A magnetized scenario for the birth of solar-type stars and protoplanetary disks: observations and models

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

Understanding the first steps in the formation of stars and protoplanetary disks is a great unsolved problem of modern astrophysics. The key to make progress on this topic is to confront theoretical models and high-resolution studies of the youngest protostars, observed less than 0.1 Myrs after the onset of protostellar formation. I will present the recent works we carried out, starting from our early results suggesting that >75% of the youngest protostellar disks are only found at very small radii <60 au (Maury+ 2019). I will also describe our kinematic analysis of envelope rotation (Gaudel+ 2020), which conservation of angular momentum is traditionally blamed for the formation of disks, and present how these observations and new numerical models (Verliat+ 2020) question this well-established paradigm. I will discuss how these observations, coupled to our detection of magnetic fields (Maury+ 2018, Galametz+ 2018, Le Gouellec+ 2019, Galametz+ 2020) may favor a scenario of magnetically regulated protostellar disk formation. Finally, since magnetic fields are routinely mapped thanks to dust polarized emission, we have also investigated the dust properties in young protostars to shed light on the mechanisms responsible for the polarization (Guillet+ 2020, Le Gouellec+ 2020). Confronting our observations against synthetic observations of protostellar MHD models, we were able to show that large (>10 -100 microns) dust grains are required to (i) produce polarized dust emission at levels similar to those currently observed in solar-type protostars at millimeter wavelengths (Valdivia+ 2019), and (ii) explain the variations of dust emissivity observed in protostellar envelopes (Galametz+ 2019).

X-ray binaries as universal tools of astrophysics

Main Colloquium
Dr. Victoria Grinberg
ORATED
Universität Tübingen

X-ray binaries consist of a compact object - a neutron star or a black hole - that accretes matter from a stellar companion. They are usually the brightest sources in the X-ray sky and highly dynamic, with variability scales ranging from millisecond quasi-periodic oscillations and hour- and day-long orbital periods to year-long activity cycles. They change not merely in brightness, but in the very physical processes that cause and modify the X-ray emission. This makes X-ray binaries into versatile tools allowing us to study some of the most important questions in today's astrophysics. I will in particular show that X-ray binaries are unique labs to probe the physics of extreme gravity and to understand accretion and that they can crucially contribute to the understanding of the most massive stars in our universe, in particular their strong and highly structured outflows.

Mergers of neutron-star binaries and their electromagnetic signals

Main Colloquium
Prof. Masaru Shibata
ORATED
Max-Planck-Institut für Gravitationsphysik, Potsdam

The merger of neutron-star binaries (neutron star-neutron star/black hole-neutron star) is the source of gravitational waves, electromagnetic transients, and nucleosynthesis of heavy elements. Numerical simulation in general relativity (numerical relativity) is the chosen approach for clarifying these aspects for the merger. I will first review our current understanding for the merger and post-merger processes of neutron-star binaries, based on the recent results of numerical-relativity simulations. Then, I will talk on electromagnetic signals in the kilonova and radio flare scenarios, which are expected to be detected in the near-future gravitational-wave observations.

Search for repeating bursts from known FRBs observed at the 100-m Effelsberg telescope

Master Colloquium
Sonia Munjal
ORATED
Max-Planck-Institut für Radioastronomie

Fast radio bursts (FRBs) are among the most interesting sources observed in the transient radio sky. FRBs were discovered as bright millisecond duration bursts of high dispersion measure and extragalactic origin. This impulsive emission is a powerful tool for the study of matter constituents in the Universe. Originally detected as one-off transients, some FRBs have been discovered to repeat. In this project, results from a search for repeating bursts from known FRBs in the data observed using the 100-m Effelsberg telescope are presented. A total of 11 FRBs, including the known repeater FRB121102, were observed and data was processed using a single pulse search pipeline. In addition, the machine learning based algorithm FETCH was applied on the data, to detect and differentiate between FRBs and RFI (Radio Frequency Interference) among the burst candidates. Except for FRB121102, no bursts were detected from the targets. Finally, we place limits on the non-detections based on the properties of the known repeating FRB121102.

The Universe, Seen in the Far-Infrared

Main Colloquium
Prof. Joaquin Vieira
ORATED
University of Illinois, Urbana-Champaign, USA

I will present an overview of observations, technologies, and facilities observing the evolution of the Universe in the (far-)infrared, from 2 to 2000 microns (um) in wavelength. I will begin with current efforts to study the cosmic microwave background (CMB, 1000-4000um), the relic radiation left over from the Big Bang. I will present an overview of the rich scientific questions currently being pursued by CMB experiments, which ties together the most disparate scales possible in science: quantum mechanics and cosmology; the beginning of the universe to the present day. I will transition to studies of high-redshift galaxy evolution with the Atacama Large millimeter/submillimeter Array (ALMA 450-3000um) and the future with the James Webb Space Telescope (2-30um). Understanding the formation and evolution of galaxies is one of the foremost goals of astrophysics and cosmology today and these two facilities are, and will be, providing exciting new insights into these key questions. The far-infrared (50-500um) portion of the electromagnetic spectrum provides a unique window into the evolution of the Universe and, while difficult, far-infrared spectroscopy is crucial for studies of the interstellar medium, galaxy evolution, and the high-redshift Universe. I will also discuss new instruments on the ground and in space which will significantly expand our discovery reach with the (far-)infrared into the coming decades.

Active Galactic Nuclei: fueling and feedback

Main Colloquium
Prof. Françoise Combes
ORATED
Observatoire de Paris and Collège de France, Paris, France

Dynamical mechanisms are essential to exchange angular momentum in galaxies, drive the gas to the center, and fuel the central super-massive black holes. While at 100 pc scale, the gas is sometimes stalled in nuclear rings, recent observations reaching 10 pc scale, or 60 mas with ALMA, have revealed, within the sphere of influence of the black hole, smoking gun evidence of fueling. Observations of AGN feedback will be described, together with the suspected responsible mechanisms. Molecular outflows are frequently detected in active galaxies with ALMA and NOEMA, with loading factors between 1 and 5. When driven by AGN with escape velocity, these outflows are therefore a clear way to moderate or suppress star formation. Molecular disks, or tori, are detected at 10 pc-scale, kinematically decoupled from their host disk, with random orientation. They can be used to measure the black hole mass.

The Gravitational Universe of LISA in the Era of Multimessenger Astronomy

Main Colloquium
Prof. Monica Colpi
ORATED
University of Milano Bicocca

In my talk I will first give an overview of the prospected gravitational wave sources that the ESA-led space mission LISA will detect. I will then explore the potential of detecting X-ray light from coalescing massive binary black holes in concurrent observations with the ESA-led mission Athena to show that these may provide breakthrough in areas beyond those each individual mission can achieve in all domains, from Physics to Cosmology and Astrophysics.

Using scintillation to study the variable scattering and orbital motion of PSR J1643-1224

Master Colloquium
Geetam Mall
ORATED
University of Cologne

Scintillation is caused by multi-path propagation of a pulsar signal through the interstellar medium which produces an interference pattern in time and frequency. The additional time delays induce pulse broadening when observed on Earth, which can contribute significantly to the noise in high-precision pulsar timing, a technique which helps to test theories of gravity, and potentially detect gravitational waves. LEAP (the Large European Array for Pulsars) is the combination of the five largest European radio telescopes. Its goal is to increase sensitivity of pulsar timing observations. In this thesis we present five years of LEAP data for the pulsar J1643-1224, which is part of pulsar timing arrays. PSR J1643-1224 lies directly behind an HII region at a distance of around 148 pc, making it an interesting source for determining the effects of scintillation and scattering on precision timing. Despite an environment which should lead to large amounts of scattering, we see a clear parabolic scintillation arc for PSR J1643-1224, which varies in curvature throughout the year. We hypothesise that a thin scattering screen leads to these scintillation arcs, and that this screen lies within the intervening HII region. In this thesis we fit the observed arc curvature variations to measure the distance and orientation of the scattering screen, and obtain an orbital constraint for the pulsar's binary system. During our analysis, we find that our calculated distance to the scattering screen is consistent with the known distance to the HII region. We also measure the variation of scattering delays for this pulsar overtime to see if variable scattering can explain an unusual timing event seen for this pulsar during 2015 by multiple telescopes. We find that our measured scattering time delays are too low to explain the unusually late arrival times of the pulses during this period. [Referees: Prof. Michael Kramer (MPIfR), Prof. Peter Schilke (University of Cologne)]

Searching for continuous gravitational waves

Main Colloquium
Dr. Maria Alessandra Papa
ORATED
Max-Planck-Institut für Gravitationsphysik, Hannover

There has been much excitement about the first gravitational wave detection and the first multi-messenger signal. Since those landmark results LIGO/Virgo have detected a number of signals, all from the merger of compact objects. We expect however a broader variety of signal morphologies, reflecting a broader range of astrophysical phenomena. In this talk I will concentrate on continuous signal, the gravitational wave equivalent of pulsar signals. I will describe the main features of the detection problem, results to date, open questions and future prospects.

TBD

Main Colloquium
Dr. Marco Berton
CANCELED
Finnish Centre for Astronomy with ESO, University of Turku, Finland

TBD

Investigation on gravitational star-disk encounters producing \‘Oumuamua and Borisov-like Interstellar Objects

Master Colloquium
Luis Lauro Aizpuru Vargas
ORATED
Max-Planck-Institut für Radioastronomie and Forschungszentrum Jülich

The recent discovery of two Inter-Stellar Objects (ISO) in our own Solar System has prompted astronomers to come up with theoretical explanations on how they are produced. Most newly formed stars are initially surrounded by a protoplanetary disks. The main hypothesis is that these ISOs were planetesimals in such disks and that through one mechanism or another became unbounded to their host stellar system. These same stars are preferentially formed in stellar clusters. The gravitational effects that result from the interaction between disks and stars are thus common and relevant for the understanding of the fate of such disks. Amongst these mechanisms there is the gravitational stellar fly-by encounter. The partial destruction of the disk by the perturber star produces a varying number of unbounded planetesimals. Several studies have looked into the effects of stellar fly-bys on disks both for the co-planar prograde case and for inclined retrograde cases. They investigated properties such as final disk size or final fate of the test particles. However, the particles that become unbound have attracted little attention so far. This work focuses on the particles that become unbound during such fly-bys contributing to the ISO population. We perform numerical simulations of a range of parabolic inclined encounters with varying pertuber star masses and periastron distances for the encounters. The parameter space explored in this work is relevant for a typical stellar cluster environment. Here we focus on the relative amount and the velocities of ISOs produced during such a fly-bys. We found that the velocity distribution of unbounded test particles varies according to the different possible combination of parameters. Nonetheless, the velocities were found to be in the range between 0.3 km/s and 3.0 km/s. These results can be applied to cluster simulations as to determine the velocities of ISOs the cluster as a whole produces. Using the results of this particular work along with the available literature on the velocities of ISOs produced by other sources, we can make a quantitative distinction between the different types of ISOs. As a follow up study, more precise cluster simulations accounting for the IMF function and considering binary populations and viscous disks would provide a more realistic and comprehensive study of the production of ISOs in clusters. [Referees: Prof. Susanne Pfalzner, Prof. Pavel Kroupa]

Stellar populations in gravitationally bound systems

Promotionskolloquium
Tereza Jerabkova
ORATED
HISKP, University of Bonn

Stars form in dense sub-parsec regions of molecular clouds, while at the same time, star-forming regions are inevitably coupled to the galactic gravitational potential. This talk will address the complex multi-scale physical nature of star-formation by combining a detailed investigation of resolved star-forming regions using Gaia data with theoretical modelling of stellar populations. In particular, the discovery and my confirmation and theoretical explanation of the unexpected existence of three stellar populations in the young Orion Nebula Cluster present a clear example of the importance of pc-scale processes such as stellar dynamics on star and star-cluster formation. Furthermore, I will present the discovery, made possible with the advent of the Gaia space mission, of 100-pc long and few-pc thin co-eval filaments of star formation, a new fact posing novel viable constraints for theories of star-formation. Using these, and previous, constraints on star formation, I build bridges to the galactic scales using the Integrated Galactic Initial Mass Function (IGIMF) theory. The publicly available code, GalIMF, has been co-developed within my doctoral studies to synthesise stellar populations of whole galaxies. This allowed me to compute, for the first time, a large grid of the empirically driven variable galaxy-wide stellar initial mass function for direct comparison with observations. This modelling and the associated code were used, for example, to construct the cosmic star-formation history with a variable stellar-initial mass function. In a nutshell, I aim to present a multi-scale and multi-technique contribution to star-formation and stellar populations opening novel and original routes for future research. [Referees: Prof. Dr. Pavel Kroupa, Prof. Dr. Karl Menten, Prof. Dr. Simon Stellmer, Prof. Dr. Hubert Schorle, Prof. Dr. Andrew Hopkins]

Collisions of free radicals and astrophysical chemistry

Special Colloquium
Dr. Sarantos Marinakis
ORATED
University of East London, UK

The past thirty years have seen an increased understanding of the role that free radicals play in astrophysical chemistry. This has been achieved by advances in spectroscopy and computational methods. The work described in this talk has focused on the role of OH, CH and PO radicals and in particular in collisions with He. The calculation of the inelastic rate coefficients of these 2pi radicals in collisions with He is a complex task because these open-shell systems are described by two adiabatic potential energy surfaces (PESs), and the radicals can populate different energy levels characterized by spin-orbit, rotational, lambda-doublet and hyperfine quantum numbers. For this reason, new ab initio PESs have been obtained, and accurate fully quantum close-coupling scattering calculations have been performed. The calculation of the inelastic rates for relevant reactions combined with existing spectroscopic work showed the role of inelastic collisions in various interstellar media (ISM). In particular, we examine their role in the ISM and in masers. Finally, the role of PO in prebiotic chemistry is also examined.

Termination of red giant evolution through the common-envelope process: Formation of disks, jets, and other phenomena

Main Colloquium
Prof. Hans Olofsson
CANCELED
Onsala Space Observatory, Sweden

TBD

Down the Dusty Road -- Gems from Large (sub)-millimetre Surveys

Main Colloquium
Prof. Thomas Greve
ORATED
Dept. of Physics and Astronomy, University College London, UK

In the last decade, single-dish (sub-)millimetre surveys covering 100-1000 square degrees on the sky have allowed for the harvesting of 100s of strongly gravitationally lensed (magnification factors >10) high-z dusty starburst galaxies -- objects that due to their lensing-configuration are too rare to be uncovered in significant numbers in smaller surveys. These objects, owing to their brightness, are 'easy pickings' for follow-up observations with ALMA and Hubble, and have proven to be a treasure for studying the most extreme dusty starburst galaxies back to 800 million years after the Big Bang. In this talk I will present the latest results from the South Pole Telescope Submillimeter Galaxy Survey (SPT-SMG), which has produced the largest and best-studied sample of lensed starburst galaxies in the young Universe. Finally, I will talk about plans to conduct large mm-surveys from the Arctic, using the 12meter Greenland Telescope, currently located at Thule Airbase.

(Online PhD Colloquium) - TBD

Promotionskolloquium
Ms. Efthalia Traianou
CANCELED
MPI für Radioastronomie

(Online PhD Colloquium) - TBD

High Resolution VLBI Studies of the Blazars TXS 2013+370, OJ 287, and 3C 454.3

Promotionskolloquium
Ms. Efthalia Traianou
ORATED
MPI für Radioastronomie

Blazars are the most luminous sub-class of active galactic nuclei (AGN). Powered by an accreting supermassive black hole (SMBH), these systems are characterized by an axisymmetric pair of powerful relativistic jets that emanate from their central region and are closely aligned to our line of sight. Thanks to this geometrical coincidence, blazars constitute a unique case of astrophysical objects in which we can study the extreme physical conditions associated with the jet launching region and the strong magnetic fields in the vicinity of the central engine. To date, a number of open questions are related to those objects. In this thesis, the origin of the high-energy emission and the seed photon field, the true nature of the observed jet base, and the jet phenomenology are investigated. For this purpose, we employ a state-of-the-art observational technique called Very-Long-Baseline Interferometry (VLBI). Simultaneous radio observations at 86 GHz using the largest radio antennas in the world, as well as complementary observations of ground array elements with the space radio telescope RadioAstron, give us the unique opportunity to focus on three case studies: the blazars TXS 2013+370, OJ 287 and 3C 454.3. [Referees: Prof. Dr. Anton Zensus, Prof. Dr. Andreas Eckart, Prof. Dr. Carsten Münker, Dr. Steffen Rost]

NLS1 galaxies from radio to gamma-rays

Main Colloquium
Dr. Marco Berton
CANCELED
Finnish Centre for Astronomy with ESO, University of Turku, Finland

TBD

A matter of dark matter: what cosmological simulations can tell us about particle physics

Main Colloquium
Dr. Sylvia Plöckinger
CANCELED
Lorentz Institute for theoretical physics, Leiden University, The Netherlands

TBD

The excitation of methanol in massive star-forming regions

Master Colloquium
Jiwoong Jang
ORATED
Max-Planck-Institut für Radioastronomie

Massive star formation and how the physical conditions of its environment change with evolutionary stages are an active field of research. Methanol is a good tracer to probe the physical characteristics of massive star-forming regions (MSFRs) because of its physical properties, abundance, and widespread distribution in dense clouds. Thus, to verify how the environments in MSFRs along various stages of evolution are affected and changed, we present a methanol study of the 100 brightest clumps selected from the ATLASGAL dust continuum survey of the Galaxy, with a range of infrared properties. For four representative clumps, methanol in line surveys in various frequency ranges was studied in detail and, based on the results, selected methanol lines were subsequently analyzed in a statistical approach in the full sample. We determined peak velocities, widths, and integrated intensities by using a Python-based Gaussian fitting code to investigate their kinematics, excitation from rotation diagrams, and to compare line ratios with RADEX simulations. We find a variation of peak positions in terms of the excitation energies in G34.26, and broadened profiles in G23.21. Rotation diagrams show distinct groups of line intensities with different critical densities and excitation energies. Finally, results are presented for statistical trends with evolutionary stages for column densities, temperatures, E/A ratios and volume densities. [Referees: Prof. Dr. Karl Menten, Prof. Dr. Pavel Kroupa]

disregard - this is a test

Lunch Colloquium
Dr. Anaëlle Maury
ORATED
CEA Saclay

disregard - this is a test

Radio AGN and their role in galaxy evolution

Informal Colloquium
Dr. Eleni Vardoulaki
ORATED
MPI für Radioastronomie

- Our current understanding through observations and simulations requires galaxy growth to be regulated by outflows from active galactic nuclei (AGN), in order to avoid having overly massive galaxies in the local Universe. AGN are known to affect their hosts by providing feedback in two modes: radiative (or quasar mode), which is observed at X-rays, and kinetic (or jet/radio mode), which is observed in the radio. AGN regulate massive galaxy growth by heating (negative feedback) the gas responsible for star formation and by displacing the gas in the circum-galactic medium, thus quenching star formation in their host galaxies. From observations, the radio-mode feedback, which is caused by the kinetic energy released from jets, has been shown to be more efficient in quenching star-formation. In this seminar I will present state-of-the-art observations of the COSMOS field (2.3 uJy/beam, 0”.75 resolution at 3-GHz VLA-COSMOS; Smolcic et al. 2017) and will discuss the link between radio AGN, their massive hosts and the large-scale environment.

The Origin of Interstellar Turbulence

SFB Colloquium
Prof. Mark Krumholz
ORATED
Australian National University, Canberra

[The link to the video conference will be sent in a separate email.] In this talk, I review attempts to build a self-consistent model for the origin of turbulence in the interstellar medium (ISM) of star-forming galactic discs. Ideally such a model would incorporate all potential sourcesof turbulence: stellar feedback, gravitational and other instabilities, and driving by stellar gravity, and would be able to explain observed correlations between ISM turbulence and other properties of galaxies, such astheir star formation rates. I summarise the various ways that theorists have attempted to fit together physical ingredients to reach this goal, the differing physical pictures behind these models, and the strengths and weaknesses of each when it comes to reproducing the observations. I then show that it is possible to combine the best elements of these models into a single, unified picture that explains the relative roles of the various sources of turbulence, and successfully reproduces most of the major observations. I suggest future observations that can be used to test this unified model.

TBD

Main Colloquium
Prof. Ludovic van Waerbeke
CANCELED
University of British Columbia, Canada

TBD

TBD

Main Colloquium
Dr. Esra Bulbul
CANCELED
Max-Planck-Institut für extraterrestrische Physik

TBD

(Online colloquium) - Precessing jets in AGN - potential signatures of supermassive binary black holes

Informal Colloquium
PD Dr. Silke Britzen
ORATED
MPIfR

Online colloquium; please use link - Active Galactic Nuclei (AGN) have been observed since decades with very long baseline interferometry (VLBI) to trace the structural changes in their parsec scale radio jets. In addition, these AGN have been monitored across the wavelength regime (from the radio- to the high energy TeV-regime) to monitor their flaring properties. It is expected that the combination of the two kinds of information yields insight into the feeding of the central engine (widely believed to be a supermassive black hole). We propose that the AGN flux variability can have a geometric/kinetic origin, arising from time-variable Doppler beaming of the jet's emission as its direction changes due to precession (and nutation). The most promising mechanism causing such jet precession is the presence of a secondary black hole near the center of the AGN. I will present and discuss our recent results and best cases for a precession origin of the flux variability and kinematic evolution.

A 3-mm Imaging Line Survey of The Central Molecular Zones of M 82 and IC342

Promotionskolloquium
Céline Chidiac
ORATED
Max-Planck-Institut für Radioastronomie

The central molecular zones of two nearby galaxies M 82 and IC 342 are among the most prominent extragalactic molecular sources in the northern hemisphere. While M 82 is a relatively small late type starburst galaxy, IC 342 is a spiral galaxy similar to the Milky Way in many respects, but seen face-on. While the two galaxies share many properties such as global molecular gas mass, H2 column densities, and density of bulk gas, they differ in their star formation rates. In order to investigate how the star formation rate depends on the physical environments, conditions, and chemistries, the molecular content of the central molecular zones of M 82 and IC 342 has been studied, and different environmental conditions, e.g. shocks, hot cores, photo-dissociation regions were traced. The results showed that in M 82, the gas is affected by photo-dissociation regions and emission from massive stars, as traced by H alpha lines. The detection of N2H+ in M 82 indicates the presence of a quiescent gas with a visual extinction higher than 20 mag, that can act as gas reservoir and fuel future star formation. On the other hand, in IC 342, shocks (traced by SiO and HNCO) are dominating the heating processes, thus halting the star formation. [Referees: Prof. Dr. J. Anton Zensus, Prof. Dr. Frank Bertoldi, Prof. Dr. Klaus Desch, Prof. Dr. med. Rainer Schalnus] Note: The colloquium will be held online per videoconference. Detailed information will be provided per email.

The interplay between gas, dark gas, and cosmic rays in the local interstellar medium

Main Colloquium
Prof. Isabelle Grenier
CANCELED
Université Paris Diderot and CEA Saclay, France

TBD

(Online Colloquium) - Updating the unification of jetted AGN

Informal Colloquium
Dr. Olivier Hervet
ORATED
Santa Cruz Institute for Particle Physics

Informal colloquium substituting the lunch colloquium held online, please use the link: Active galactic nuclei (AGN) with jets are the most energetic stationary systems in the universe, shining in all wavelengths from radio to very-high-energy gamma rays (E>100 GeV). Jetted AGN were historically classified from their optical features and large scale radio jet morphology without a clear link between the sources due to the great variety of their observed relativistic beaming. In the early 90's the general unification of jetted AGN was set, presenting a clear dichotomy between low power sources known as "BL Lac objects" and high power ones known as "Flat spectrum radio quasars" (FSRQs). However, the progress made in this last decade with intensive observing multiwavelength campaigns, and better sensitivities in all the electromagnetic spectrum, increasingly highlight sources with complex behaviours not fitting into the usual classification. I will show how the parsec-scale imaging from radio very-long-baseline-interferometry (VLBI) observations coupled to broadband spectral models and hydrodynamic jet simulations lead us toward an updated unification scheme of the jetted AGN phenomenon.

TBD

Main Colloquium
Prof. Masaru Shibata
CANCELED
Max-Planck-Institut für Gravitationsphysik, Potsdam

TBD

(Online Colloquium) - Earth-Orbit Aperture Synthesis

Informal Colloquium
Dr. Alan Roy
ORATED
MPIfR

Online colloquium per videoconference, please use: -- I investigate the idea that VLBI might be done between one antenna and itself as it moves along the Earth's orbit, provided the bandwidth is sufficiently small that the coherence time is longer than the time needed for the antenna to sweep out the baseline. Such a technique offers the tantalizing prospect of synthesizing space-VLBI-like baselines without needing a satellite, or the ability to fill in missing short baselines in EVN. However the initial result from a numerical model is that it does not work, at least for uniform linear motion, for an interesting reason. But maybe there is still hope for accelerated reference frames, such as in the Earth's orbit around the sun?

(Online Colloquium) - Constraints on the magnetic field in the Galactic halo from globular cluster pulsars

Informal Colloquium
Dr. Federico Abbate
ORATED
MPI für Radioastronomie

Talk held remotely per videoconference, please use link - The Galactic magnetic field plays an important role in the evolution of the Galaxy, but it is not known whether the Galactic field permeates the halo of the Galaxy. By observing pulsars in the halo globular cluster 47 Tucanae, we have probed the Galactic magnetic field at arcsecond scales, discovering an unexpected large gradient in the component of the magnetic field parallel to the line of sight. This gradient is aligned with a direction perpendicular to the Galactic disk and could be explained by magnetic fields amplified to some 60 μG within the globular cluster. Such a scenario supports the existence of a magnetized outflow that extends from the Galactic disk to the halo and interacts with 47 Tucanae.

TBD

Main Colloquium
Dr. Victoria Grinberg
CANCELED
Universität Tübingen

TBD

(Online Colloquium) - Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

Informal Colloquium
Dr. Jae-Young Kim
ORATED
MPI für Radioastronomie

Talk held remotely per videoconference, please use link 3C 279 is an archetypal blazar with a prominent radio jet and shows broadband flux density variability across the entire electromagnetic spectrum. There is ample observational evidence that the variable emission, which changes even on ~5 minutes timescales, originates from the the ultra-compact nucleus of the jet. While previous ground-based very long baseline interferometry (VLBI) observations at cm-wavelengths characterized the structure and dynamics of the jet on parsec (milliarcsecond) scales, the limited angular resolution did not allow a direct view into the microarcsecond-scale fine structures within the cm-VLBI core. In this talk, I will show results from recent Event Horizon Telescope (EHT) observations of 3C 279 at 230 GHz. The source was observed during four days in April 2017, along with M87, at a record angular resolution of ~20 microarcseconds (~0.13 pc ~1700 Schwarzschild radii spatial resolution). Main results including the highest resolution images and complex dynamics of the ultracompact jet, and their physical interpretations will be presented.

(Online Master Colloquium) - Relativistic Magnetohydrodynamic Simulations and Ray-Tracing

Master Colloquium
Ms. Joana Anna Kramer
ORATED
MPI für Radioastronomie

Master Colloquium (Online Presentation) - Please use zoom link -- Relativistic jets emanating from the centers of Active Galactic Nuclei (AGN) are among the most energetic objects on the universe. Through the use of 3D relativistic magnetohydrodynamic (RMHD) jet simulations (with the PLUTO code) we set about studying how the jet's synchrotron emission depends upon (i) the morphology of the jet's magnetic field structure and (ii) the micro physics of particle acceleration within the jet. In particular, we create synthetic ray-traced images of the jet's polarized synchrotron emission when the jet carries a predominantly poloidal, helical, and toroidal magnetic field. We also explore several scaling relations in which the underlying electron power-law distribution is set proportional to (i) the jet's thermal plasma density, (ii) the jet's internal energy density, and (iii) the jet's magnetic energy density. Through the application of polarized radiative transfer and ray-tracing ( via the RADMC-3D code) we create synthetic radio maps of the jet's total intensity as well as linearly polarized and circularly polarized intensity for each jet simulation. Finally, we have recently begun experimenting with a new 'particles' module contained in the latest version of the PLUTO code. This new module contains a state-of-the-art algorithm for modeling diffusive shock acceleration and synchrotron cooling within our RMHD jet simulations. [Referees: Prof. Dr. Eduardo Ros, Prof. Dr. Norbert Langer]

The sharpest view of blazar jets through space and millimeter VLBI observations

Main Colloquium
Dr. Jose Gómez
CANCELED
Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain

Mass accretion onto the supermassive black holes that power AGN leads to the formation of highly collimated relativistic jets that radiate across the entire electromagnetic spectrum, from radio to gamma-rays. Over the past decades, AGN jets have been repeatedly studied through centimeter VLBI observations, but the resolution provided is just a step behind the one necessary to resolve the compact regions in the vicinity of the central black hole where jets are formed, collimated, and accelerated. This limitation has recently been overcome by two technological improvements. On one side, the space VLBI mission RadioAstron has allowed us to increase the virtual size of our VLBI telescopes to as large as the distance to the Moon, achieving angular resolutions as small as 20 microarcseconds. On the other side, the participation of ALMA in millimeter VLBI arrays, such as the EHT and GMVA, has not only allowed the EHT to capture the first image of a black hole, but also holds the potential to actually address for the first time the fundamental questions of how gravity works in the strong-field regime near the event horizon, how accretion leads to the formation of relativistic jets, and what are the sites and mechanisms for the production of high energy emission in blazars. In this talk we summarize the results from our RadioAstron Key Science Program, which in combination with quasi-simultaneous GMVA and EHT observations provides us the sharpest view of blazar jets to probe the magnetic field and innermost jet regions in a sample of the brightest blazars to test jet formation models.

(Online colloquium) - Observational evidence for the origin of high-energy neutrinos in parsec-scale nuclei of radio-bright active galaxies

Informal Colloquium
Mr. Alexander Plavin
ORATED
Astro Space Centre Lebedev & Moscow Inst. Phys. & Technology, Moscow, Rusia

Informal colloquium (substituting lunch colloquium at an earlier time) held remotely via zoom, please use link: Observational information on high-energy astrophysical neutrinos is being continuously collected by the IceCube observatory. However, the sources of neutrinos are still unknown. In this study, we use radio very-long-baseline interferometry (VLBI) data for a complete VLBI-flux-density limited sample of active galactic nuclei (AGN). We address the problem of the origin of astrophysical neutrinos with energies above 200 TeV in a statistical manner. It is found that AGN positionally associated with IceCube events have typically stronger parsec-scale cores than the rest of the sample. The post-trial probability of a chance coincidence is 0.2%. We select the four strongest AGN as highly probable associations: 3C279, NRAO530, PKS1741-038, and OR103. Moreover, we find an increase of radio emission at frequencies above 10 GHz around neutrino arrival times for several other VLBI-selected AGN on the basis of RATAN-600 monitoring. The most pronounced example of such behavior is PKS1502+106. We conclude that AGN with bright Doppler-boosted jets constitute an important population of neutrino sources. High-energy neutrinos are produced in their central parsec-scale regions, probably in proton-photon interactions at or around the accretion disk. Radio-bright AGN that are likely associated with neutrinos have very diverse gamma-ray properties suggesting that gamma-rays and neutrinos may be produced in different regions of AGN and not directly related. A small viewing angle of the jet-disk axis is, however, required to detect either of them.

THOR - The HI/OH/Recombination line survey of the inner Milky Way

Special Colloquium
Dr. Yuan Wang
CANCELED
Max-Planck-Institut für Astronomie, Heidelberg

To study the properties of the interstellar medium from scales of the Milky Way down to scales of individual star-forming regions in different phases(atomic, molecular and ionized), we carried out a large program, THOR:The HI/OH/Recombination line survey of the Milky Way with the Karl G. Jansky Very Large Array (VLA). We mapped the northern Galactic plane from l=14.5 to 67.4 deg and |b|<1.25 deg in HI 21 cm line, four OH lines, nineteen radio recombination lines as well as the continuum emission from 1 to 2 GHz at an angular resolution of ~20-40”. These data allow us to study the different phases of the ISM from the atomic HI to the molecular OH and the ionized gas in the recombination and continuum emission,thus enabling studies of the cloud formation from the atomic to the molecular phase as well as feedback processes from the forming HII regions back to the ISM. In this talk, I will present the latest results of the survey, and focus on the HI study of the whole survey, then zoom into one giant molecular filament (260 pc long) to present the HI self-absorption study, and compare the kinematics and column density distribution of the atomic hydrogen to the molecular gas (CO).

Molecular Gas and Star Formation Across Nearby Galaxies (and the Milky Way)

Main Colloquium
Prof. Frank Bigiel
CANCELED
Argelander-Institut für Astronomie

This talk will provide an overview of some of the major research areas in our recently established group at the AIfA. While until the last few years extragalactic molecular gas surveys have been largely restricted to estimating masses and distributions often at low resolution based on one or very few CO lines, little information has been gained on the physical conditions of this gas across and among galaxies. With our IRAM EMPIRE survey and follow-up campaigns, probing a variety of different molecular lines at mm-wavelengths, as well as high-resolution, arcsecond-scale CO observations with ALMA, resolving molecular cloud scales across nearby galaxy samples, this is beginning to change. In combination with related efforts as part of our PHANGS collaboration, such as IFU imaging with VLT MUSE or HST observations, this is a powerful data set to derive a detailed inventory of gas physical conditions, star formation, stellar populations, and feedback across nearby galaxies. I will present these surveys, highlight results from EMPIRE and early results from PHANGS, and outline the prospects for the coming years. One of the key results of these efforts is a strong dependence of cold gas properties on host galaxy and dynamical environment within galaxies.

Cosmology Beyond Thermal Equilibrium

Main Colloquium
Prof. Jens Chluba
CANCELED
University of Manchester, UK

Following the pioneering observations with COBE in the early 1990s, studies of the cosmic microwave background (CMB) have primarily focused on the temperature and polarization anisotropies. CMB spectral distortions – tiny departures of the CMB energy spectrum from that of a perfect blackbody – provide a second, independent probe of fundamental physics, with a reach deep into the primordial Universe. New theoretical insights as well as experimental developments demonstrate that the time is ripe to open this unique window to early-universe and particle physics. In this talk, I will provide a broad brush overview of the exciting opportunities awaiting us using CMB spectral distortions as a future cosmological probe.

The origin of stellar masses

Special Colloquium
Prof. Mark Krumholz
CANCELED
Australian National University, Canberra

The mass distribution of newborn stars, known as the initial mass function (IMF), has a distinct peak at a mass slightly less than that of the Sun. This characteristic stellar mass appears to be nearly invariant across a huge range of star-forming environments within and beyond our Galaxy, and seems to have changed little over most of cosmic time. Explaining its origin and universality is one of the oldest problems in theoretical astrophysics, but a fully successful theory eludes us even today. In this talk, I review theoretical attempts to explain the characteristic mass of stars, and discuss recent progress suggesting that we may be within reach of a solution.

High-mass star and cluster formation in the Milky Way: the Herschel/HOBYS, IRAM/W43-HERO and ALMA-IMF view

Main Colloquium
Dr. Frédérique Motte
ORATED
Institut de Planétologie et d'Astrophysique de Grenoble, France

The physical process by which stars inherit their properties, especially their mass, from those of their parental cloud is the fundamental issue that guides all star formation studies. Our knowledge of this legacy has profound implications for many areas of astrophysics, including the cosmic history of star formation in galaxies. The star-formation recipes commonly used, among which the origin of the initial mass function (IMF) and star formation rates (SFR), are considered to be universal and thus independent of galactic environments. Our studies challenge these recipes,which are related to our understanding of star formation. I will present the Herschel discovery of high-density cloud filaments, which are forming clusters of OB-type stars. Given their high star formation activity, these so-called mini-starburst clouds/ridges could be seen as "miniature and instant models" of starburst galaxies. The characteristics of mini-starburst ridges investigated with the NOEMA and ALMA interferometers challenge star formation models and shed light on the origin of massive clusters. In one of these ridges, the measured star formation rate (SFR) contradicts statistical models of star formation rates. Moreover, its measured core mass distribution suggests that the stellar initial mass function (IMF) may not be determined, in these extreme environments, at the prestellar stage. These results motivated the setting up of the ALMA-IMF Large Program, a project, whose source sample, main objectives and first results will be presented.

Direct searches for hidden photon dark matter in the particle mass range of 0.4-2070 neV (0.1-500 MHz).

Lunch Colloquium
Dr. Andrei P. Lobanov
ORATED
MPIfR

Weakly interacting sub-eV particles (WISP) are steadily gaining more prominence as likely candidates for explaining the dark matter. The particular focus of attention is on the QCD axions, axion-like particles (ALP) with masses of 100neV-10 meV (corresponding to the frequency range of 24MHz-2.4 THz). In an even broader range of particle mass, non-thermally produced vector bosons (also termed "hidden photons") related to a broken U(1) gauge symmetry are also among the possible WISP dark matter candidates. at frequencies below ~30 GHz, resonant cavities can be effectively employed for direct searches of hidden photon (and other WISP) dark matter. The WISP Dark Matter eXperiment (WISPDMX) jointly run by the MPIfR and the University of Hamburg is the first direct hidden photon dark matter search probing the particle masses within the 0.8--2.07 ueV (208-500MHz) range with four resonant modes of a tunable radio frequency cavity and down to 0.4 neV (0.1 MHz) outside of resonance. In the first science run of WISPDMX, the dark matter signal was searched for in the 0.1-500 MHz frequency band sampled at a 50 Hz spectral resolution. A total of 22000 spectra were obtained during 10-second integrations made at each individual tuning step of the measurements. No dark matter signal is found, both in the individual spectra reaching minimum detectable power of 8e-19 W and in the averaged spectrum of all the measurements with the minimum detectable power of 5e-22 W attained for a total of 61 h of data taking. A plausible candidate signal at 0.90164783 ueV is still under investigation. The overall WISPDMX measurements provide the most stringent to date exclusion limits on the coupling constant of the hidden photon over the 70-2070 neV range of the particle mass. These results and prospects for further WISP dark matter searches in the 100neV-10 meV range will be discussed in this talk.

The co-evolution between quasars and their host galaxies in the early Universe

Lunch Colloquium
Dr. Yali Shao
ORATED
MPIfR

Nowadays, more than 200 quasars at z > 5.7 are published. There are many observational and theoretical evidence of the co-evolution between quasars and their host galaxies, e.g., star formation rate density peak similar to AGN number density peak at redshift 2–3, some theoretical models and observations with AGN driven outflows. To study the co-evolution between the super massive black holes (SMBHs) and their host galaxies, there are two aspects, one is to find ways to improve the estimation of the mass of the central black holes, and the other is to investigate the host galaxy properties. There still some open questions in this field, e.g., the typical physical conditions and dynamics of the interstellar medium in the nuclear region? SMBH-bulge relationship established at early stage of evolution? In this talk, I will introduce my studies of the [C II] and CO (2−1) emission lines, and the far-infrared dust continuum emission by ALMA, VLA and Herschel towards host galaxies of some bright quasars at z ~ 6. I will discuss the formation and evolution of SMBHs in these bright z ~ 6 quasars may trigger a large number of star forming activities in their host galaxies, and the co-evolution between the SMBHs and their host galaxies may be different from the local Universe.

Testing general relativity using X-ray reflection spectroscopy

Main Colloquium
Prof. Cosimo Bambi
CANCELED
Fudan University, Shangai, China

Einstein's theory of general relativity was proposed over 100 years ago and has successfully passed a large number of observational tests in weak gravitational fields. However, the strong field regime is still largely unexplored, and there are many modified and alternative theories that have the same predictions as Einstein's gravity for weak fields and present deviations only when gravity becomes strong. X-ray reflection spectroscopy is potentially a powerful tool for testing the strong gravity region around astrophysical black holes with electromagnetic radiation. In this talk, I will present the state of the art of this field and the current constraints on possible new physics from the analysis of a few sources.

Gravitational Dynamics of Relativistic Binary Pulsar Systems

Lunch Colloquium
Dr. Vivek Krishnan
ORATED
MPIfR

Pulsars in relativistic binary systems are excellent probes of fundamentl physics and binary evolution. Long term measurements of pulse arrival times from such pulsars enable theory-independent measurements of relativistic dynamics that can then be used to test different theories of gravity. Assuming a theory of gravity, such experiments also provide highly precisee measurements of neutron star masses and insights on their equation of state. In this talk, I will provide an introduction to binary pulsar timing and present recent results from a 20-year long timing campaign of a pulsar-white-dwarf system, PSR J1141-6545.

Shaping of Planetary Nebulae

Main Colloquium
Prof. Leen Decin
ORATED
University of Leuven, Belgium

Since 1918 it has been known that planetary nebulae (PNe) exhibit a wide range of morphologies. Several contending theories have attempted to explain the evolution from a spherical Asymptotic Giant Branch (AGB) wind to a non-spherical PN. ALMA data provide a new perspective by revealing that all winds of a sample of AGB stars exhibit structural complexities. A strong correlation emerges between the prevailing morphology and AGB mass-loss rate. I will discuss that the primordial cause for PNe a-sphericity acts already during the early AGB phase and is most likely due to (sub-)stellar binary activity. Including binary interaction during the AGB evolution resolves several, previously unexplained, AGB and (pre-)PNe phenomena. In addition, I will show that early-type oxygen-rich AGB stars are prime candidates to detect the imprint of planets.

Cosmic structure formation with Kinetic Field Theory in the non-linear regime

Special Colloquium
Dr. Elena Kozlikin
ORATED
Fraunhofer Institute and Heidelberg University

I will give an overview of Kinetic Field Theory, a novel analytic approach to cosmic large-scale structure formation, which provides a density fluctuation power spectrum that agrees well with state of the art N-body simulations well into the non-linear regime. Thus far, the non-linear regime of structure formation is only accessible through expensive numerical N-body simulations since the conventional analytic treatment of cosmic density fluctuations via the hydrodynamical equations runs into severe problems even in a mildly non-linear regime. I will point out how Kinetic Field Theory avoids the difficulties of standard perturbation theory by construction and allows to proceed deeply into the non-linear regime of density fluctuations. I will give a summary of the most important results and recent developments for cosmic structure formation. I will then focus my discussion on how the form of the interaction potential influences the formation of cosmic structures in the highly non-linear regime that is accessible through Kinetic Field Theory and the implications it bears on the density profiles of dark matter halos.

The peculiar ISM at the edge of the CMZ

Master Colloquium
Laura Ann Busch
ORATED
Max-Planck-Institut für Radioastronomie

The Galactic Centre (GC) hosts a huge amount of molecular gas, which is concentrated in giant molecular clouds (GMCs) and cloud complexes in the so-called Central Molecular Zone (CMZ). At the edge of the CMZ, there are two bright cloud complexes: the 1.3 and the 1.6 complex, which are named according to their location at roughly 1.3 deg and 1.6 deg Galactic longitude, respectively. Besides typical Galactic centre gas at velocities <100 km/s, these complexes show gas components at high velocities, i.e., 150-180 km/s. Previous studies of both cloud complexes derived extremely high kinetic temperatures for this high-velocity gas of 200-300 K. So far, a heating source could not clearly be ascribed to these elevated temperatures as both sources lack active high-mass star formation and show dust temperatures of <20 K, however, ubiquitous shocks and turbulence are promising candidates. In order to shed light on physical conditions and chemical composition of this peculiar ISM, we performed excitation studies using a variety of molecules. We mapped the 1.3 and 1.6 complex in the whole 3 mm spectral window with the IRAM 30m telescope and at shorter wavelength with the APEX telescope. We investigated the morphology and derived kinetic temperatures of the gas, H2 number densities, and column densities of selected species in several positions in both complexes. Based on the results, we discussed where the high-velocity gas might come from and what is heating it. In addition, we investigated how the 1.3 and 1.6 complex might be associated with the current GC kinematics theory, in which the gas moves according to a gravitational potential induced by a central stellar bar. [Referees: Prof. Dr. Karl Menten and Prof. Dr. Pavel Kroupa]

Pulsar Scintillation: Friend or Foe?

Lunch Colloquium
MPIfR Robert Main
ORATED
MPIfR

Pulsars scintillate in frequency and time, due to interference between multiple images caused by multipath propogation through the Interstellar Medium. In pulsar observations, this can be both a nuisance and a tool. I will go through the basics of the physics and geometry of pulsar scintillation, as well as a practical application of removing this effect from timing observations. I will also describe efforts towards a more ambitious idea, using the interfering scattered images to study pulsars with ~100km precision, and how this can be used to probe pulsar emission regions and to resolve a pulsar's binary motion.

Understanding the impact of massive star formation on its surroundings in Messier 8

Promotionskolloquium
Maitraiyee Tiwari
ORATED
Max-Planck-Institut für Radioastronomie

Massive stars and massive protostars emit ultraviolet (UV) and far-UV (FUV) photons that give rise to bright HII regions and photodissociation regions (PDRs). HII regions comprise hot ionized gas irradiated by strong UV (h nu > 13.6 eV) radiation from a nearby star or from the high stellar temperatures of the massive protostars, which begin core nuclear-burning while accreting. PDRs are at the interface of these HII regions and the cold molecular cloud shielded from the illuminating star, and here the thermal and chemical processes are regulated by FUV (6 eV < h nu < 13.6 eV) photons. The study of HII regions and PDRs is the study of the structure, chemistry, thermal balance and evolution of a very important part of the interstellar medium (ISM). Using state-of-the-art telescopes: SOFIA, APEX and IRAM 30 m, we performed a large imaging survey in the IR, submillimeter and millimeter regime toward the Lagoon Nebula or Messier 8 (M8). By observing various transitions of rotationally excited species, we were able to constrain the physical conditions (temperatures and densities) of the interstellar gas responsible for their emission and explored the morphology of the region using the kinematic information provided by our observed data. We also investigated the formation process of small hydrocarbons in the high-UV flux PDR of the Lagoon Nebula and found gas-phase chemistry is responsible for the observed hydrocarbon abundances. Furthermore, we studied the embedded star forming region in the eastern region of the Lagoon Nebula, M8 east, using different diffuse and dense gas tracers. [Referees: Prof. Dr. Karl M. Menten, Prof. Dr. Pavel Kroupa, Prof. Dr. Simon Stellmer and Prof. Dr. Hubert Schorle]

From Jy to mJy: a different view of local radio galaxies

Main Colloquium
Dr. Eleonora Torresi
ORATED
INAF-OAS, Bologna, Italy

Radio galaxies are among the most energetic manifestation of the AGN phenomenon: indeed, they are extraordinarily relevant in addressing important unknowns relating accretion onto supermassive black holes (SMBH), the production of relativistic jets and the role played by the surrounding environment in shaping the radio morphology. In the "classical" picture, powerful FR II radio galaxies are associated to efficient accretion disks in their central engines, while less powerful FR Is to inefficient accretion flows. However, this is not a sharp one-to-one correspondence: in fact, there exist sources with radio morphologies typical of FR IIs but characterized by inefficient accretion (i.e. FR II-Low Excitation Radio Galaxies), which put the accretion-ejection connection in doubt. I will present a multi-wavelength study from radio to X-rays of these objects belonging to radio catalogs selected at high (order of Jy) radio fluxes with the aim of shedding light on their nature: do they represent an intermediate evolutionary phase between FR II and FR I, or are they a different class of sources? Finding an explanation for the existence of these cross-population objects is even more urgent in the mJy regime: indeed, the recent advent of large-area surveys (SDSS/NVSS/FIRST) in the local Universe, has revealed a more variegated picture of the Radio-Loud AGN population. This side of the Universe is dominated by the emerging class of compact FR 0s, and more interesting, about 90% of FR IIs are LERGs. The high-energy and multi-wavelength properties of these new sources will be discussed within the more general context of the accretion-ejection scenario.

Star formation - Making complex things understandable

Special Colloquium
Prof. Guang-Xing Li
ORATED
South-Western Institute for Astronomical Research, Yunnan University, China

Star formation is among the most complex processes studied by astronomers to date. It is characterised by a multi-scale interplay between gravity, turbulence, magnetic field, galactic shear as well as ionising radiation. Because of its complexity, the physical mechanisms that drive the star formation remain unclear. I will present a few recent advancements. First, I present results from our recent study in the Galactic Center region, where, because of its unique location, shear can drastically reduce the star formation efficiency. I will present our study on the fragmentation of the Cygnus X region, where we demonstrate how the introduction of novel methods can help us to pin down the dominant process at work. Finally, I argue that in spite of years of reach, there are still plenty of undiscovered mechanisms which would drive star formation, and will present one as an example.

Probing Galactic cosmic rays with small molecules and giant atoms

Special Colloquium
Prof. David Neufeld
ORATED
Johns Hopkins University, Baltimore, USA

In the century following their discovery by Victor Hess in 1912, cosmic rays have been recognized as an important constituent of the Galaxy. With a total energy density somewhat larger than that of starlight, cosmic rays are the dominant source of ionization for the cold neutral medium (CNM) within the Galactic ISM. In starless molecular cloud cores, they are also the dominant source of heating. Thus, cosmic rays play a central role in astrochemistry by initiating a rich ion-neutral chemistry that operates within the CNM, and the cosmic-ray ionization rate (CRIR) is a key parameter in models for the chemistry of the ISM. In this talk, I will discuss recent estimates for the cosmic-ray ionization rate in the Galactic disk, obtained by using a detailed model for the physics and chemistry of diffuse interstellar gas clouds to interpret previously-published measurements of the abundance of four molecular ions: ArH+, OH+, H2O+ and H3+. The CRIR estimates thereby obtained show a remarkably small dispersion from one interstellar cloud to another. At the Galactocentric distance of the Sun, the primary CRIR per H nucleus is ~ 2x10-16 s-1 in both diffuse atomic clouds and diffuse molecular clouds. This value also agrees well the CRIR implied by recent observations of carbon and hydrogen radio recombination lines along the sight-line to Cas A. I will also discuss a recently-selected SOFIA Joint Legacy Program, HyGAL, which (among other things) will greatly expand the number of sight-lines on which ArH+, OH+, and H2O+ have been observed.

Cosmic alchemy in the era of gravitational wave astronomy

Main Colloquium
Prof. Enrico Ramirez-Ruiz
CANCELED
Niels Bohr Institute, Copenhagen, and University of California, Santa Cruz

The source of about half of the heaviest elements in the Universe has been a mystery for a long time. Although the general picture of element formation is well understood, many questions about the nuclear physics processes and particularly the astrophysical details remain to be answered. Here I focus on recent advances in our understanding of the origin of the heaviest and rarest elements in the Universe.

The detailed velocity structure and distribution of CO emission in the Galactic plane

Special Colloquium
Manuel Riener
ORATED
Max-Planck-Institut für Astronomie, Heidelberg

Understanding the detailed velocity structure of molecular gas at Galactic scales is of fundamental importance for understanding structure formation in the interstellar medium in different environments. To efficiently analyze the information contained in large Galactic plane surveys, we have recently developed the GaussPy+ package, which incorporates a machine-learning approach to automatically fit millions of spectra and velocity components. Combined with a Bayesian approach of determining distances to the identified components, this enables us to look for systematic trends that are directly linked to the physical processes in the gas. I will present results from our ongoing project that focusses on exploiting the detailed kinematic information contained within large Galactic plane surveys to improve our knowledge about the molecular gas within the Milky Way, in particular its distribution, its connection with interstellar dust, and the importance of its dynamics on the star formation process. I will discuss global properties we extracted from the gas emission of the Galactic Ring Survey (GRS), such as a characterization of its complexity and distribution along the line of sight. I will also describe our work on the velocity structure of molecular clouds across Galactic environments and how it can give insight to the universality of the turbulent velocity fluctuations that we see in the observations. Moreover, I will present first results of our ongoing efforts to produce a full Gaussian decomposition of the entire SEDIGISM data set, which will be an essential part in our planned homogeneous analysis of the distribution and velocity structure of 13CO in the entire inner Galactic plane.

What drives the cosmic history of star formation?

Main Colloquium
Dr. Roberto Decarli
ORATED
INAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Italy

The cosmic history of star formation tells us when galaxies formed their stars. After decades of multi-wavelength observational efforts, this is now fairly well established out to z>4. This star formation rate per cosmological volume increased from early epochs up to a peak at z~1-2, then dropped by 5-10 times down to present day. What drives such an evolution? In order to answer this question, we need to make a step back and study the *fuel* for star formation, i.e., the molecular gas content in galaxies. Is the cosmic star formation history driven by an evolution of the star formation efficiency, i.e., gas at high redshift were able to form more stars per gas mass than in the local universe? Or is the evolution driven by the amount of gas available for star formation in different cosmic epochs? The ALMA SPECtroscopic Survey in the Hubble Ultra-Deep Field, ASPECS, provides an excellent dataset for such an investigation. This ALMA large program provides a census of molecular gas in high-redshift galaxies through full frequency scans at approximately uniform line sensitivity. The resulting cosmic molecular gas density as a function of redshift shows a factor ~6 decrease from z=2 to z=0. The availability of molecular gas reservoirs at the peak of cosmic star formation thus appears to be the main driver of the cosmic star formation history. Additionally, ASPECS provides us with a new, unbiased portrait on the interplay between the molecular gas content and various properties of their host galaxies (position wrt the main sequence, morphology, AGN activity, etc) which will guide the next generation of theoretical models and numerical simulations of galaxy evolution.

Dense gas and star formation in nearby starburst galaxies with ALMA

Special Colloquium
Prof. Christine Wilson
ORATED
McMaster University, Hamilton, Canada

With its high sensitivity, excellent angular resolution, and wide spectral coverage, ALMA is revolutionizing our view of galaxies in the nearby universe. ALMA is particularly important for studying the dense molecular gas that is the fuel for star formation. Radio continuum emission from ALMA is also an important measure of the star formation rate, particularly in galaxies with high visual extinction such as starburst galaxies and luminous infrared galaxies. Finally, the ALMA archive contains an ever-growing collection of data that can be mined and combined to produce large samples of targets that can match or exceed the amount of observing invested in a single ALMA large program. I will describe our work on the link between dense gas and star formation for a sample of 9 nearby galaxies from the ALMA archive, which includes measuring the resolved Kennicutt-Schmidt star formation law at extreme star formation rate surface densities and identifying a new molecular line that appears to be an excellent tracer of the densest star forming gas.