting them in the broader context of protoplanetary disk studies, I will show how these findings deeply modify our paradigm of planet formation, ultimately shedding light on the formation and properties of exoplanetary systems, a fascinating question which has been at the heart of our quest to define mankind and the conditions for life to develop in a broader context. I will conclude by describing promising avenues to further explore the properties of young stars and the planets forming around them, their magnetic fields and dust pristine properties, getting the best fruition from future developments of both observational and computational capabilities.

Revealing the star formation history of our solar neighborhood

Main Colloquium
Dr. Catherine Zucker
ORATED
Space Telescope Science Institute, Baltimore, Maryland, USA

Given its proximity, the solar neighborhood has long been considered a fundamental laboratory for understanding how stars form. However, until very recently, this understanding was largely based on static ''plane of the sky'' views, making it extraordinarily challenging to build a 3D physical picture of gas and young stars using 2D integrated quantities. In this talk, I will discuss how new 3D spatial and dynamical constraints from Gaia, in combination with new data science and visualization techniques, have transformed our understanding of star formation near the Sun. In particular, I will show how ''3D dust mapping'' has provided never-before-seen 3D spatial views of the interstellar medium: redefining the structure of the Local Arm of the Milky Way, giving rise to previously undiscovered superbubbles, and constraining the detailed morphologies of individual molecular clouds at 1 pc resolution. Combining 3D dust mapping with the 3D space motions of young stars, I will show how we can reconstruct the star formation history of the solar neighborhood over the past 20 Myr, and in doing so, explain the origin of all nearby star formation as being driven by the expansion of the Local Bubble. I will conclude by discussing new opportunities with Gaia DR3, as well as the implications of our results for the theory and simulation communities.

A LAsMA survey of the Milky Way: Effects of feedback on molecular clouds

Promotionskolloquium
Parichay Mazumdar
ORATED
MPIfR

Molecular Cloud (MC) surveys play a crucial role in helping us understand their structure and composition. In addition, they are also essential in understanding the theory of star formation and testing various models of the Milky Way. During this thesis defense, I will present the work done on starting a new large-scale high-resolution survey (LAsMAGal) of giant molecular clouds (GMCs) in the Milky Way. The proposed survey is a first of its kind which simultaneously covers both 12CO and 13CO (3-2) lines. It also has a higher angular resolution and sensitivity than previous surveys of the southern Milky Way. I will first motivate the need for a new survey and present the results of the pathfinder study conducted to kick start the survey and test the feasibility of various observing strategies. Following this, I will demonstrate the capabilities of the new survey by presenting the observations taken towards the G305 star-forming GMC to study the effects of stellar feedback on the GMC. LAsMAGal data in combination with other ancillary survey data were used to investigate how the feedback from the central cluster of OB stars in G305 impact three separate aspects of the GMC, namely gas excitation, dynamics, and star-forming ability. I will conclude by briefly stating the current status of the survey and other science being carried out using LAsMAGal data. [Referees: Prof. Dr. Karl M. Menten , Prof. Dr. Pavel Kroupa, Prof. Dr. Klaus Desch, Prof. Dr. Matthias B. Hullin]

From cosmic web to molecular clouds: the multiple scales of galaxy evolution

Special Colloquium
Prof. Amélie Saintonge
ORATED
University College London, UK

Galaxy evolution is regulated by gas accretion from the intergalactic medium, the cooling and processing of this material into stars in the interstellar medium, and the return of some of the gas and metals to the circumgalactic environment via feedback processes. This framework is built upon an extensive network of observed scaling relations between galaxy physical properties, many of which are crucially measured through large dedicated surveys at submm/mm wavelengths with facilities such as IRAM, JCMT, APEX and ALMA. In this talk, I will review key results from such studies of the cold ISM of nearby galaxies, with a particular emphasis on the systematic variations in star formation efficiency and ISM physical properties, and the lessons they teach us about galactic-scale processes such as star formation, dust production/destruction, mixing and gas transport. I will also argue that much needed breakthroughs in our understanding of star formation and galaxy evolution will come from the next generation of (sub)mm facilities, which will allow us to connect the cold ISM of large samples of galaxies with the environment that feeds them (the circumgalactic medium, in particular), and to quantify the impact of the galactic environment on the star-formation process on molecular cloud scales, both at low and high redshifts, as a stepping stone towards a universal theory of star formation.

Cold chemistry in hot cores: new modeling treatments of complex molecule formation in star-forming regions

Main Colloquium
Prof. Robin Garrod
ORATED
University of Virginia

Reactions on dust-grain surfaces are responsible for the production of many important interstellar molecules, including gas-phase H2, grain-surface ice species such as water, ammonia and methanol, and arguably some of the most complex molecules detected in star-forming regions. However, our view of the temperature dependence of this chemistry has recently been changing. A major driver in this shift is the gas-phase detection of complex organic molecules (COMs) such as methyl formate in cold pre-stellar cores. These detections have pushed back the astronomical clock on COM production, to a time much earlier than the warm proto-stellar stage in which they are usually detected (albeit in much greater abundance). Experimental evidence also suggests that COMs may be formed on very cold surfaces (~10 K), through mechanisms that do not require thermal diffusion of the reactants. Past models that rely solely on diffusive reaction mechanisms now appear inadequate. I will discuss new modeling treatments that adopt a more comprehensive framework for grain-surface and ice-mantle chemistry, allowing reactants to meet in a variety of ways that do not rely solely on diffusion. This allows COMs to form as the ice mantles grow, while processing of the ices by external and cosmic-ray-induced UV fields can also lead to COM production. The period when the water-dominated ices desorb from the grains also allows trapped radicals to meet and react on the warm ice surfaces, prior to desorption. Gas-phase chemistry can further enhance COM production in some cases. In combination, these processes allow COMs to form over a range of temperatures, through a variety of mechanisms. I will discuss the implications of this new picture of COM chemistry on the origins and abundances of both familiar and more unusual COMs in star-forming regions.

New insights in Galactic magnetism from the THOR survey

Special Colloquium
Prof. Jeroen Stil
ORATED
University of Calgary, Canada

The HI/OH/Recombination line (THOR) survey includes the first broad-band (1 - 2 GHz) spectro-polarimetric continuum survey of the inner Milky Way. This allows polarimetry and measurements of Faraday rotation for Galactic and extragalactic sources over a large section of the first Galactic quadrant. After a brief introduction of THOR, I will introduce how broad-band polarimetry enhances Faraday rotation as a probe of Galactic magnetism, illustrated by three results from the THOR polarization survey. First, I will present a new view of Faraday rotation associated with the Milky Way's large-scale magnetic field in the first quadrant. Second, THOR's broad-band polarimetry of supernova remnants reveals their internal Faraday rotation. The third example addresses magnetic field structure on sub-parsec scales by differential Faraday rotation across extragalactic sources behind the Milky Way. These examples serve to show the rich data that modern spectro-polarimetric surveys like THOR have to offer.

Titans of the Early Universe: The birth of the first supermassive black holes

Main Colloquium
Dr. Tyrone Woods
ORATED
NRC Herzberg Astronomy and Astrophysics Research Centre, Victoria, Canada

The discovery of billion-solar-mass quasars at redshift ~ 7 challenges our understanding of the early Universe — how did such massive objects form in the first billion years, and what can this tell us about their environments at Cosmic Dawn? Observations and theory increasingly favour a "heavy seed" or "direct collapse" scenario, in which the rapid accretion possible in some primordial halos leads to the formation of uniquely supermassive stars, which collapse to form the initial seeds of supermassive black holes. In this talk, I'll present systematic, self-consistent simulations of the evolution of these objects under realistic formation conditions, and propose observational diagnostics to decisively test the origin of high-z quasars using next generation electromagnetic and gravitational wave observations. I'll also discuss the expected multiplicity of such supermassive stars and their subsequent interactions, as well as the unique observational signatures of primordial stellar populations which are intermediate in mass between supermassive objects and "typical" Pop III stars detectable by JWST and next generation observatories in the coming years.

Star formation relations in molecular clouds

Special Colloquium
Dr. Riwaj Pokhrel
ORATED
Department of Physics and Astronomy, University of Toledo, USA

One of the well-established empirical results in astronomy is the Kennicutt–Schmidt relation between the surface density of interstellar gas and the rate at which the gas forms stars. A tight correlation between these quantities has long been measured at galactic scales. However, until recently the correlations on molecular cloud scales are found to vary between individual clouds. Through the Spitzer Extended Solar Neighborhood Archive (SESNA) and a matching Herschel archival effort, we have compiled huge, uniform maps of the structure of young star distributions and molecular gas for twelve nearby (<1.5 kpc) molecular clouds. In this talk, I will present a comprehensive analysis of the relation between star formation rate density and mass surface density of molecular gas over a wide range of sampling scales based on SESNA and Herschel observations. The ``universal” star formation relations in the star-forming clouds in the solar neighborhood will be discussed. I will also provide a brief update on other recent progress on observed star formation relations and simulation efforts and challenges in trying to explain the observed star-gas correlations.

A comprehensive study of NGC5195: physics, chemistry, morphology and effects of the galaxy interaction in its interstellar medium

Master Colloquium
Reem Aboelsoud
ORATED
Max-Planck-Institut für Radioastronomie

Studying the chemical composition of the molecular clouds in the central regions of galaxies helps us to infer the type of the nuclear activity. NGC5195, or M51b, is an iconic example of a nearby galaxy that had a recent interaction with its companion, M51, 50-500 Myr ago. In this thesis, we used NOEMA data to study the nucleus of NGC5195, its nuclear activity, and the effects of the interaction on its ISM. High resolution observations of CO(1-0), CN(1-0), HCN(1-0), HCO+(1-0) and HNC(1-0) towards the galaxy (2'' ~ 100 pc) were performed. Comparison between the spectra at the position of the nuclear source and the whole mapped area enabled us to investigate the nature of NGC5195 central activity. We conclude that an active AGN is likely not powering the galaxy. In addition to the moment maps of all lines, which show the intensity distribution, velocity fields and velocity dispersion, we also studied the intensity integrated ratio maps among CO/CN, HCN/CN, HCN/HCO+, CO/HCN, and HCN/HNC. The most interesting ratios were CO/HCN and CO/CN. Those two ratios show that M51b has two twin peaks in the East-West direction of the center. These peaks are oriented nearly perpendicular to the large scale bar and connected to a curved structure. The nucleus of M51b is surrounded by concentrations of dust, making a ring shape, and we found that the radius of the dusty ring is spatially coincident with the two molecular peaks found in our work. We have also studied how the source of the nuclear activity could affect the values of some molecular ratios. To make this comparison, we chose our galaxy observation, M51b, and 8 other galaxies, including starburst galaxies (M83, NGC 253 and M82), galaxies hosting AGNs (NGC 1068, NGC 7469 and M51), ULIRGs (Arp 220 and Mrk 231). What differentiates NGC5195, in comparison to the rest of the galaxies, is its post-starburst phase after its interaction with M51, which is characterised by a large amount of diffused gas, resulting in a high CO/HCN ratio. [Referees: Prof. Dr. Karl Menten, Prof. Dr. Frank Bigiel]

The molecular torus of NGC1068

Main Colloquium
Dr. Violette Impellizzeri
ORATED
Leiden Observatory, The Netherlands

Active galactic nuclei (AGN) play an important role in the shaping and evolution of galaxies. However, understanding their properties has been challenging due to the extraordinary sensitivity and resolutions required to study them. Such detailed observations are finally becoming accessible thanks to ALMA, VLTI and high sensitivity VLBI observations. In this talk, I will present results of the prototypical Seyfert 2 nucleus in NGC 1068. We have now obtained data with a factor 2 better resolution (1 pc-scale) with the most extended ALMA configurations, revealing clear indications of an outflow originating from the nucleus (consistent with the outflow observed in CO), and the presence of two nested, rotating disk components. The inner disk, inside 1.5 pc, has kinematics consistent with the edge-on, geometrically thin H2O water megamaser disk. The outer disk, which extends to 7 pc, is also geometrically thin but inclined. The outer disk counter-rotates relative to the inner, water megamaser disk. I will conclude with a picture in which the torus consists of two geometrically thin, counter-rotating disks, and the nuclear obscuration occurs in outflowing molecular clouds whose origin is likely a hydromagnetic wind driven off of the inner disk. I will also present new, sensitive VLBI observations of the water megamasers releasing for the first time the existence of linear substructures, or ''spokes,'' among the maser spots that suggest the influence of magnetic fields. The position-velocity diagram shows curvature consistent with elliptical orbits or spiral arm structure within the megamaser disk. We find that a warped-disk model fits the data well, and the de-projected model reveals candidate spiral arm structures. Finally, we were able to recover the 22 GHz continuum on short baselines. The resulting continuum image shows a distorted X-shaped morphology, which we can match with VLTI observations, changing our picture of the inner core dramatically. One arm of the X aligns with the m aser disk, suggesting that the continuum arises in an edge-on plasma disk. The other arm orients more nearly perpendicular to the maser disk, resembling sub-parsec lobes in an ionized outflow or jet.

Recent update on the front-end system of VERA - Ultra-wide band polarimetry

Informal Colloquium
Prof. Dr. Yoshiaki Hagiwara
ORATED
Toyo University, Japan, ASTRON/JIVE Visiting Scientist

*** Warning: room changed, now it is the library seminar room 2.05*** The most recent front-end developments for 4 x 20m radio telescopes of VLBI Exploration of Radio Astrometry (VERA) will be reported. We will show a brief overview of currently ongoing technical developments of a dual circular polarization receiving and ultra-wide band (16 Gbps) recording systems that have been installed to each of the 4 telescopes of VERA. With these developments for the wide band VLBI polarimetry, it is now possible to study magnetic field properties of radio jets in active galactic nuclei, masers in star-forming sites, and stellar envelopes in late-type stars at unprecedented sensitivity. The observing performance obtained from most recent performance test observations will be also presented.

Blazar Multiwavelength Variability and VLBI Connection

Special Colloquium
Dr. Víctor Patiño-Álvarez
ORATED
MPIfR-INAOE Partner Group Leader, Instituto Nacional de Astrofísica, Óptica y Electrónica, Puebla, Mexico

I will present some of the results obtained during the last three years by myself and the INAOE AGN Group, including the work of the Master and PhD students. Among the multiwavelength variability studies I will mention the results of different papers on the sources 3C 273, CTA 102, 3C 454.3, B2 1633+382, and PKS 1510-089. I will talk about the correlations obtained between the variability at pc-scales and the gamma-ray variability, for the sources 3C 279 and 3C 454.3; this with the objective of directly locating gamma-ray emission regions on the VLBA maps (and we succeeded). Lastly I will briefly talk about the Baldwin Effect, which is a relationship between spectral characteristics of AGN, that despite being studied for over four decades, there was no consensus on the driving mechanism of said relationship. However, we present observational evidence that probes that the Baldwin Effect is a direct and natural consequence of the relationship between the ionizing continuum and the emission line luminosities.

Recent imaging adventures with MeerKAT

Main Colloquium
Dr. Ian Heywood
ORATED
University of Oxford, UK

The South African MeerKAT telescope recently marked four years since inauguration, and three years of scientific observing in pursuit of its large survey programs and open time projects. I will present results from three imaging projects that I have been involved in, covering extragalactic deep fields from the MIGHTEE survey, a study of an unusual pulsar that was a joint venture between MeerTRAP and ThunderKAT, and an update on the observatory-led Galactic centre survey. I will discuss some of the data processing advances and challenges that have resulted from this work.

Interstellar scintillation and polarization of PSR J0538+2817 and PSR B0659+1414

Main Colloquium
Dr. Jumei Yao
ORATED
National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China

SNR shells have long been suspected as the culprits for dominating pulsar scattering. The interstellar scintillation observation of pulsars associated with SNRs provide us with great opportunity to find evidence for this and reveal the properties of the compact ionized structures. Using FAST, we did high sensitivity interstellar scintillation and polarization observations of PSR J0538+2817 and PSR J0659+1414. For PSR J0538+2817, we found that the shell of SNR S147 dominates its scattering and detected the first evidence for pulsar three-dimensional spin-velocity alignment. The scattering of PSR J0659+1414 is dominated by two different compact regions, the shell of the Monogem ring and the Local Bubble. And the polarization analysis shows that the spin and velocity vectors of PSR J0659+1414 are significantly misaligned.

The physical and chemical condition of Thackeray 1

Master Colloquium
Shampa Bhusal
ORATED
Max-Planck-Institut für Radioastronomie

Globules, associated with H II regions, are one of the best laboratories to study the impact of stellar radiation and feedback from expanding H II regions on the surrounding medium. First detected by A. D. Thackeray (1950) in the southern H II region IC 2944, the so-called Thackeray’s globules are prime examples of such objects. In this thesis, I present APEX telescope observations of the largest globule in the complex, Thackeray 1, in low level rotational transition of CO and [CI], together with an unbiased spectral line survey in the 230 GHz atmospheric window. I have used this data to probe the physical and chemical conditions of the molecular gas and the photo dissociation regions (PDR) in Thackeray 1. The velocity resolved CO observations suggest that the largest globule is the overlap of two separate regions with masses ~ 11 Msun and 3 Msun corresponding to Thackeray 1A and Thackeray 1B, whereas the continuum dust emission with LABOCA 870 mum reveals an overall mass of ~ 19 Msun . The two regions are kinematically separated with velocities of -20 and -25 km s-1. The line survey reveals for the first time an unbiased view on the chemical molecular composition of these globules, with new detection of molecules such as C18O (2–1), H2CO(3 0,3 – 2 0,2 ), SO, HCN, HNC, HCO+, C2H and CS. MCweeds is used to constrain the column densities and abundances of these species. The incident FUV field intensity, G0 and hydrogen nucleus volume density n are estimated by using PDRTool box models constrained by observed CO line ratios. The data allows to investigate the stability of the globule by estimating their virial mass and ionization timescale. Both parameters confirm previous studies, including the HST image result, that the globule complex, Thackeray 1 is on the verge of breaking up or evaporating. [Referees: Prof. Dr. Karl Menten, Prof. Dr. Frank Bigiel]

Our Galaxy’s Center: a Window into the High-Redshift Universe

Main Colloquium
Prof. Cara Battersby
ORATED
University of Connecticut

Galaxy centers are the hubs of activity that drive galaxy evolution, from supermassive black holes to dense stellar clusters and feedback from newly-formed stars. Our own galaxy’s center has properties (densities, temperatures, and turbulent line widths) that are reminiscent of galaxies at the peak of cosmic star formation, but in our own cosmic backyard, where the interplay of these physical processes can be resolved in detail. In this talk, I will discuss gas inflow into our Galaxy’s Center, properties of the gas, and incipient star formation. I will discuss simulations of gas flows into the Galactic Center, which are thought to contribute to the unusual properties of star formation in this region, namely that it is producing 10 times fewer stars than predicted by standard scaling relations. I will describe observations of the gas and incipient star formation in this region, as well as discuss efforts to measure whether or not this unusual environment results in a change to the Initial Mass Function.

The next generation Very Large Array (ngVLA) - Science and Telescope Design

Special Colloquium
Dr. Bryan Butler
ORATED
NRAO, Socorro, New Mexico, USA

Building on the remarkable success of the VLA, VLBA, and ALMA, NRAO is planning a large collecting area interferometer which will replace the VLA and VLBA - the next generation Very Large Array (ngVLA). For many of the same reasons that the VLA was constructed where it was (fraction of sky visible, quality of site, accessibility, etc.), the core and bulk of the collecting area of the ngVLA will be on the Plains of San Agustin, near where the center of the current VLA is. The ngVLA will have more than 10 times the sensitivity and spatial resolution of the VLA and ALMA, operating at frequencies from 1.2-116 GHz. The ngVLA will be optimized for observations at wavelengths between those of ALMA at mm-submm wavelengths, and the future SKA-1 at dm-m wavelengths, to be complementary to those instruments. The ngVLA will be transformative, with exquisite sensitivity to thermal line and continuum emission down to milliarcsecond resolution. The science goals are broad (a science book with more than 90 chapters and 285 unique authors has been written), but focus on: formation of planetary systems on terrestrial planet scales, including astrochemistry; characterization of galaxy structure and evolution; using pulsars in the Galactic center to test fundamental theories of gravity; and understanding the formation and evolution of stellar and supermassive black holes in the era of multi-messenger astronomy.

Interstellar water isotopologues in high-mass star-forming regions

Master Colloquium
Mahathi Chavali
ORATED
Max-Planck-Institut für Radioastronomie

Water is a key molecule to model the physics and chemistry of star formation. It is also the main constituent of icy grain mantles in the universe. We studied HDO and H2O transitions observed by the APEX telescope in the ATLASGAL TOP100 sample containing 110 clumps representing all evolutionary stages of high-mass star formation. We studied the ratio of HDO/H2O as the level of deuterium fractionation of a molecule is a good tracer of its formation process. H2-18O, an isotopologue of water is observed as a tracer for water, as water is difficult to observe from the ground. Water deuterium fractionation has been studied before, but not in such a large sample and range of evolutionary stages. The analysis is complicated by line blending with transitions from other molecules. We analysed these observations using the 1D radiative transfer code RATRAN to obtain the fractional abundances of HDO and H2O. Our studies show that the water deuterium fractionation values are about two orders of magnitude larger in star forming regions, compared to the elemental D/H ratio. [Referees: Prof. Dr. Karl Menten, Prof. Dr. Frank Bigiel]

Our First Cloud-Scale Survey of Molecular Gas in Galaxies

Special Colloquium
Prof. Adam Leroy
ORATED
Ohio State University, USA

I will present PHANGS-ALMA a multi-cycle ALMA survey of 90 nearby galaxies that offered our first real cloud-scale survey of molecular gas in galaxies. Stars form in giant molecular clouds, which are dense, cold condensations of gas that in many ways act as the engines of galaxy evolution. The demographics, evolution, and physical state of these clouds relate directly to how star formation proceeds, feedback operates, and galaxies grow. Until recently, however, we lacked any large survey that resolved the gas in galaxies into individual clouds. Leveraging ALMA's amazing combination of resolution, sensitivity, and mapping speed, PHANGS-ALMA mapped the CO 2-1 emission, our basic tracer of molecular gas in galaxies, at 1" = 50-150 pc resolution scales across essentially all accessible very nearby star-forming galaxies. On its own, PHANGS-ALMA resolves the molecular gas across whole galaxies into individual star-forming molecular clouds, giving access to the demographics and properties of tens of thousands of molecular clouds across a representative set of z=0 galaxies. When paired with large programs on VLT/MUSE, HST, ALMA mapping of high critical density lines, and soon JWST and MeerKAT, PHANGS offers a pan-chromatic view that breaks a representative sample of galaxies into individual star forming regions for the first time. I will give an overview of the motivation and execution of the survey, describe the data and products available to the community, and then highlight results on a few key topics - demographics, life cycles, and star formation properties of clouds - from the PHANGS team.

Illuminating the magnetised cosmic web

Main Colloquium
Dr. Shane O'Sullivan
ORATED
Dublin City University

Radio galaxies can be observed throughout the majority of the history of the Universe and are thus excellent beacons for measuring the properties of the cosmic web and their evolution with cosmic time. Here I will highlight recent results from the ongoing LOFAR Two-metre Sky Survey (LoTSS), with a focus on the linear polarization and Faraday rotation measure (RM) data. The exceptional RM precision of LoTSS (< 0.1 rad/m2), in addition to unrivalled ancillary information such as the host galaxy redshift, has facilitated several new discoveries. For example, our recent detection of the RM signature from cosmic web filaments shows how LoTSS is transforming our understanding of cosmic magnetic fields, and providing a new way to study the properties of filaments and voids of the cosmic web in general.

Event Horizon Telescope: the shadow of the black hole in the center of the Milky Way

Special Colloquium
Various Panelists
ORATED
Event Horizon Telescope Collaboration

The Event Horizon Telescope (EHT) presented on May 12, 2022 the results from the observations of Sagittarius A* (Sgr A* ), the Galactic center source associated with a supermassive black hole. Those are based on observations conducted in 2017 with very-long-baseline interferometry operating at a wavelength of 1.3 mm. These results support an image dominated by a bright, thick ring with a diameter of about 52 microarcseconds, consistent with the appearance of a Kerr black hole with mass of 4 million solar masses. These results provide direct evidence for the presence of a supermassive black hole at the centre of the Milky Way. Details on these results will be provided in a series of short talks by MPIfR affiliated astronomers who are part of the EHT team, spanning over two hours including discussion: introduction by Anton Zensus and Karl Menten; followed by short presentations by Alan Roy, Michael Janssen, Eduardo Ros, Gunther Witzel, Christian M. Fromm, and Michael Kramer, concluding with a final discussion.

Relics of the ancient Universe: old ultra-compact massive galaxies as local laboratories to study the first phases of galaxy formation

Special Colloquium
Dr. Chiara Spiniello
ORATED
University of Oxford (UK)

Massive early-type galaxies (ETGs) are believed to form through a two-phase process: an intense and fast star formation episode creates red, compact, and massive objects (“red nuggets”), and then a second phase, dominated by mergers and gas inflows, causes structural evolution and size growth. Luckily, since merging is believed to be stochastic, a small fraction of red nuggets survives intact until the present-day Universe, without experiencing any further interaction: the so-called Relic Galaxies. These very old Ultra Compact Massive Galaxies (UCMGs) are made of “in situ only“ pristine stellar populations, and as such they provide a unique opportunity to track the formation of this specific galaxy stellar component, which is mixed with the accreted one in normal massive ETGs. In this talk I will first introduce our effort in obtaining a complete census of UCMGs at z between 0.1 and 0.5 from the Kilo Degree Survey, and then introduce the on-going INvestigating Stellar Population In RElics (INSPIRE) project which aims at building the first statistically large sample of confirmed relics. I will give few details on the target selection, observation, data analysis, strategies and results obtained in the INSPIRE Data Release 1, based on 19 systems for which observations were completed in 2020. In particular, I will present the kinematics and stellar population results and the relic confirmation for the biggest sample of spectroscopically confirmed relic galaxies currently available beyond the local universe. I will finally introduce some future perspectives and goals of INSPIRE, highlighting how relics can be used as powerful tools to study the early phases of massive galaxies formation.

Das erste Bild des Schwarzen Lochs im Zentrum der Milchstraße

Special Colloquium
PD Dr. Silke Britzen
ORATED
MPIfR

Die Event-Horizon-Teleskop- (EHT) Kollaboration hat am 12. Mai das erste Bild vom Schatten des Schwarzen Lochs im Zentrum unserer Galaxie veröffentlicht. Es ist das erste Bild von Sgr A* , aber bereits das zweite Bild eines supermassereichen Schwarzen Lochs (nach M87* ). Mit einem Netzwerk von acht Radioteleskopen, das fast die Größe der Erde erreicht, gelang ein Bild, an dem auch viele Kollegen aus dem MPIfR lange gearbeitet haben. Ich berichte über die Entstehung dieses Bildes, die Unterschiede zwischen Sgr A* und M87* und die Bedeutung der Aufnahmen für die Erforschung dieser kosmischen Schwerkraftfallen. [Dieser Vortrag richtet sich an alle Mitarbeiter des Instituts]

Stellar Tidal Streams around nearby galaxies in the local Universe

Special Colloquium
Dr. David Martı́nez Delgado
ORATED
Instituto de Astrofı́sica de Andalucı́a (CSIC), Spain

Within the hierarchical framework for galaxy formation, merging and tidal interactions are expected to shape large galaxies up to the present day. While major mergers are quite rare at present, minor mergers and satellite disruptions - that result in stellar streams - should be common, and are indeed seen in the stellar halos of the Milky Way and the Andromeda galaxy. In the last years, the Stellar Stream Legacy Survey (PI. Martinez-Delgado) has exploited available deep imaging of some nearby spiral galaxies with the ultimate aim of estimating the frequency, morphology and stellar luminosity/mass distribution of these structures in the local Universe. In this talk, I will present the current results of our systematic survey of stellar streams together with some recent follow-up observations (e.g. Megara, Subaru) and N-body modelling of the most striking streams. Finally, I will discuss what we can learn about galaxy formation from the results of this survey, including the comparison with the available L-CDM cosmological simulations.

High-precision laser spectroscopy meets astronomy

Main Colloquium
Prof. Simon Stellmer
ORATED
Physikalisches Institut der Universität Bonn

Astronomy and low-energy quantum physics experiments might seem to be located at opposite ends of the spectrum of physics research, but there are surprisingly many connections. I will elaborate on two of such topics. Firstly, I will present searches for beyond-standard-model physics based on precision spectroscopy. Secondly, I will advertise a new initiative to determine the Earth orientation parameters through a novel type of ring laser gyroscope.

Out-of-focus holography at the Effelsberg telescope

Special Colloquium
Dr. Tomás Cassanelli
ORATED
Departamento Ingeniería Eléctrica, Universidad de Chile, Santiago, Chile

The sensitivity of a radio telescope is of significant scientific interest. By increasing the sensitivity (or increasing the aperture efficiency) we are able to reduce errors in the telescope's main beam, and hence detect fainter sources. Out-of-focus (OOF) holography is a method to determine errors in the aperture plane of a radio telescope. In contrast to traditional holography, OOF can be applied without extra equipment and using common astronomical sources and receivers. By correcting aperture errors we are improving the surface accuracy, and effectively improving the aperture efficiency. In this talk I will describe the method, the developed software (pyoof), the observations, and how it is applied to the Effelsberg telescope. Results from multi-year observational campaigns will also be discussed, in an effort to model repeatable sources of deformation over the 100-m collector and improve its surface efficiency.

The PAH revolution: cold, dark carbon at the earliest stages of star formation

SFB Colloquium
Prof. Brett McGuire
ORATED
Massachusetts Institute of Technology, Cambridge, USA

Polycyclic Aromatic Hydrocarbons (PAHs) have been implicated as a large reservoir of reactive carbon in the interstellar medium since the 1980s. PAHs have been widely attributed as the carriers of the unidentified infrared bands where their aggregate vibrational emission spectra are extremely well matched to the observed line signals. Only in the last year have individual PAHs been detected in the ISM for the first time, however, allowing us to begin to investigate the detailed chemical pathways for the formation and destruction of these molecules. In this talk, I will discuss our detections of PAH molecules via their rotational transitions using Green Bank Telescope observations of TMC-1 from the GOTHAM collaboration. I will discuss the efforts to model the chemistry of these PAHs, the necessity of complementary laboratory kinetics work, our application of novel machine learning approaches to exploring the chemical inventory in TMC-1, and finally the benefits of unbiased reaction screening studies in the laboratory with Microwave Spectral Taxonomy.

Astrochemical approach to understand star and planet formation

Main Colloquium
Dr. Nami Sakai
ORATED
RIKEN Cluster for Pioneering Research, Saitama, Japan

Star and planet formation is one of the most fundamental structure-formation processes in the Universe. Physical processes of star and planet formation have widely been investigated as one of the major targets of astronomy and astrophysics by observations in all the wavelength region from radio to X-ray during the last few decades. Although a rough outline of these processes has been presented, there remain many unknowns and missing links. On the other hand, star and planet formation is a process where interstellar matter is evolved into planets. Hence exploring chemical evolution is of fundamental importance in understanding the origin of the Solar system, and eventually the origin of life on the Earth.  We have thus started to study the chemical evolution by collaborating with people in molecular science field. Such chemical approach also tells us novel information on physical processes of star and planet formation. In this talk, I will introduce efforts on such studies.

z-GAL: a comprehensive redshift survey of the brightest Herschel galaxies

Special Colloquium
Dr. Pierre Cox
ORATED
Institut d'Astrophysique de Paris, France

The Herschel surveys have enabled the detection of numerous dusty luminous sub-millimeter galaxies (SMGs) in the early universe. Follow-up observations of these sources are essential to determine their nature and the physical properties of their interstellar medium; reliable measurements of their redshifts are therefore crucial to explore the molecular and atomic gas of these objects. I will here present the results of a Large Program, z-GAL, using NOEMA, aimed at a comprehensive 3 and 2-mm spectroscopic redshift survey of a large (~140 sources) sample of the brightest (S500microm>80 mJy) SMGs selected from the Herschel H-ATLAS and HerMES surveys, which probe the peak of cosmic evolution (2

From galaxy-scale feedback through cosmic history to the microwave background temperature evolution: an updated view on the early Universe from new tools in (sub)mm astronomy

Main Colloquium
Prof. Dominik Riechers
ORATED
Universität zu Köln

Recent years have seen great advances in studies of galaxy evolution and the early Universe due to substantial upgrades in our observational capabilities, coupled with ever more complex simulations of star, galaxy, and cosmic structure formation. I will highlight a range of new investigations of the cosmic baryon cycle coupling galaxies to their environments through their gas reservoirs, gas accretion, and outflows as a result of feedback processes driven by newly formed massive stars and active galactic nuclei. These properties evolve through cosmic history due to changes in the properties of "typical" galaxies and those undergoing their most intense phases of activity, but also due to changes in the environments resulting from the formation ever more pronounced cosmic structures and the cooling of the Universe due to cosmic expansion. I will introduce a new method to constrain the latter through direct line absorption against the cosmic microwave background, and promising new observational methods to constrain the former through large-scale line intensity mapping surveys of the early Universe, all the way back to cosmic reionization. Due to the rapid progress in observational, theoretical, and laboratory astronomy over the past decade, as well as new trends in astronomical instrumentation and facilities like CCAT-prime, ALMA 2030, NOEMA, the SKA and the ngVLA, we will have the tools to usher in a new phase in our understanding of the evolving cosmos back to its infancy stages in the coming decade.

Search for MIlli-LEnses (SMILE) to discriminate between dark matter models

Special Colloquium
Dr. Carolina Casadio
ORATED
Institute of Astrophysics - FORTH, Heraklion, Greece

Projects aimed at characterising dark matter properties make use of very different approaches. One such approach is to look for strong gravitational lens systems. Gravitational lensed images with angular separation on milli-arcsecond scales probe gravitational lens systems where the lens is a compact object with mass in the range 10^6-10^9 solar masses, i.e. a supermassive compact object (SMCO). This mass range is particularly critical for the widely accepted cosmological model, which predicts many more DM halos on sub-galactic scales (< ~ 10^11 solar masses) than currently observed. The most direct way to explore these small angular scales is through the high-resolution of radio Very Long Baseline Interferometry (VLBI). We perform a pilot search, using the Astrogeo VLBI FITS image database and collecting multi-frequency, multi-epoch VLBI data of 13828 individual sources. We identified 40 milli-lens candidates, which have been followed-up with multi-frequency European VLBI Network (EVN) observations. Performing a similar search in a complete sample of ~ 5000 sources would allow us to constraint the abundance of SMCO in the Universe with more than an order of magnitude better precision than in previous studies, and to ultimately reject many currently viable DM models.

VLBI, multi-band and multi-messenger studies of AGN

Special Colloquium
Prof. Dr. Yuri Y. Kovalev
ORATED
Astro Space Center of Lebedev Phys. Inst. and Moscow Inst. of Phys. and Technology, Moscow, Russia

In this talk I will discuss recent developments in AGN studies on parsec and sub-parsec scales made with ground and Space VLBI as well with multi-band and multi-messenger observations. These include the extreme brightness temperature puzzle of RadioAstron measurements, the VLBI-Gaia view on the AGN disk-jet system, and the mounting observational indications for the blazar-neutrino connection. I will conclude the talk by outlining several exciting opportunities for centimeter and millimeter single-dish and VLBI experiments which will be playing a key role in the coming new era of multi-messenger astronomy.

First light for CONCERTO at APEX!

Main Colloquium
Dr. Guilaine Lagache
ORATED
Laboratoire d'Astrophysique de Marseille, Frankreich

CONCERTO is a new instrument that has just been successfully installed in the Cassegrain Cabin of the APEX telescope. It is a spectrometer with an instantaneous field of view exceeding 260 square arcminute and a spectral resolution up to 1.5 GHz. It covers the frequency band 130-310 GHz. The main scientific aim of CONCERTO is to map in 3D the fluctuations of the [CII] line intensity in the reionisation and post-reionisation epoch (z>5). This technique, known as intensity mapping, will allow us to address questions about the contribution of the dust-enshrouded star formation at z > 5, the history of metal enrichment, and the role of star-forming galaxies in shaping cosmic reionization. In addition to the main [CII] survey, we expect CONCERTO to bring a significant contribution in a number of areas, including the study of galaxy clusters (via the thermal and kinetic SZ effect), the follow-up of cosmological deep surveys, the observation of local galaxies, and the study of Galactic star-forming clouds. CONCERTO will also observe the CO intensity fluctuations arising from 0.3

The Galactic chemical evolution of heavy elements

Main Colloquium
Dr. Eda Gjergo
ORATED
Wuhan University, China

The astrophysical sites which dominate the production of r-process elements have been a matter of contention for decades. The event GW170817/AT2017gfo, with the confirmed observation of the neutron-capture element strontium, originally raised hopes that neutron star mergers (NSM) could be a leading contributor to the production of heavy elements. However, galactic chemical evolution (GCE) models which take into account the rates of NSM events show that the onset of NSM occurs too late in the enrichment history to explain the abundance patterns of extremely metal poor stars. Among the other candidates is the small fraction of core-collapse supernovae whose progenitor star rotates sufficiently fast and creates magneto-hydrodynamic jets (MHDJ) capable of yielding r-process enrichment. It is possible that the rarity of such events may be offset by the larger rates and mass ejecta. After an introduction on GCE modeling, I will present results which include novel yield tabulations of neutron-capture events. I will explore the dependence of neutron-capture element abundances on theoretical NSM rates, as well as on future GW missions. We investigate some variation of parameters in single-zone GCE models for both the Milky Way and dwarf galaxies. On a s-process production baseline by AGB and core-collapse SNe, we estimate which conditions favor one r-process enrichment scenario over the other.

Energy dissipation in extragalactic jets

Main Colloquium
Prof. Karl Mannheim
ORATED
Institut für Theoretische Physik und Astrophysik, Universität Würzburg

The plasma composition of jets ejected from accreting black holes in active galactic nuclei remains uncertain up to the present day. Inevitably, photon-photon pair production must lead to an excess of electron-positron pairs that remains unaccounted for in conventional single-fluid GRMHD simulations. Photon-photon pair production occurs in the virial plasma close to the ergosphere. Prolific pair production also results from particle acceleration throughout the jet. Multi-TeV gamma rays and the tentative associations of blazars with high-energy neutrinos and of radio galaxies with ultra-high energy cosmic rays require efficient acceleration of particles to ultra-high energies. Considerable efforts to encompass the kinetic processes responsible for the transport and acceleration of relativistic particles are currently undertaken to better understand how they shape the morphology and spectral energy distributions of jets. Studies of variability are key to understand the anisotropies associated with the acceleration processes and the stochastic nature of energy dissipation. Dissipation by kinetic processes resembles an exponential version of Ohmic dissipation in an electric wire.

TBD

Main Colloquium
Prof. Sara Buson
CANCELED
Institut für Theoretische Physik und Astrophysik, Universität Würzburg

TBD

Astrophysics of suprathermally rotating dust: from grain alignment and rotational disruption to surface chemistry

Main Colloquium
Prof. Thiem Hoang
ORATED
Korea Astronomy and Space Science Institute, Daejeon, Republic of Korea

Dust is ubiquitous in the Universe and plays an important role in astrophysics. Dust grains are the building blocks of planets and catalytic surfaces for the formation of water and complex molecules. Dust polarization induced by the alignment of dust grains with the magnetic field is a powerful technique to observe cosmic magnetic fields and constrain dust properties. Dust grain size distribution determines star extinction and is a fundamental property for describing radiation pressure feedback from stars, supernova, and active galactic nuclei. In this talk, I shall show that grain’s suprathermal rotation plays a crucial role in dust astrophysics, determining grain alignment and affecting grain size distribution and surface chemistry. I shall first review the main physical mechanisms for grain alignment, including radiative torques and mechanical torques. I will then discuss the physics of rotational disruption of dust grains due to radiative torques, which implies the change of the dust properties with the local radiation field and density from the local medium to high-redshift galaxies. I will also discuss the new effects of suprathermal rotation on surface chemistry, radiation pressure feedback, and grain growth. Finally, I shall discuss a synergy of synthetic modeling with observations to test the new dust physical effects, probe dust properties, and measure magnetic fields in star-forming regions.

Planets are places: characterization of other worlds in the 2020s and beyond

Main Colloquium
Dr. Laura Kreidberg
ORATED
Max-Planck-Institut für Astronomie, Heidelberg

The past 25 years have revealed a diversity of exoplanets far beyond what was imagined from the limited sample in the Solar System. With new and upcoming observing facilities and a rapidly growing number of nearby planets, we are poised to bring this diversity into focus, with detailed follow-up characterization of the planets’ atmospheres. In this talk, I will discuss two frontier topics in exoplanet atmosphere studies: (1) what can we learn about giant planets' origins from their present-day atmospheres? and (2) what can we learn about habitability from “Earth cousins”, planets that are a little bigger or a little hotter than the Earth? Finally, I will conclude with my outlook on the search for biosignatures in the atmospheres of potentially inhabited planets.

A NICER view of neutron stars

Main Colloquium
Prof. Anna Watts
ORATED
Astronomical Institute Anton Pannekoek, University of Amsterdam

NICER, the Neutron Star Interior Composition Explorer, is an X-ray telescope that was installed on the International Space Station in 2017. Its mission is to study the nature of the densest matter in the Universe, found in the cores of neutron stars. NICER uses Pulse Profile Modeling, a technique that exploits relativistic effects on X-rays emitted from the hot magnetic polar caps of millisecond pulsars. The technique also lets us map the hot emitting regions, which form as magnetospheric particles slam into the stellar surface. I will present NICER's latest results - including a measurement of the radius of the highest mass pulsar known - and discuss the implications for our understanding of ultradense matter, pulsar emission, and stellar magnetic fields. I will also look ahead to the next generation of X-ray telescopes that will exploit the Pulse Profile Modelling technique.

Enabling wide-field, high-spatial-resolution fast transient searches on modern interferometry

Promotionskolloquium
Weiwei Chen
ORATED
Max-Planck-Institut für Radioastronomie

Fast transients are usually the products of rapid and enormous energy releases. To study the physical nature behind them, we must know the subtle temporal structure of the signal and where precisely they come from. However, some sporadic or even one-off fast radio transients have brought challenges to the current instruments. In this presentation, I describe the general beamforming technique, withwhich efficient wide-field, high time and spatial resolution survey can be achieved. Following that, I introduce the software package: MOSAIC developed for this project to provide the solutions to the challenges that come with this technique, such as the characterization of volatile beam shapes, the generation of efficient tiling of beams and the prediction of the evolution of the tiling through time. As an evaluation, a beamformed observation with MeerKAT on 47 Tucanae using the said techniques is presented and the localization capability with multiple beams is demonstrated. The performance of this beamforming platform has been further tested in numerous observations and surveys such as TRAPUM and MGPS that have yield significant results. I also report a search for giant pulses in selected pulsars. Many models try to explain the emission mechanism behind giant pulses from pulsars, some of which invoke the re-connection events near the light cylinder. In the meantime, a population of known giant pulse emitters shares similar properties, such as strong magnetic fields near the light cylinder and high energy emission. I select a couple of pulsars with these properties as candidates and observed them using the Effelsberg 100-meter telescope. A pipeline based on Heimdall was created to search giant pulses on the data and no credible detection was found. The conclusion for the non-detection is that these pulsars do not emit giant pulses which are detectable by our observation, or the high magnetic field strength near the light cylinder may not be a sufficient condition for the occurrence of giant pulses. [Referees: Prof. Dr. Michael Kramer, Prof. Dr. Frank Bertoldi, Prof. Dr. Ian Brock, Prof. Dr. Klaus Greve]

Towards prebiotic chemistry in the interstellar medium

Main Colloquium
Dr. Izaskun Jiménez-Serra
ORATED
Centro de Astrobiología, Madrid, Spain

In the past decade, Astrochemistry has witnessed an impressive increase in the number of detections of complex organic molecules. Some of these species are of prebiotic interest such as glycolaldehyde, the simplest sugar, or amino acetonitrile, a possible precursor of glycine. Recently, we have reported the detection of several new complex organic species in the interstellar medium, such as hydroxylamine and ethanolamine, known to be intermediate species in the formation processes of ribonucleotides and phospholipids within theories for the origin of life. In this talk, I will present our recent efforts to establish whether key precursors of prebiotic systems chemistry can be found in space. I will also analyse how chemical complexity builds up in the interstellar medium thanks to observations of the complex organic content in starless/pre-stellar cores, which represent the initial conditions of Solar-system formation.

The cradles of star and planet formation: disks, multiplicity, and stellar masses of low to intermediate-mass protostars

Main Colloquium
Dr. John Tobin
ORATED
National Radio Astronomy Observatory, Charlottesville, USA

The formation of disks and multiple star systems are integral parts of the star and planet formation process. Most stellar mass must be accreted through a disk, disks are the future sites of planet formation, and disks will also give rise to companion stars. Using ALMA and the VLA, we are conducting large continuum surveys of protostars (with molecular lines toward a subset of the full sample) in the nearby Perseus and Orion star-forming regions (with 20-30 au resolution) to characterize the disk radii, disk masses, and frequency of multiplicity throughout the protostellar phase. The molecular line data enable us to measure the masses of the protostars and we are beginning to identify and characterize the formation environments of both low and intermediate mass protostars. We find clear changes in multiplicity properties with evolution that link back to their formation mechanisms, establishing a foundation from which multiplicity evolution must begin.

Physical and chemical properties during high-mass star formation

Informal Colloquium
Caroline Gieser
ORATED
Max-Planck-Institut für Astronomie, Heidelberg

During high-mass star formation, fragmentation takes place on various spatial scales from giant molecular clouds down to disk scales. At the earliest evolutionary stages, high-mass protostars are still deeply embedded within their parental molecular cloud and can be studied best at high spatial resolution with interferometers at mm wavelengths. The IRAM/NOEMA large program CORE allows us to analyze the physical and chemical properties of a sample of luminous high-mass star-forming regions. The 1 mm dust continuum of the sample shows a large diversity of fragmentation properties. Using the spectral line emission, we are able to determine the physical structure (temperature and density) and molecular content of individual fragmented cores. Even though all regions are classified to harbor high-mass protostellar objects, the molecular content shows a high degree of complexity. By combining the observed core properties, we are able to estimate chemical timescales with the physical-chemical model MUSCLE. We find well-constrained density and temperature profiles in agreement with theoretical predictions. The molecular complexity in the core spectra can be explained by an age spread that is then confirmed by our physical-chemical modeling. The hot molecular cores show the greatest number of emission lines, but we also find evolved cores in which most molecules are destroyed and, thus, the spectra appear line-poor once again. Currently, we are expanding our sample with ALMA 3 mm observations of 11 additional high-mass star-forming regions at different evolutionary stages - from infrared dark clouds to ultra-compact HII regions - in order to further investigate the evolution of the physical and chemical properties on core scales.

Neutron stars: evolution and emission

Main Colloquium
Dr. Evan Keane
ORATED
National University of Ireland, Galway

Neutron stars exhibit many of the most extreme phenomena ever observed. They are also the most precise astrophysical tools in existence. Fortunately they are readily observable, across the electromagnetic spectrum, from Birr to Bonn to Boolardy. In this talk I will describe what is, and is not, known about neutron stars, with particular emphasis on the inter-related topics of their evolution post-supernova and pulsar emission physics. I will describe the difficulties involved in identifying evolutionary tracks for neutron stars, and discuss some potential solutions to these. Considering the growing number of diverse observational classes within the 'neutron star zoo' I will describe how these groups are, and are not, evolutionarily linked to one another. I will also describe search strategies that might identify the most interesting undiscovered sources.

Novel search techniques to detect pulsar black hole binaries in radio observations

Promotionskolloquium
Vishnu Balakrishnan
ORATED
Max-Planck-Institut für Radioastronomie

Pulsars are rapidly rotating highly magnetised neutron stars that emit beams of electromagnetic radiation from their magnetic poles. These compact objects are unique as they are one of the densest forms of matter known in the Universe. Discovering pulsars are a gateway to new and exciting science as they have a wide range of scientific applications from studies of strong-field tests of gravity, neutron star physics and cosmology being a few examples. While all pulsars have their own applications, the bulk of my talk will concentrate on the techniques involved in finding new relativistic binary pulsars particularly the yet to be detected pulsar black-hole binary (PSR-BH) which can be used to test General Relativity and alternate theories of gravity in the quasi-stationary strong-field regime. As I will describe, in my thesis work I improved on our detection sensitivity towards PSR-BH binaries by a factor of 2-2.5 that was achieved purely by changing the search algorithm. I will present the results of my comprehensive search for recycled and unrecycled PSR-BH binaries in circular orbits in the High Time Resolution Universe South Low Latitude Survey (HTRU-S lowlat) using the template-bank algorithm. I will give details about the 20 new pulsars that were found from my searches including a new millisecond pulsar J1743−24 which is a rare intermediate spin-period pulsar in a 70.7-day orbit around a light companion star. Using our non-detections of PSR-BH binaries, I will also present limits on short orbital period PSR-BH binaries near the Galactic-Plane (|b| < 3.5 deg). I will also describe a novel Machine-learning (ML) pulsar candidate classifier using Semi-Supervised Generative Adversarial Networks (SGAN) which achieved better classification performance than the standard supervised algorithms commonly used in the literature using majority unlabelled datasets. Additionally, I will also present the results of the first fully coherent GPU-based radio pulsar search pipeline that can search across all five Keplerian parameters. We compare results from my pipeline to standard time and frequency domain acceleration and jerk search pipelines currently used in the literature. I will discuss its computational feasibility and the binary parameter spaces that have opened up that were previously not accessible. [Referees: Prof. Dr. Michael Kramer, Prof. Dr. Norbert Langer, Prof. Dr. Simon Stellmer, Prof. Dr. Volkmar Gieselmann]