Neutral gas outflows in luminous galaxies at low and high redshift

Main Colloquium
Prof. Paul van der Werf
ORATED
Leiden Observatory, The Netherlands

Galaxies are not closed boxes. They feed on gas inflow from the cosmic web; conversely, feedback-driven gas outflows remove gas from galaxies again, either temporarily or definitively. The last decade has seen an explosion (no pun intended) in observations of gaseous outflows. These outflows are complex, containing ionized, neutral atomic and molecular components, and come in many types, from small but highly collimated and dense molecular jets to enormous ionized gas halos. I will focus on outflows of two types: compact molecular jets emanating from deeply obscured galactic nuclei, and wide-angle outflows traced by P-Cygni profiles of molecular lines. The latter form outstanding probes of neutral outflows in high-redshift galaxies. I will discuss one example in detail, where we trace the outflow in a redshift 2 galaxy using OH+ as a kinematic tracer. In addition to tracing the outflow parameters, this reveals local conditions and chemistry in the outflowing gas.

Worlds near and far: mapping the state of the Solar System

Special Colloquium
Dr. Michele Bannister
ORATED
Queen's University Belfast

The small bodies of planetary systems record how their systems formed and evolved. Major observational surveys including Pan-STARRS and OSSOS are providing new insight into the physical properties and orbits in both the inner and the outer Solar System. Together with colour measurements of small-body surfaces, it is finally possible to start piecing together the original compositional structure of our protoplanetary disk, even after the scattering from planetary migration that emplaced today’s intricate dynamical structures. New discoveries of interstellar objects mean the compositions of planetesimals from other stars can now be directly compared to those of our local populations. The prospects for discoveries with the next-generation survey facility, the Large Synoptic Survey Telescope, are bright.

Mapping the Ionized ISM in Nearby Galaxies

SFB Colloquium
Dr. Kathryn Kreckel
ORATED
Astronomisches Rechen-Institut, Universität Heidelberg, Germany

The ionized interstellar medium (ISM) provides crucial insights into understanding baryon cycling within disk galaxies and tracing radiative and mechanical feedback from young massive stars. With new VLT/MUSE optical integral field spectroscopy, the PHANGS team now has a wealth of emission line maps that trace different ionization sources and physical conditions across nearby disk galaxies at the 50 pc spatial scales needed to isolate individual ionized regions (e.g. HII regions, supernova remnants, planetary nebulae) from surrounding diffuse ionized gas. I will present our most recent results connecting the molecular gas with observed sites of massive star formation, and measuring the gas phase oxygen abundances across thousands of HII regions. Within the context of the large scale galactic environment, these studies have implications for our understanding of how spiral structure acts to organize and mix the ISM, and regulate star formation.

New Insights into the Milky Way Magnetic Fields through Radio Broadband Spectro-polarimetry

Promotionskolloquium
Yik Ki Ma
ORATED
Max-Planck-Institut für Radioastronomie

Magnetic field is an essential ingredient of the interstellar medium of galaxies. An accurate characterisation of the magnetic field strength and structure of the Milky Way is crucial for complete understanding of many Galactic astrophysical processes. The Faraday rotation effect can be exploited to reveal the strength and direction of the magnetic field component parallel to the line of sight, which are imprinted in the rotation measure (RM) values obtained from radio polarisation observations. In my thesis, I utilised the broadband spectro-polarimetric capability of the Karl G. Jansky Very Large Array (VLA) in L-band (1-2 GHz) to gain new insights into the magnetic fields of the Milky Way in two ways. Firstly, I investigated in the reliability of the NRAO VLA Sky Survey (NVSS) RM catalogue, which is indispensable for the modelling of the global Milky Way magnetic field. In particular, I quantified the effects of npi-ambiguity and off-axis instrumental polarisation on the RM catalogue, and unlocked the full potential of the NVSS RM catalogue for careful studies of Galactic magnetism. Secondly, I performed new radio observations for a direct study of the magnetic fields near the Milky Way mid-plane in the first Galactic quadrant. My new observations led to a drastic increase in the number of reliable RM values by a factor of five in the target sky region. From the new data, I discovered new features in the Galactic magneto-ionic medium, with important implications on the magnetic field ordering mechanism of galaxies. [Referees: Prof. Dr. Michael Kramer, Prof. Dr. Pavel Kroupa, Prof. Dr. Klaus Desch, Prof. Dr. Dietmar Quandt]

Red dwarfs and nearby terrestrial planets: discovery and opportunities

Main Colloquium
Dr. Guillem Anglada-Escudé
ORATED
Institut de Ciencies de l'Espai-CSIC, Institut d'Estudis Espacials de Catalunya, Barcelona, Spain

Red dwarfs, which are stars that are typically born with masses below 0.6 Msun, are the most numerous stars, and comprise about 70% of the stellar population in the Solar neighborhood. Because we rely on indirect methods for detection of exoplanets, this stars provide a number of advantages for the detection of the smallest planets to the point that today we can detect planets with bulk properties and equilibrium temperatures similar to Earth around them. The detection method strongly influences the possible characterization methods and the information that can be achieved. Irrespective of the technique, the nearest stars and their planets are the ones providing best changes for characterizing their atmospheres and searching for evidence for life. I will review the state of the art for exoplanet detection around the nearest stars, and describe the methods and characterisation opportunities that these planets offer.

Radio emission from massive Young Stellar Objects and their surroundings: Characterization and feedback

Promotionskolloquium
Sac Nicté Medina
ORATED
Max-Planck-Institut für Radioastronomie

Massive stars dominate their galactic environments. They play a major role in the energy budget of galaxies and are essential in their evolution. However, their formation is not fully understood. In particular, the physical characteristics of massive Young Stellar Objects (YSOs) are still unclear because they are deeply embedded in their natal molecular clouds obstructing the view at optical and sometimes even infrared wavelengths. The aims of this thesis were both to study the physical properties YSOs and their effects on the interstellar material surrounding them using high angular resolution and multi-frequency data. In particular Very Large Array data of the star-forming region NGC 6334D-F and from the GLOSTAR survey for sources in the Galactic plane have yielded the physical characteristics of a statistically significant sample of YSOs. Turbulence, driven by YSOs in their surrounding material, was analyzed using optical and submillimeter wavelength observations of ionized and molecular spectral lines using a variety of statistical techniques. [Referees: Prof. Dr. Karl Menten, Prof. Dr. Pavel Kroupa, Prof. Dr. Hubert Schorle, Prof. Dr. Simon Stellmer]

Cosmology with Clusters of Galaxies

Main Colloquium
Prof. Jochen Weller
ORATED
Universitäts-Sternwarte München

I will review the cosmological constraints from the Planck satellite. Then I will move on to describe how optically selected clusters can constrain cosmological parameters and elude on the problems. I will finally discuss the ability of Euclid to constrain cosmology with this probe and explore more exotic cosmologies.

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

Special 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.

Probing subatomic physics with gravitational waves from neutron star binary inspirals

Main Colloquium
Dr. Tanja Hinderer
ORATED
University of Amsterdam, the Netherlands

The recent detections of gravitational waves from merging black holes and neutron stars have established gravitational waves as a new cosmological messenger and opened remarkable opportunities for probing the physics of gravity and matter in unexplored regimes. In this talk I will focus on using gravitational waves from binary inspirals to probe the nature of compact objects and their interior composition. This is of particular interest for neutron stars which comprise matter at supra-nuclear density, under conditions not accessible anywhere else in the universe, whose detailed properties remain an important open question in subatomic physics. I will discuss the main gravitational-wave signatures of matter during a binary inspiral, methods for modeling these effects and extracting this information from the data, and what we have learned from the first observation of a neutron star binary inspiral GW170817. I will also highlight additional insights gained from joint electromagnetic counterpart information, and outline future prospects and challenges.

Conception of artificial VLBI signal generation equipment on a GNSS satellite

Informal Colloquium
Ahmad Jaradat
ORATED
Institute for Geodesy and Geoinformation, University of Bonn

The topic of this talk is the conception of a broadband radio signal to be emitted by a satellite. Observations of satellites with VLBI are the only suitable method for directly linking the dynamic reference frame of satellite orbits to the celestial reference frame realized by astrometric surveys of active galactic nuclei (AGN). Previous investigations have shown that embedding satellite observations into regular geodetic VLBI sessions can improve the frame-ties between celestial and terrestrial reference frames. For this reason, the artificial signal received from the satellite should be similar to the radio emission from an AGN as observed from the surface of the Earth. I will present equipment that could, e.g., serve as an additional payload for a Global Navigation Satellite System (GNSS). Results from simulations will be presented. Legal and technical feasibilty aspects will be discussed.

GRAVITY, the Galactic Center, Relativity, and Massive Black Holes

Main Colloquium
Dr. Frank Eisenhauer
ORATED
MPE Garching

The last years have seen a revolution in Optical/Infrared Interferometry. The GRAVITY instrument at the VLTI is now routinely providing milli-arcsecond resolution imaging and micro-arcsecond astrometry, for objects which are order of magnitudes fainter than what has been possible before. In our presentation we give an overview of the GRAVITY discoveries in Galactic Center Black Hole and Active Galactic Nuclei (AGN). Among others we will present the tests of Einstein's theory of general relativity and its underlying principles from precise stellar orbit measurement, and the discovery of highly relativistic, circular motion of hot gas close to the innermost circular orbit around SgrA*. Especially the time resolved astrometry and the polarization measurements of the flaring SgrA* shed new light on the mechanisms driving the accretion / outflow of black holes. We further present some of the GRAVITY results on AGN, including the image of the hot dust around NGC 1068, the sizes and structure for a first sample of AGNs, and the spatially resolved rotation of the broadline region (BLR) of quasars. We will round of the talk by reporting on the ongoing upgrades and plans towards GRAVITY+ all sky milli arcsecond optical interferometric imaging.

Current and future applications of reverberation-mapped quasars in cosmology

Lunch Colloquium
Dr. Michal Zajacek
ORATED
MPIfR

Reverberation mapping (RM) is a powerful technique that allows us to study in detail the dynamics and the structure of the Broad Line Region (BLR) in active galactic nuclei. RM leads to the determination of the time delay between the continuum and the broad-emission line response, which is directly related to the light-travel distance and the monochromatic luminosity of the source, so-called radius-luminosity (RL) relation. The radius-luminosity relationship has been constructed based on the RM in Hbeta emission line for nearby quasars (z<0.7). It was found by Bentz+2013 that the BLR radius depends on the luminosity with the exponent of ~0.5, which is consistent with simple photoionization predictions. Recently, we found (Martinez-Aldama, M. L.+2019) that highly-accreting sources have time lags shorter than expected from the RL relation. When corrected for the accretion-rate effect, a small scatter along the RL relation can be recovered. Based on the corrected time-delays, we were able to determine absolute luminosities and from measured flux densities, we constructed the Hubble diagram of reverberation-mapped quasars. The determined cosmological parameters are consistent with the standard LambdaCDM model within the 2sigma confidendence interval. We conducted the reverberation mapping measurements of MgII broad line towards higher redshifts: the quasar CTS C30.10 (z~0.9; reported in Czerny+2019) and HE 0413+4031 (z~1.37; Zajacek+2019). Using in total 11 quasars monitored in MgII line, we constructed MgII-based radius-luminosity relation, which exhibits the similar slope as well as the accretion-rate effect as the Hbeta-based RL relation for lower redshifts. This provides a promising way for using quasars as standardizable candles (after the accretion-rate correction) for future cosmological studies across a broad range of redshifts.

Investigating the association between maser species and dense Galactic clumps

Lunch Colloquium
Mr. Sam Billington
ORATED
University of Kent

Interstellar masers are a useful signposts of ongoing star formation across the Galaxy and given they have different excitation condition and mechanism they are also a probe of physical conditions and evolutionary stages. Of particular interest are the two class II methanol masers at 6.7 & 12.2 GHz, the 22.2 GHz water maser and the four base transitions of the hydroxyl maser at 1612, 1665, 1667, 1720 MHz. To investigate the relationship between these various maser species and star formation activity, we have matched various maser catalogues to an inner Galaxy population of dense clumps, known to be harbouring star formation, as identified by the ATLASGAL survey. We find association rates for the water, hydroxyl and methanol masers to be 56, 39 and 82% respectively, and maser species are more commonly found in isolation. We derived the physical conditions required for maser emission and our able to determine their turn-on and termination points in the evolutionary sequence and minimum density and luminosity thresholds and statistical lifetimes. We compare these results to the "straw man" evolutionary model for masers described by Ellingsen (2007) and Breen et al. (2010) and find the results are broadly in agreement.

Plasma Lensing of the Black Widow Pulsar

Special Colloquium
Prof. Marten van Kerkwijk
ORATED
University of Toronto, Canada

Pulsars scintillate because their radiation is slightly bent by material along the line of sight, causing multiple images that interfere with each other. I will discuss one of the themes of "Scintillometry 2019", the workshop we are having this week in Bonn, of how the scintillation might be used for very high resolution astrometry. I will describe observations of one particular pulsar, PSR B1957+20, the original black widow pulsar. These were taken to try to resolve the orbit astrometrically, something we have not yet succeeded in doing, but also led to several serendipitous discoveries, of mode changes and giant pulses (and correlations between those), and, most spectacularly, of great variations in pulsar flux near pulsar eclipse (by material surrounding its companion). Some of latter excursions exceed an order of magnitude over our 48 MHz band. The higher magnification events are strongly chromatic, with magnifications reaching over two orders of magnitude in small frequency bands. I will show that in the high-magnification events, the pulsar magnetosphere is resolved, allowing one to estimate the physical sizes of and separation between the emission regions responsible for the main- and inter-pulse. I will also discuss the puzzling lack of evidence for any magnetic field in the lensing plasma.

A cosmic collider: Was the IceCube neutrino generated in a precessing jet-jet interaction in TXS 0506+056?

Lunch Colloquium
PD Dr. Silke Britzen
ORATED
MPIfR

The neutrino event IceCube 170922A, detected at the IceCube Neutrino Observatory at the South Pole, appears to originate from the distant active galaxy TXS 0506+056. Multiwavelength flaring, observed from the radio- to the TeV-regime, is a regular phenomenon of BL Lac objects or blazars. While many other blazers show properties similar to those of TXS 0506+056, only TXS 0506+056 has been identified as neutrino emitter so far. In the talk I will explain that the enhanced neutrino activity during the neutrino flare in 2014–2015 and the single EHE neutrino IceCube-170922A could have been generated by a cosmic collision within TXS 0506+056. Our findings indicate that this AGN might be an atypical blazar.

A cosmic collider: Was the IceCube neutrino generated in a precessing jet-jet interaction in TXS 0506+056?

Lunch Colloquium
PD Dr. Silke Britzen
ORATED
MPIfR

The neutrino event IceCube 170922A, detected at the IceCube Neutrino Observatory at the South Pole, appears to originate from the distant active galaxy TXS 0506+056. Multiwavelength flaring, observed from the radio- to the TeV-regime, is a regular phenomenon of BL Lac objects or blazars. While many other blazers show properties similar to those of TXS 0506+056, only TXS 0506+056 has been identified as neutrino emitter so far. In the talk I will explain that the enhanced neutrino activity during the neutrino flare in 2014–2015 and the single EHE neutrino IceCube-170922A could have been generated by a cosmic collision within TXS 0506+056. Our findings indicate that this AGN might be an atypical blazar.

Probing the Interstellar Medium and Dark Matter with Pulsars

Promotionskolloquium
Nataliya Porayko
ORATED
Max-Planck-Institut für Radioastronomie

Pulsars are rapidly rotating, highly magnetised neutron stars which emit electromagnetic radiation from their magnetic poles in the form of highly collimated beams. Pulsars are known as a powerful tool to probe the interstellar medium (ISM) and its constituents in the Miky Way. In this thesis we focus on probing the non-baryonic entities in the Milky Way, namely interstellar magnetic fields and dark matter. The first part of the thesis is dedicated to the investigation of small-scale turbulent magnetic fields in the Milky Way, which can be probed by monitoring variations in the Faraday rotation measures (RMs) of linearly polarised radiation of pulsars. For this purpose, we use high-cadence, low-frequency observations from a set of selected pulsars carried out with German LOw-Frequency ARray (LOFAR) stations. We find that measured RMs are strongly affected by the highly time-variable terrestrial ionosphere. We have mitigated the ionospheric contribution assuming a thin-layer model of the ionosphere. We conclude that within this approximation the ionospheric RM corrections are accurate to ~ 0.06 - 0.07 rad per m^2 , which defines our sensitivity towards long-term astrophysical RM variations. The second part of this thesis deals with dark matter - a matter which accounts for about a quarter of the energy density of the Universe, and the nature of which is still under debate. The ultralight scalar field dark matter is one of the compelling dark matter candidates, which leaves characteristic imprints in the times of arrival of radio pulses from pulsars. We search for traces of ultralight scalar-field dark matter in the Galaxy using the latest Parkes Pulsar Timing Array dataset that contains the times of arrival of 26 pulsars. No statistically significant signal has been detected. Therefore, we set an upper limit on the local dark matter density. We conclude by discussing the prospects of detecting the fuzzy dark matter with future radio astronomical facilities. [Referees: Prof. Dr. Michael Kramer, Prof. Dr. Frank Bertoldi, Prof. Dr. Simon Stellmer, Prof. Dr. Robert Glaum]

Neutrinos from a blazar jet and the birth of non-stellar neutrino astronomy

Main Colloquium
Dr. Paolo Padovani
ORATED
European Southern Observatory, Garching

IceCube has recently reported the discovery of high-energy neutrinos of astrophysical origin, opening up the PeV (10^15 eV) sky. These observations are challenging to interpret on the astronomical side and have triggered a fruitful collaboration across particle and astro-physics. Last year some very high-energy IceCube neutrinos have been associated with the blazar TXS 0506+056. I will discuss these results, show that TXS 0506+056 is not what it looks like, and conclude with an outlook. The talk is self-contained and requires no previous knowledge of neutrinos or blazars.

Black hole X-ray binaries- accurate distances and natal kicks

Special Colloquium
Pikky Atri
ORATED
ICRAR Curtin University, Perth, Australia

Even though the first black hole (BH) was detected decades ago, the mechanism by which BHs form is not well understood. Theoretical models suggest that BHs are born when a massive star dies, either with or without a supernova explosion. BHs formed following a supernova explosion are hypothesized to get strong natal kicks, whereas direct collapse BHs do not incur such a kick. In order to obtain an observationally constrained natal kick distribution for Black hole X-ray binaries (BHXBs) we use Monte Carlo simulations to determine the probability distribution of the Plane crossing velocity for 16 systems. We measure the peculiar velocity of each system by combining their radial velocities, distances, archival and Gaia proper motions and track their Galactocentric orbits back to the time of Plane crossing. We use the high resolution of Very Long Baseline Interferometry (VLBI) networks in the USA, Europe and Australia to measure the proper motions of 3 new BHXBs. We also use VLBI to obtain the model-independent distance to a BHXB, MAXI J1820+070, by measuring the parallax of the source. In this talk, I will present the implications of this newly constrained kick velocity distribution of BHXBs on the birth mechanism of BHs, on BH-BH mergers, on retention of BHs in globular clusters and on spin-orbit misalignment of BHXBs. I will also report on the parallax measurement of MAXI J1820+070.

Nitrogen bearing molecules in low mass star forming regions

Master Colloquium
Ashly Kanichukunnath Sebastine
ORATED
Max-Planck-Institut für Radioastronomie

A thorough understanding of low-mass star-forming processes will shed light on the formation of our own solar system. The Aquila molecular cloud is an exceptional laboratory characterized by hundreds of dense molecular cores at different early evolutionary stages. In order to study chemical diversity and kinematics at the early stages of low-mass star formation, we observed nitrogen-bearing molecules towards selected 40 dense cores in the Aquila molecular cloud with the APEX telescope. Their column densities and abundances are estimated under the assumption of local thermodynamic equilibrium. DNC and HCNH+ are more abundant in prestellar sources, while DCN is more abundant in protostellar sources. Kinematic analysis suggests that most of the dense cores are transonic. Five sources are found to show the blue-skewed profile, suggestive of infall motions. [Referees: Prof. Karl Menten, Prof. Pavel Kroupa]

Exploring fundamental physics with tests of the equivalence principle from the lab to the Galactic Center

Main Colloquium
Dr. Aurélien Hees
ORATED
Observatoire de Paris, France

The Einstein equivalence principle is at the heart of the theory of General Relativity. This principle is not based on theoretical considerations but rather on experimental facts and is violated in numerous unification scenarios, Dark Matter models and Dark Energy models. In this colloquium, I will review the motivations to test the equivalence principle and present recent experimental results that search for a breaking of the equivalence principle. First, I will focus on preliminary results of the MICROSCOPE space-mission that provide the best test of the universality of free fall and of the Lorentz invariance. Second, I will show how laboratory experiments involving atomic clocks can be used to search for scalar Dark Matter candidates. Finally, I will present two recent tests of the equivalence principle using measurements of short-period stars orbiting the supermassive black hole in our Galactic Center. The first one is related to the measurement of the gravitational redshift of the star S0-2/S2. The second one consists in a search for a variation of the fine structure constant around our Galactic Center.

Spiral Arms as a Tool to Probe Galaxy Evolution

Special Colloquium
Siyue Yu
ORATED
Kavli Institute for Astronomy and Astrophysics, Peking University, China

Spiral arms are very common and spectacular structures in disk galaxies. The two most important properties of spiral arms are their strength and tightness. I study the physical origin of spiral arms and their effects on galaxy evolution through investigating the relationship between spiral properties and galactic properties. In this colloquium, I will first revisit the methods to quantify spiral structure and discuss their measurement limit; Second, I will show how the spiral structure correlate with global galactic properties such as stellar mass, morphology, rotation curve, and color index, and discuss the implication for the origin of spiral arms; Third, I will show that spiral arms observed at bluer bandpass are mildly but statistically significantly tighter than that at redder bandpass, suggesting a long-lived spiral pattern; Finally, I will focus on the effects of spiral arms on galaxy star formation and show that spiral arms may play a significant contributing role in setting galactic specific star formation rate.

On the use of linear polarizers in VLBI

Special Colloquium
Dr. Iván Martí-Vidal
ORATED
University of Valencia, Spain

With the advent of new-generation broadband receivers in VLBI, it is now possible to extend the observing bandwidths up to several GHz (even across different bands, simultaneously). Due to instrumental limitations, these receivers are designed to detect the signals in a linear-polarization basis, which is not convenient for a proper fringe-fitting in VLBI. One way to overcome this problem is to convert the VLBI data into a pure circular basis after the correlation. I will discuss about a polarization conversion algorithm (PolConvert), that solves the linear-to-circular conversion problem at a post-correlation level and with a minimum (residual) polarization leakage. I will show results of PolConvert applied to state-of-the-art VLBI observations with linear polarizers, ranging from mm wavelengths (ALMA-EHT and ALMA-GMVA) to cm (EVN and VGOS). In the case of VGOS, preliminary results of broad-band dispersive fringe fitting and a full-polarization image deconvolution will also be shown.

The First Large Absorption Survey in HI: Solving the evolutionary history of cold gas since z = 1

Main Colloquium
Dr. James Allison
ORATED
Department of Physics, University of Oxford, UK

The First Large Absorption Survey in HI (FLASH) with the Australian SKA Pathfinder (ASKAP) will provide a unique perspective on the cool (T < 1000 K) gas that fuels star formation and black hole growth in galaxies throughout cosmic history. By detecting the HI 21-cm line in absorption towards thousands of distant radio-loud active galactic nuclei we will construct a census of neutral gas in intervening galaxies since the peak of star formation 10 billion years ago. Until recently radio telescopes were unable to carry out wide-field, spectroscopically-blind surveys for 21-cm line absorption. Such as survey with ASKAP is enabled by combining a 30 square degree field of view, 300 MHz instantaneous bandwidth and a band below 1 GHz that is clear of any radio frequency interference. I will discuss how we can measure the fraction of cold-phase atomic hydrogen using a statistical approach based on the number of expected detections. I will present early science results from FLASH, including the first measurements of the 21-cm absorber density at z = 0.7 and the discovery of a massive HI-rich early type galaxy at z = 0.35.

Radio recombination lines observations with the THOR and GLOSTAR Milky Way surveys

Lunch Colloquium
Dr. Michael Rugel
ORATED
Max-Planck-Institut für Radioastronomie

One of the key questions in star formation is the effect of stellar feedback on the interstellar medium and the interplay between atomic, molecular and ionized gas. Regarding the impact of star clusters on molecular clouds, I will present a study on the signatures of feedback detected Radio recombination line (RRL) emission in the star forming region W49A, using data from the THOR survey with the VLA between 1-2 GHz and one-dimensional models of feedback-driven shells (WARPFIELD, Rahner et al., 2019). To better characterize the ionized gas in HII regions in the first quadrant of the Milky Way, the GLOSTAR survey observed C-band RRL emission with the VLA at ~30" resolution. I will present preliminary results on the kinematic and physical properties of the ionized gas in HII regions and the status of the currently-ongoing Effelsberg survey of RRL transitions between 4-8 GHz.

Science with VLBI absolute astrometry

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

The topic of the presentation is VLBI astrometric surveys. The advances in VLBI technology that resulted in a substantial improvement in sensitivity allowed us to observe large samples of active galactic nuclei (AGN). Processing of such observations provided us positions of extragalactic sources with accuracies down to a fraction of a nanoradian and their images. A number of applications, such as space geodesy, space navigation, phase referencing require precise position catalogues. However, analysis of such a rich dataset has a strong potential for interesting science per se beyond practical applications. In particular, comparison of VLBI and Gaia absolute positions revealed interesting phenomena and provided us a new tool for probing innermost regions of the AGNs. We can run a population analysis with a number of members in the sample counted by thousands. In particular, this dataset gives us a clue to answer the question whether the AGNs that power flat spectrum sources have distinctive properties. A collection of visually binary sources provides a sample for their further scrutinizing and revealing compact symmetric objects (CSO), true binary, and gravitational lenses.

The Order and Disorder of Blazar Jets

Special Colloquium
Prof. Alan Marscher
ORATED
Boston University

The presentation will review progress toward understanding blazars that multi-waveband monitoring observations have advanced. The primary techniques include time sequences of monthly VLBA images and less frequent GMVA and EHT images at millimeter wavelengths, compilation of radio through gamma-ray light curves, linear polarization vs. time at radio and optical wavelengths, and spectral energy distributions (SEDs). Some patterns are apparent in the data, suggestive of order in these systems. However, much disorder is apparent as well, which implies that turbulence (or another source of disorder such as instabilities) plays a major role. An overall picture of blazar jets that incorporates turbulence superposed on the order imposed by narrow jets and shock waves shows promise toward explaining the observations. The future X-ray polarimetry mission IXPE can test whether a key aspect of this scenario - selective particle acceleration in turbulent cells crossing shock fronts - actually occurs.

The VLBA-BU-BLAZAR Program: Linear Polarization in Parsec-scale Jets of gamma-ray blazars

Special Colloquium
Dr. Svetlana Jorstad
ORATED
Boston University and St. Petersburg State University

Since 2008 June, the BU blazar group has been carrying out monthly monitoring with the Very Long Baseline Array at 43 GHz of a sample of gamma-ray blazars, alongside optical photometric and polarimetric observations at the Perkins telescope of Lowell Observatory (Flagstaff, AZ). I will present general results on polarization parameters at 43 GHz of the VLBI cores for different sub-classes of blazars and compare them with those of polarization parameters at optical wavelengths. I will discuss common patterns and differences seen in the polarization behavior for different sub-classes and make some conclusions about properties of the magnetic field in the parsec-scale jets of blazars.

Untangling the Galaxy

Special Colloquium
Dr. Marina Kounkel
ORATED
Physics and Astronomy Department, Western Washington University, USA

Gaia DR2 provides unprecedented precision in measurements of the distance and kinematics of stars in the solar neighborhood. Through applying unsupervised machine learning on DR2's 5-dimensional dataset (3d position + 2d velocity), we identify a number of clusters, associations, and co-moving groups within 1 kpc and |b|<30 deg (many of which have not been previously known). We estimate their ages with the precision of ~0.15 dex. Many of these groups appear to be filamentary or string-like, oriented parallel to the Galactic plane, and some span hundreds of pc in length. Most of these strings lack a central cluster, indicating that their filamentary structure is primordial, rather than the result of tidal stripping or dynamical processing. The youngest strings (<100 Myr) are orthogonal to the Local Arm. The older ones appear to be remnants of several other arm-like structures that cannot be presently traced by dust and gas. The velocity dispersion measured from the ensemble of groups and strings increase with age, suggesting a timescale for dynamical heating of ~300 Myr. This timescale is also consistent with the age at which the population of strings begins to decline, while the population in more compact groups continues to increase, suggesting that dynamical processes are disrupting the weakly bound string populations, leaving only individual clusters to be identified at the oldest ages. These data shed a new light on the local galactic structure and a large scale cloud collapse.

Rosetta at comet 67P: deciphering the origin of the solar system, the Earth and life

Main Colloquium
Prof. emer. Kathrin Altwegg
ORATED
Physikalisches Institut, Universität Bern, Switzerland

Although the Rosetta stone, found by the troops of Napoleon in Egypt near the city of Rosetta (Rashid) contains only a small amount of text in three languages it was key in deciphering Hieroglyphs. The Rosetta mission tried to achieve something similar: by looking at a tiny body its goal was to decipher the origin of the solar system, planets including Earth and life. After more than 12 years the Rosetta spacecraft softly crash-landed on comet Churyumov-Gerasimenko on September 30, 2016. It has traveled billions of kilometers, just to study a small (4 km diameter), black boulder named 67P/Churyumov-Gerasimenko. The results of this mission now seem to fully justify the time and money spent in the last decades on this endeavor. High resolution mass spectrometry in the near vicinity of the comet for more than two years revealed a huge amount of organics up to amino acids. The ROSINA (Rosetta Orbiter Sensor for Ion and Neutral Analysis) was able to identify many molecules and isotopologues, which let us reconstruct where these molecules must have formed and under which conditions. Three years after end of mission, we now have a good overview on the chemical composition of the nucleus, although data analysis is still ongoing and will need several more years to be completed. In this talk I will show how our perception changed on how the solar system formed thanks to Rosetta and especially ROSINA measurements.

Surveys of Low Mass Star Formation from the Millimeter to the IR

Main Colloquium
Prof. Tom Megeath
ORATED
University of Toledo, Ohio

Low mass stars constitute the majority of all stars formed, are the sites of planet formation, and trace star formation across diverse environments. Over the last 16 years, surveys with the Spitzer and Herschel telescopes have produced - for the first time - large, well characterized samples of low mass protostars; these objects directly trace the conversion of interstellar gas into low mass stars. I will discuss the next round of surveys of low mass protostars, including those in the radio with ALMA and VLA, in the mid-IR with Spitzer, and in the near-IR with HST. I will present three new results from these surveys: the identification of potentially the youngest protostars in Orion with ALMA and the VLA, a measurement of the rate of accretion driven outbursts utilizing a new Spitzer survey, and a study of the total mass accretion across a young cluster using the well characterized samples of protostars obtained with Spitzer and Herschel. Finally, I will briefly overview how this work can be further extended with JWST and with wide field near-IR surveys with the WFIRST telescope.

Atomic hydrogen in galaxies at intermediate redshifts

Special Colloquium
Apurba Bera
ORATED
National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India

Understanding the evolution of galaxies over cosmic time is one of the most important goals of modern astrophysics. In the recent past a number of deep optical studies of high redshift galaxies have provided information on the evolution of the stellar mass, star formation rate, luminosity function and morphological properties of the galaxy population. However, these studies provide no information about the evolution of the neutral atomic hydrogen (HI) content of galaxies. Since atomic hydrogen provides the primary reservoir of the material required for star formation, understanding its evolution is fundamental for understanding galaxy evolution. The atomic hydrogen content of galaxies is best probed by their HI-21cm emission. The upgraded Giant Metrewave Radio Telescope (uGMRT) with its band-5 (1.0-1.4 GHz) receivers is an excellent instrument to measure the HI-21cm emission from galaxies out to redshift of z < 0.4. We are carrying out a deep uGMRT observation of the Extended Groth Strip with the band-5 receivers to measure the HI content in star forming galaxies out to z < 0.4 in the field. In this talk I will present the first results from our observations.

Discovery of geometry transition in nearby AGN jets

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

Observational studies of collimation in jets in active galactic nuclei (AGN) are a key to understanding their formation and acceleration processes. We have performed an automated search for jet shape breaks in a sample of 367 AGN using VLBA data at 2 cm and 22 cm. This search has found ten nearby jets at redshifts z<0.07 with a transition from a parabolic to conical shape, while the full sample is dominated by distant AGN with a typical z=1. The ten AGN are UGC 00773, NGC 1052, 3C111, 3C120, TXS 0815-094, Mrk180, PKS 1514+00, NGC 6251, 3C371, and BL Lac. We conclude that the geometry transition may be a common effect in AGN jets. It can be observed only when sufficient linear resolution is obtained. Supplementing these results with previously reported shape breaks in the nearby AGN 1H 0323+342 and M87, we estimate that the break typically occurs at a distance of 105-106 gravitational radii from the nucleus. We suggest that the jet shape transition happens when the bulk plasma kinetic energy flux becomes equal to the Poynting energy flux, while the ambient medium pressure is assumed to be governed by Bondi accretion. Our model predictions on the jet acceleration and properties of the break point are found to be supported observationally.

Probing the Physical Conditions in the Prominent NGC 6334 North Star-forming Region with Multiple CO Transitions

Master Colloquium
Jana Schüller-Ruhl
ORATED
Max-Planck-Institut für Radioastronomie

NGC 6334 North is a prominent star-forming region. It consists of three different active sources. NGC 6334 I is a far-Infrared (FIR) source with active high mass star-formation. The source is associated with the ultra compact HII region F. NGC 6334 I(N) is a 1mm peak about 2' North of I. It is a dense cold core where high-mass star-formation is happening at an early evolutionary stage. The third source is the extended and shell-like HII region NGC 6334 E. In my thesis I used maps of different rotational transitions of 12CO, 13CO and C18O to probe the physical conditions of the molecular gas in and around those sources. The data were taken with the APEX telescope and the Herschel Space Observatory. The integrated intensity maps give a first idea of how the gas is distributed across the regions, establishing I as the brightest and I(N) as the faintest of the studied sources. Further analysis is conducted on the 13CO (3-2), (6-5), (8-7) and (10-9) lines. The computed line ratios and Spectral Line Energy Distributions (SLEDs) are compared to a variety of RADEX models to get an estimate of the parameters defining the physical conditions of the probed molecular gas. [Referees: Prof. Dr. Karl Menten, Prof. Dr. Pavel Kroupa]

Searches for fast radio transients in Parkes archival pulsar timing data

Master Colloquium
Aswin Manohar
ORATED
Max-Planck-Institut für Radioastronomie

Pulsars are a class of rapidly rotating, highly magnetized neutron star - the remnant of supernova explosions of massive stars - where the electromagnetic emission beams are visible as they sweep past the Earth. In general, pulsar surveys of the Galactic plane offer opportunities to scan a small fraction of the transient radio sky for bright millisecond duration bursts. The transient radio sky harbors many types of exotic objects and the recent discovery of Fast Radio Bursts (FRBs - bright millisecond duration bursts of high dispersion measure and extra-Galactic origin) and Rotating Radio Transients (RRATs - a new type of sparsely-emitting pulsar) has spurred renewed interest in the search for single-pulse emission. FRBs are powerful probes of the ionized inter-galactic medium and the properties of space-time itself. In this talk, I will describe the preliminary results from a search for transient radio bursts, and single pulses from pulsars, in Parkes archival pulsar timing data (from 1996 onwards). As well as one convincing FRB candidate, I will discuss the limitations of machine learning algorithms for detecting single pulses and present the pulse energy distributions of selected pulsars detected in the search. [Refeeres: Prof. Dr. Michael Kramer, Prof. Dr. Pavel Kroupa]

Exploring the F-GAMMA database: a blazar variability analysis in the emission frame

Lunch Colloquium
Dr. Nicola Marchili
ORATED
Istituto di Radioastronomia - INAF, Bologna, Italy

With more than 50 blazars monitored at 10 different frequencies (from 2.7 to 142 GHz) for about 8 years, the F-GAMMA Program provided us with an incomparable database to study the evolution of flares across the electromagnetic spectrum. To fully exploit the potentials of this unique archive, an advanced tool for the decomposition of light curves into flares has been developed, treating the data as three-dimensional arrays having time, frequency, and flux density as coordinates. We present here the main results of an in-depth time series analysis of the F-GAMMA database. To allow a comparison among different sources, the analysis has been extended to the emission frame. This approach comes not free of complications, but its ability to overcome the problem of boosting biases could represent a subtantial step forward for the comprehension of the blazar phenomenon.

Status of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav)

Main Colloquium
Dr. Timothy Pennucci
ORATED
Eötvös Loránd University, Institute of Physics, Budapest, Hungary

Supermassive black hole binaries, and possibly other sources, generate gravitational waves (GWs) at nanohertz frequencies. For almost a decade and a half, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the 100-m Green Bank Telescope, the 305-m Arecibo Observatory, and, more recently, the 27 × 25-m Very Large Array to observe an ensemble of millisecond pulsars (MSPs) in a pulsar timing array (PTA) experiment. I will present our current observational program of 76 MSPs, an overview of our newest, 12.5-year dataset, recent results from searches for GWs, and new analysis techniques that are designed specifically for the current and future generation of wideband pulsar instrumentation. These wideband methods are also more generally applicable to known-pulsar observations, with use-cases in the CHIME and MeerTime experiments, as well as the pulsar data collected from the Effelsberg telescope.

Optimizing digital spectrometers for radioastronomical observations

Master Colloquium
Gerrit Grutzeck
ORATED
Argelander-Institut für Astronomie

The goal of this thesis was to develop a procedure to optimize the mirror suppression, which reduces the dynamic range of the Fast Fourier Transform spectrometers (FFTS), and implement this procedure in the Field Programmable Gate Array (FPGA) of the FFTS. This is achieved by applying a calibration on the complex amplitude spectrum. The FFTS will be used as backends for the CCAT-prime Heterodyne Array Instrument (CHAI). Such multi-beam Heterodyne receivers are equipped with a large number of independent signal chains, which leads to a complex system that consumes space as well as power and is expensive. To reduce the complexity of the receiver array the intermediate frequency (IF) band is 4-8 GHz, which requires the FFTS to sample this band directly. The input bandwidth of 4 GHz of the current generation of FFTS cannot be sampled with a single analog-digital converter (ADC). To reach that bandwidth, multiple ADCs sample the same signal at different points in time. The method is called “time interleaved sampling”. The characteristics of the ADCs differ from each other, which leads to mirror signals in the spectrum. These mirror signals can reduce the dynamic range of the spectrometers. Therefore the mismatches must be actively corrected. The current generation of FFTS use a frequency independent calibration, which optimizes the mirror suppression at one fixed frequency. This is not optimal as some of the mismatches are frequency dependent and their impact increases with frequency. The procedure developed during this thesis work involves three steps. First the mismatches are measured over the frequency band. Then filter coefficients are calculated from these mismatches using a model of a time interleaved ADC. These filter coefficients are then applied to the complex amplitude spectra of the ADCs. The newly implemented calibration improves the mirror suppression up to 20 dB compared to the frequency independent calibration. [Referees: Prof. Dr. Frank Bertoldi, Prof. Dr. Bernd Klein]

Radio Continuum of Galaxies with H2O-Megamaser Disks

Promotionskolloquium
Fateme Kamali
ORATED
Max-Planck-Institut für Radioastronomie

Galaxies with H2O-megamaser disks are low luminosity active galaxies where 22 GHz H2O-maser emission is detected in their accretion disk surrounding the central supermassive black hole. Given that the geometry of the maser disk is known, these galaxies provide a unique view of the central region of active galaxies, allowing us to investigate the spatial relationship of the accretion disk with jets on the same physical scales. In order to carry out these investigations, we observed a sample (and later a sub-sample) of 24 H2O-megamaser-disk galaxies at 33 GHz and/or 5 GHz, using three different radio interferometer arrays with different resolutions which correspond to physical scales of sub-kpc to pc for our sources. Our observations provide a larger sample where morphology or geometry of both accretion disk and jets are observed on similar physical scales. We find out that the pc-scale radio continuum is misaligned relative to the rotation axis of the maser disk in four sources which exhibit both a radio continuum and maser disk with known orientation. However, the continuum orientations are not random, but are confined to a cone within 32 degree of the maser disk's normal, with a 99.1% confidence level. Among these four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the radio continuum luminosity and the maser disk's inner radius. We also conclude that the radio emission in the majority of our sources is dominated by both outflow and star formation, based on the spectral indices, brightness temperatures, and multi-scale morphologies. [Referees: Prof. Dr. Karl M. Menten, Prof. Dr. Pavel Kroupa, Prof. Dr. Simon Stellmer, Prof. Dr. Volkmar Gieselmann]

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 newly established group at the AIfA. While until the last few years extragalactic molecular gas surveys have been largely restricted to coarse inventories, 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 mm-wave, molecular lines, 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.

Probing the Magnetized Disk-Halo Transition Region of M51 using Wideband Polarimetry

Promotionskolloquium
Maja Kierdorf
ORATED
Max-Planck-Institut für Radioastronomie

During my PhD, I studied magnetic fields in the diffuse interstellar medium of a nearby galaxy and in polarized extragalactic point sources using wideband polarimetry, a powerful tool to reveal magnetic fields in different environments. In my talk, I will show the results of my study of the grand design face-on spiral galaxy M51 which is an excellent laboratory for studying magnetic fields in galaxies. I will present new observations of M51 with the Very Large Array at S-band (2-4GHz), where currently no polarization data exists to shed new light on the transition region between disk and halo. This critical frequency coverage also fills the gap of polarization observations between high and low radio frequencies, providing me with the widest frequency coverage (1-8GHz) polarization data set for a nearby face-on spiral galaxy to date. I compared the observed degree of polarization across 7 GHz with an analytical depolarization model. Since the model predictions strongly differ within the wavelength range of S-band, my new data are essential to distinguish between systems with different magnetic field configurations present in M51. I found reasonable parameters of the magneto-ionic medium in M51 which can fit the broadband polarization fraction across 1-8 GHz. This method is a promising tool for studying magnetic fields in galaxies which can be applied to other galaxies in the future and will highly improve our understanding of galactic magnetic fields. [Referees: Prof. Dr. Michael Kramer, Prof. Dr. Pavel Kroupa, Prof. Dr. Jochen Dingfelder, Prof. Dr. Barbara Kirchner]

Dispersal of giant molecular clouds by UV radiation feedback from massive stars

Special Colloquium
Dr. Jeong-Gyu Kim
ORATED
Princeton University, USA

UV radiation emitted by massive OB stars profoundly affects the evolution of giant molecular clouds (GMCs) by exciting H II regions and driving their expansion. UV radiation escaping from GMCs also plays a key role in regulating heating and ionization of the diffuse ISM. In this talk, I will present the results of radiation hydrodynamic simulations of cluster-forming turbulent clouds, focusing on cloud dispersal and escape of radiation. Our parameter study shows that the cloud destruction takes ~2-10 Myr after the onset of radiation feedback and that the final star formation efficiency increases primarily with the initial surface density of the cloud. Radiation pressure plays a greater role than photoionization in driving outflows and quenching star formation in high surface density clouds. A significant fraction (0.05-0.58) of ionizing and non-ionizing UV photons escape through large, low-density holes created by turbulence before the time of the first supernova. I will discuss implications of our results for observations, including inference of star formation efficiency in individual GMCs, and accounting for diffuse ionized gas on galactic scales.

The upgraded GMRT: Opening new windows to the Universe

Special Colloquium
Prof. Yashwant Gupta
ORATED
National Centre for Radio Astrophysics, India

The GMRT, a frontline low frequency radio observatory operational since 2002, has recently completed a major upgrade that is targeted to improve its sensitivity by a factor of upto three and make it a much more versatile instrument. This upgrade will keep the GMRT at the forefront as one of the most sensitive facility in the world in the 50 to 1500 MHz range, till the SKA phase I comes along. The upgraded GMRT (uGMRT) has been made available to users in a phased manner since mid-2016. The fully completed uGMRT was formally inaugurated in March 2019. Already several exciting new results are beginning to flow from the uGMRT. This talk will describe all this, and also bring out challenges faced and the plans for the future.

MHD disks and jets - simulations of the accretion-ejection structure

Main Colloquium
Dr. Christian Fendt
ORATED
MPIA Heidelberg

I will present recent MHD simulations investigating the launching of astrophysical jets. The simulations treat the time-dependent evolution of the accretion-ejection structure and the subsequent collimation of the disk wind into a high-velocity jet. I will discuss simulations considering (i) a mean-field accretion disk dynamo and the launching of outflows by a self-generated disk magnetic field, (ii) a general interrelation between the disk magnetization and the jet dynamics, and (iii) relativistic jet launching.

The Global Star Formation Laws in Galaxies

Special Colloquium
Prof. Yu Gao
ORATED
Purple Mountain Observatory

The dense molecular gas mass, traced by HCN J = 1-0, correlates linearly with the far-infrared (FIR) luminosity (star formation rate, SFR) for essentially all star-forming systems near and far. The spatially resolved FIR-HCN correlation in the disks of spiral galaxies, a local star formation law in terms of dense molecular gas across the spiral disks, appears also to be linear and is essentially the same as that established globally from the Galactic dense molecular cloud cores and the galaxies. And this linear correlation is valid for all other dense molecular gas tracers, e.g., CS, HCO+ and high-J CO. Such linear correlations suggest that the SFR depends linearly upon the mass of dense molecular gas. This is drastically different from the traditionally established Kennicutt-Schmidt (K-S) laws that relate the total gas to SFR in galaxies since there is no unique correlation in these K-S laws. Finally, we introduce the first results of the MALATANG large program on the JCMT to map the HCN and HCO+ J = 4 - 3 line emission in 20 nearest and FIR-brightest galaxies. MALATANG bridges the gap, in terms of physical scale and luminosity, between extragalactic (i.e., galaxy-integrated) and Galactic (i.e., giant molecular clouds) observations, showing again such linear correlation in FIR - high-J HCN/HCO+ emission.

The relation between star formation and ram pressure in jellyfish galaxies

Lunch Colloquium
Ms. Iveth Gaspar-Gorostieta
ORATED
Instituto de Radioastronomia y Astrofisica (IRyA, UNAM)

I will present the analysis of the stellar population properties in a sample of the so-called jellyfish galaxies observed with MUSE@VLT in the frame of the GASP project. These galaxies take their name from the morphological resemblance to jellyfishes, displaying long tails of gas and newly born stars provoked by the interaction, via ram pressure stripping, between the hot intracluster medium and the gas with the galaxy itself. According to numerical simulations, ram pressure has a double effect: firstly, by compressing the gas within the galaxy, it might provoque an enhancement of the star formation activity, which can lead to an increment in the star formation rate within the galactic disk by up to a factor of 3-5. Later on in the interaction, ram pressure will push the gas that was once inside the galactic disk away, creating long (up to ~80 kpc) tails where star formation can occur. The aim of my work is to study the relation between the “enhanced” star formation activity, and the properties of both the galaxy (stellar mass, morphology, gas content, position within the cluster, velocity) and the cluster it is accreting onto.

The Many Faces of the SZ Effect

Special Colloquium
Dr. Kaustuv Basu
ORATED
AIfA

The Sunyaev-Zeldovich (SZ) effect was first proposed in the 1970s as a means to identify the X-ray emitting hot electron plasma inside massive clusters of galaxies and obtain the cluster velocities relative to the cosmic microwave background. Yet, it is only within the last decade that is has begun to significantly impact astronomical research. I will describe the five distinct flavours and unique diagnostic characteristics of the SZ effect, and outline our group's research aiming to unlock some of its future applications. Specifically, I will show how the SZ effect can be complementary to multiple research topics in optical, radio, and X-ray astronomy, which are pursued strongly in Bonn. As an outlook, I will mention CCAT-prime, a novel submillimeter telescope we are building in Chile to advance the next level of SZ science.

Tracing Galactic magnetic fields with diffuse radio polarisation

Special Colloquium
Alec Thomson
ORATED
Australian National University

Magnetic fields pervade the interstellar medium (ISM) of galaxies. These fields lock into the ionised phases of the ISM, forming the magneto-ionic medium, and provide significant inputs of energy. By studying the magnetic properties of the Milky Way we are able to study the interactions between components of the ISM in the greatest detail. I will present results from observations of diffuse polarised radio emissions, made with the Parkes 64m telescope. Specifically, I will discuss using the S-band Polarisation All Sky Survey (S-PASS) and the Global Magneto-Ionic Medium Survey (GMIMS) to trace magneto-ionic structures. As the Galaxy itself is a significant source of polarised emission, the diffuse polarised radio sky is rich in information on the Galactic magnetic field across large angular scales.

Pulsar Searching and Timing with the Arecibo and Effelsberg Radio Telescopes

Promotionskolloquium
Jose Martinez
ORATED
Max-Planck-Institut für Radioastronomie

Pulsars are rapidly rotating, highly magnetized, neutron star remnants of the supernova explosions of massive stars. In this talk, I will mostly focus on recycled pulsars, which are old (~10^{8} yr) neutron stars that are descendants from close, interacting binary systems. They have extraordinary rotational stability due to being spun-up (recycled) to fast spin periods (few to tenths of milliseconds) by accretion of mass and angular momentum from their companion star. Their extreme properties have made them fundamental tools for a broad range of applications, including the study of ultra-dense matter, the tests of relativistic theories of gravity, and the search for low-frequency gravitational waves. I will present the discovery and follow-up of PSR J0453+1559 and PSR J1411+2551, which both are double neutron star systems (DNS). DNS are rare systems of which two massive stars orbit each other their entire life and survived each other's explosive supernova deaths leaving behind two neutron stars in an eccentric orbit. PSR J0453+1559 is the first asymmetric DNS that has a pulsar mass of 1.559(5) solar masses and the mass of the companion is 1.174(4) solar masses, the lightest precise neutron star mass measurement as of today. PSR~J1411+2551 is among one of the lightest total mass systems from all the known DNS population, that could leave behind a massive neutron star after its merger event. Additionally, I will present 6 recycled pulsars, five which are in a binary and one isolated millisecond pulsar. [Referees: Prof. Dr. Michael Kramer, Prof. Dr. Norbert Langer, Prof. Dr. Klaus Desch, Prof. Dr. Andreas Bott]

Complex organic chemistry in high-mass star-forming regions

Promotionskolloquium
Mélisse Bonfand
ORATED
Max-Planck-Institut für Radioastronomie

The quest for interstellar complex organic molecules (COMs) lies at the heart of astrochemistry with the aim to understand which conditions are required to establish chemical complexity in the interstellar medium (ISM) and to figure out which degree of complexity can be reached. Most interstellar COMs were first detected toward the compact, dense, and warm parts of high-mass star-forming regions, called hot molecular cores. In particular, the Galactic center molecular cloud Sagittarius B2 (Sgr B2), one of the most active star-forming regions in our Galaxy, is an excellent target to search for COMs and probe the ISM complex chemistry under extreme physical conditions (high densities, high temperatures, strong radiation field, high cosmic-ray flux). In my thesis I took advantage of the high sensitivity of the imaging spectral line survey EMoCA conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) to study the spatial structure and chemical content of active star-forming regions in Sgr B2. The analysis revealed the presence of three new hot cores in Sgr B2(N), one of Sgr B2's main star-forming sites. I will present the results of a detailed comparative study of the hot cores' chemical composition, physical properties, spatial structure, and evolutionary stage. The derived physical properties are used to investigate the time-dependent chemical evolution of the hot cores with astrochemical models. The resulting chemical abundances are compared to the observed ones to constrain the interstellar radiation field strength, the minimum dust temperature during the prestellar phase, and the cosmic-ray ionization rate that best characterize Sgr B2(N). [Referees: Prof. Dr. Karl M. Menten, Prof. Dr. Pavel Kroupa, Prof. Dr. Klaus Desch, Prof. Dr. Hubert Schorle]

Magnetic fields in neutron stars: from radio pulsars to magnetars

Main Colloquium
Dr. Nanda Rea
ORATED
Institute of Space Sciences, Barcelona

I will review current observational and modelling results on neutron stars with strong magnetic fields (aka magnetars): in particular their outburst activity, their predicted evolution, birth, and possible connection with GRBs and SLSNe. Furthermore, I will present new discoveries that strengthen somehow the relation between magnetars and other neutron star classes, and that argue on the ubiquitous presence of strong field non-dipolar component in possibly any young neutron star.

TBD

Main Colloquium
Dr. Francisco Colomer
CANCELED
Joint Institute for VLBI ERIC (JIVE), Dwingeloo, the Netherlands

TBD

Constraining redshifts of fast radio transients with (and without) e-MERLIN

Special Colloquium
Dr. Charles Walker
ORATED
University of Manchester, UK

Pulsars, discovered in 1986, Rotating Radio Transients (RRATs), initially reported in 2005, and Fast Radio Bursts (FRBs), first detected in 2007 are all sources of short-duration radio emission and examples of fast radio transient phenomena. Due to the propagation effects experienced by such signals, they may be used as probes of the intervening environments between us and their sources. Not least among these propagation effects is the dispersion experienced by radio waves as they pass through ionised environments. By using dispersion pulsars have been used to model the electron distribution of the Milky Way; using similar techniques, a population of extragalactic FRBs could be used to probe environments beyond our own Galaxy. Using the observed dispersion measures (DMs) of FRBs as a proxy for intervening matter and thus distance, astronomers are already estimating the distances to sources. The components contributing to the DMs of extragalactic bursts, however, consist of many component. These contributions, from the intergalactic medium (IGM), host galaxy, and local burst environment are dependent on their source redshifts, relativistic effects such as cosmological time dilation and host galaxy recession, and ultimately, the progenitors of FRBs themselves. Analysis of these components is thus non-trivial, and so the optimal way of obtaining the redshifts of FRBs remains localising them to host galaxies using the fine angular resolutions of radio interferometers. In this talk I shall overview the work undertaken during my PhD, including developing a high time-resolution backend for the UK's e-MERLIN interferometer for the detection and localisation of fast transient phenomena; and developing a statistical framework for studying the relationship between the source redshifts and dispersion measures of extragalactic transients, in order to better estimate the redshifts of poorly localised events, and to identify potential uses for large numbers of localized FRBs when they are eventually accumulated.

High-energy neutrino astronomy and radio-loud active galactic nuclei: current status and prospectives

Lunch Colloquium
Dr. Emma Kun
ORATED
University of Szeged, Hungary

The central supermassive black hole of the radio-loud active galactic nuclei (AGN) launches a pair of relativistic jets from its immediate vicinity. Cosmic ray observations demonstrated that AGN jets are the most powerful particle accelerators in the universe, allowing exotic particle processes to occur in them. Although cosmic rays, neutrinos and gamma-photons are intimately related, neutrinos are the only messengers we can observe from the distant corners of the universe, where AGN activity was already present. While the small number of the direct detections of high-energy neutrinos coming from radio-loud AGN does not enable yet statistical studies about the significance of their connection, more and more observational results suggest radio-loud AGN might be indeed prominent sources of high-energy neutrinos, as predicted by theoretical studies. In my talk I will review what we know about those radio-loud AGN that emerged as candidates to be the origin of high-energy neutrinos detected by the IceCube South Pole Neutrino Observatory and I will review the most important questions to answer concerning this field.

Hearing the 3D shape of Musca molecular cloud

Main Colloquium
Prof. Konstantinos Tassis
ORATED
Department of Physics, University of Crete and Institute of Astronomy, FORTH, Greece

Dust continuum and molecular observations of the low column density parts of molecular clouds have revealed the presence of elongated structures which appear to be well aligned with the magnetic field. These so-called striations are remarkably ordered structures in otherwise chaotic-looking clouds. They encode information revealing the properties of their parent clouds. We have demonstrated that magnetosonic waves, ubiquitous in molecular clouds, are the most probable cause of striations, since they are the only mechanism that can reproduce quantitatively their observed properties. If indeed striations are the interstellar ripples caused by the passage of magnetosonic waves, then profound consequences are implied for their ability to reveal hidden, important information about molecular clouds. I will present a specific example: striations in the Musca molecular cloud are found to encode normal modes of the cloud's global magnetosonic vibrations, allowing the reconstruction of its 3D shape.

Enabling charge particle astronomy with Galactic magnetic tomography

Lunch Colloquium
Dr. Vasiliki Pavlidou
ORATED
Department of Physics, University of Crete

The sources of the highest-energy particles in the Universe remain an unresolved mystery. The reason is that charged-particle astronomy is severely complicated by magnetic deflections. I will discuss a radically new approach to charged-particle astronomy: constructing a 3-dimensional map of local Galactic magnetic field measurements, primarily through optopolarimetric magnetic tomography, and backtracking the paths that UHECR traverse through the Galaxy before reaching us, to improve agreement between their (corrected) arrival directions and the location of their sources on the sky. Effectively, this technique aims to improve the charged-particle point-spread-function by a factor of several, boosting the sensitivity to individual sources by a similar factor, and allowing us to probe the cosmic-ray composition at the highest energies without reference to the development of extensive air showers in the atmosphere. This approach is becoming possible for the first time thanks to two experimental breakthroughs: the unparalleled wealth of stellar distances that the Gaia mission is in the process of providing; and recent advances in optopolarimetry of point sources that make possible systematic large-area surveys of stars. This technique would act multiplicatively on the return from current and future cosmic-ray observatories, ground- and space-based.

HCN emission in circumstellar envelopes of carbon-rich AGB stars

Master Colloquium
Manali Jeste
ORATED
Max-Planck-Institut für Radioastronomie

Low- and intermediate-mass stars, after moving past the Horizontal Branch in the Hertzsprung-Russell diagram, reach the Asymptotic Giant Branch (AGB) where they start the final parts of their lives. AGB objects have a carbon-oxygen core at the center of helium- and hydrogen-burning shells and are surrounded by a circumstellar envelope (CSE). The star becomes carbon-rich when the abundance ratio of carbon to oxygen, C/O, becomes higher than 1 due to the third dredge-up mechanism. AGB stars contribute substantially to the molecular enrichment of the interstellar medium. HCN is one of the most abundant carbon-bearing molecules found in the atmospheres and CSEs of these stars. For this study, we observed a total of 16 carbon-rich AGB stars using the APEX telescope in the J = 2-1 to 4-3 transitions of HCN and combined this data set with archival Herschel telescope data (J = 6-5 to 13-12 transitions). In addition to lines from the ground state, we detected rotational lines from various vibrationally excited levels of HCN, which trace the innermost hot regions of the CSE. Until now, the only AGB star for which such multi-transition HCN data sets have been discussed is the nearby, high mass-loss object IRC+10216. We have analyzed the HCN data for all the 16 sources and investigated the excitation conditions (temperature and column densities) in detail, for 3 of them, namely CRL-3068, II Lup, and IRC+10216. In the future, we plan to model HCN emission in AGB stars by combining our data with spatial information obtained with ALMA. [Referees: Prof. Karl Menten, Prof. Pavel Kroupa]

Finding Cosmic Inflation

Main Colloquium
Prof. Eiichiro Komatsu
ORATED
Max-Planck-Institut für Astrophysik, Garching

The cosmic microwave background (CMB) research told us a remarkable story: the structure we see in our Universe such as galaxies, stars, planets, and eventually ourselves originated from tiny quantum fluctuations generated in the early Universe. With the WMAP we have confirmed many of the key predictions of inflation including flatness and statistical homogeneity of our Universe, Gaussianity and adiabaticity of primordial density fluctuations, and a small but non-zero deviation from the scale-invariant spectrum of density fluctuations. Yet, the extraordinary claim requires extraordinary evidence. The last prediction of inflation that is yet to be confirmed is the existence of primordial gravitational waves whose wavelength can be as big as billions of light years. To this end we have proposed to JAXA a new satellite mission called LiteBIRD, whose primary scientific goal is to find signatures of gravitational waves in the polarisation of the CMB. In this presentation we describe the current state of affairs regarding our understanding of the early Universe, physics of polarisation of CMB, the LiteBIRD proposal, as well as a sub-mm telescope in Chile called CCAT-p that we are currently building.

Hybrid Imaging/Periodicity Search for Pulsars

Master Colloquium
Aakash Mantri
ORATED
Max-Planck-Institut für Radioastronomie

Pulsars are rapidly rotating compact stellar remnants with extreme surface gravity and magnetic fields. By virtue of their extraordinarily predictable rotation, pulsars have been used as astrophysical laboratories for strong-field gravity and the detection of gravitational waves. Until now, ~ 2,700 pulsars out of the predicted 30,000 pulsars have been discovered in our Milky way. I will present Hybrid Imaging/Periodicity Search technique which identifies compact sources in the radio continuum images, and rank pulsar candidates based on spectral, polarization, variability, and multi wavelength characteristics. Radio continuum surveys are equally sensitive to all pulsars, not affected by dispersion measure smearing, scattering or orbital modulation of spin periods. This allows us to search for extreme pulsars, such as sub-millisecond pulsars, pulsar-black hole systems and pulsars in the Galactic Center. As we enter the Square Kilometer Array (SKA) era, searching for pulsars in continuum images will complement traditional pulsar searches, and make it possible to find extreme objects. [Referees: Prof. Michael Kramer, Prof. Nobert Langer]

Radio Recombination Lines of HII regions with the Galactic plane survey GLOSTAR in a Galactic longitude range between 23 deg and 28 deg

Master Colloquium
Daniel Ott
ORATED
Max-Planck-Institut für Radioastronomie

In this work HII regions are searched for in the Galactic zone 23 deg <= l <= 28 deg with |b| <= 1 deg. Those regions are identified as HII regions with RRL emission. This emission is obtained as part of the GLOSTAR survey at the Karl Jansky Very Large Array (JVLA) in a frequency range of 4.2-5.2 GHz and 6.4-7.4 GHz. The RRL data is calibrated and imaged. The 103 targets are selected based on NVSS objects spatially coincident with MIR emissions. 68 (66%) HII regions are confirmed in the RRL images. The velocity, line width and flux density are measured. Based on velocity and Galactic position the Galactocentric and heliocentric distance of the confirmed HII regions is derived. The line-to-continuum ratio based on the integrated GLOSTAR continuum flux densities is determined and investigated. The velocities and distances are compared to other existing catalogs. [Referees: Prof. Dr. Karl Menten, Priv. Doz. Dr. Maria Massi]

Magnets in the Sky

Main Colloquium
Prof. Bryan Gaensler
ORATED
Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Canada

Everywhere we look, the Universe is threaded with magnetism. These magnetic fields are surprisingly organised and coherent, and are vital to many of the fundamental processes that astronomers take for granted. However, the mechanisms that create and then sustain magnetism in the Universe are not understood, in no small part because magnetic fields are usually not directly observable. I will present innovative new observations of radio polarimetry and Faraday rotation, and will explain how these data sets provide a unique view of magnetic fields in the Milky Way, in distant galaxies, and in the intergalactic medium. I will conclude by showcasing the powerful new generation of radio telescopes that are at last fully opening the window to the magnetic Universe.

The subsurface ocean of Enceladus: A habitable place in our solar system ?

Main Colloquium
Prof. Frank Postberg
ORATED
Institute of Geological Sciences, Freie Universität Berlin

Saturn's icy moon Enceladus harbours a global ocean, which lies under an ice crust of just a few kilometres thickness and above a rocky core. Through warm cracks in the crust a cryo-volcanic plume ejects ice grains and vapour into space providing access to materials originating from the ocean. The ocean is 30-55 km deep and provides an environment of mild salinity and alkaline pH. Hydrothermal activity is suspected to be occurring at the bottom of the ocean and also deep inside the water-percolated porous core. The energy is delivered by tidal dissipation. Two mass spectrometers aboard the Cassini spacecraft, the Cosmic Dust Analyzer (CDA) and the Ion and Neutral Gas Spectrometer (INMS) frequently carried out compositional in situ measurements of plume material emerging from the subsurface of Enceladus. Our latest results now show that, in addition to volatile organic compounds, some emitted ice grains contain concentrated macromolecular organic material with molecular masses clearly above 200u. The mass spectra of the two instruments provide key constraints on the macromolecular structure that contains both aromatic and aliphatic constituents as well as oxygen bearing and likely nitrogen bearing functional groups. The finding is suggestive of thin organic-rich film on top of the oceanic water surface. We suggest that the detected organic compounds mostly originate from Enceladus' hydrothermally active rocky core. Thermal ocean convection together with bubbles of volatile gases, transports these and other materials from the moon's core up to the ocean surface. There, organic nucleation cores - generated by bubble bursting and subsequently coated with ice from vapor freezing - are ejected into space. This nucleation shows similarities to the formation of ice clouds from organic sea spray on Earth and allows probing of Enceladus' organic inventory in drastically enhanced concentrations.

Live from Brussels: First Results of the Event Horizon Telescope

Special Colloquium
Various Panelists
ORATED
Event Horizon Telescope Collaboration

Live streaming from the press conference in Brussels to present a groundbreaking result from the Event Horizon Telescope. The press conference will be held at the Berlaymont Building of the European Commission in Brussels. The event will be introduced by European Commissioner for Research, Science and Innovation, Carlos Moedas, and will feature presentations by the researchers behind this result. Anton Zensus, Chair of the EHT Collaboration Board will also make remarks and introduce a panel of EHT researchers who will explain the result and answer questions: - Heino Falcke, Radboud University, Nijmegen, The Netherlands (Chair of the EHT Science Council) - Monika Mościbrodzka, Radboud University, Nijmegen, The Netherlands (EHT Working Group Coordinator) - Luciano Rezzolla, Goethe Universität, Frankfurt, Germany (EHT Board Member) - Eduardo Ros, Max-Planck-Institut für Radioastronomie, Bonn, Germany, (EHT Board Secretary) A total of six major press conferences will be held simultaneously around the globe in Brussels (English), Santiago de Chile (Spanish), Shanghai (Mandarin), Taipei (Mandarin), Tokyo (Japanese), and Washington, D.C. (English). The link to the streaming channel of the Brussels event is https://youtu.be/Dr20f19czeE

Characterizing the dense gas in galaxies

Main Colloquium
Prof. Serena Viti
ORATED
Dept of Physics and Astronomy, University College London, UK

It is now well established that chemistry in our Milky Way as well as in external galaxies is rich and complex. In this talk I will give an overview of the field of Astrochemistry, with special emphasis on its relevance to extragalactic studies. I will show how molecules play a key role in the formation and shaping of galaxies. By using examples from different regions of space, from interstellar and star forming gas, to gas surrounding AGNs, I will demonstrate how important molecules are for our understanding of star and galaxy formation. Finally I will present a new approach for the interpretation of molecules using Bayesian and Machine Learning techniques.

Massive filamentary clouds and their role in star formation

Promotionskolloquium
Michael Mattern
ORATED
Max-Planck-Institut für Radioastronomie

Filamentary structures are ubiquitous in the interstellar medium of the Milky Way. They are observed within star-forming and quiescent molecular clouds and representing molecular clouds themselves. Therefore, filamentary structures play an important role in the early phases of star formation. Filaments in nearby (closer than 500 pc) molecular clouds were found to be thermally stable against gravitational collapse, fragmenting into star-forming clumps. However, the evolution of filaments with masses above the thermally critical value is unknown. Here, I will present the analyzes of the kinematics of 283 filamentary molecular cloud candidates in the Galactic Plane using the 13CO(2–1) and C18O(2–1) data of the SEDIGISM (Structure, Excitation, and Dynamics of the Inner Galactic Inter Stellar Medium) survey. To do so, we developed an automated algorithm to derive size, mass, and kinematic properties towards all candidates. We find two-third of the filament candidates are coherent structures. Also, we find a correlation between the mass per unit length and the velocity dispersion of the filament. Further, I present the fragmentation characteristics and kinematics of the extremely long, massive Nessie filament. The fragmentation characteristics are derived from a combined near- and mid-infrared dust extinction map, and then compared with predictions from gravitational fragmentation models. We find that the characteristics of the fragments at all scales are similar to the predictions of one model. The kinematics provided by the SEDIGISM survey reveal Nessie as a single physical object, despite several morphological differences along the filament. [Referees: Prof. Dr. Karl M. Menten, Prof. Dr. Pavel Kroupa, Prof. Dr. Simon Stellmer, PD Dr. Ines Gütgemann]

Pulsar Searching with the Effelsberg Telescope

Promotionskolloquium
Marina Berezina
ORATED
Max-Planck-Institut für Radioastronomie

Pulsars, highly magnetised rapidly-rotating neutron stars, have proved themselves to be incredible tools for exploring many aspects of fundamental physics and astrophysics. More opportunities for building new theories and challenging the existing ones come with new discoveries, hence, are determined by the success of pulsar surveys. Here, I will report on the progress of an ambitious searching project, the Northern High Time Resolution Universe survey (HTRU-North) for pulsars and fast transients conducted with the Effelsberg telescope. In particular, I will present the study of the medium Galactic latitudes (mid-lat:|b| < 15 deg), including the low Galactic latitudes (low-lat:|b| < 3.5 deg), scanned in a 3-minute integration regime. With more than 1100 telescope-hours spent on source during the timescale of this thesis, 41% of the total number of mid-lat pointings were observed and processed with the quick-look pipeline, bringing the overall HTRU-North mid-lat coverage to 50.5%. I will demonstrate that the obtained data not only allowed us to make fifteen new pulsar discoveries, including two millisecond binary (MSP) pulsars, but this data set (and the hundreds of known pulsar redetections that it includes) also became useful material for the analysis of the HTRU-North sensitivity, leading to a strategy revision for the next stages of the survey. Speaking about the HTRU-North discoveries, I will also present the results of the timing study of the two new binaries, PSR J2045+3633 and PSR J2053+4650. Due to their favourable orbital configurations – a relatively large eccentricity of PSR J2045+3633 (e = 0.017) and a nearly edge-on position of PSR J2053+4650 – they both have a great potential for precise mass measurements necessary for putting constraints on the equation of state of high density matter. [Referees: Prof. Dr. Michael Kramer, Prof. Dr. Norbert Langer, Prof. Dr. Jochen Dingfelder, Prof. Dr. Robert Glaum]

The nuclear star cluster at the Galactic centre

Main Colloquium
Dr. Rainer Schödel
ORATED
Instituto de Astrofísica de Andalucía - CSIC, Granada, Spain

Sagittarius A\*, the Milky Way's central four million solar mass black hole, is surrounded by a star cluster of roughly 25 million solar masses. This cluster appears to be similar to the nuclear clusters that are observed in the majority of galaxies. In this talk I will review our current knowledge about the nuclear cluster of the Milky Way and present some yet unpublished results. Our analysis of the star formation history excludes a quasi-continuous star formation and shows that the cluster is mostly very old (~10 Gyr) and metal rich (about twice solar), which gives us some clues as to its formation. A few percent of its mass formed in the last ~300 Myr. There appears to exist the predicted stellar density cusp around Sagittarius A*, which is of great relevance for the potential future detection of extreme mass ratio inspiral events from similar systems by space-based gravitational wave observatories.

The first Large Survey Project observations with MeerKAT

Special Colloquium
Dr. Ian Heywood
CANCELED
University of Oxford, UK

MeerKAT is a 64-element radio interferometer, and is the South African precursor to the mid-frequency component of the Square Kilometre Array. Officially inaugurated in July of last year, observations have already begunfor two of its Large Survey Projects. These are ThunderKAT, which aims tostudy explosive and accretion-powered transient phenomena, and MIGHTEE which will use deep radio continuum, polarisation and spectral-line measurements to study galaxy evolution across the history of the Universe. In this talk I will provide an overview of MeerKAT, some of the first results from MIGHTEE and ThunderKAT, and describe some of the data processing challenges.

MeerKAT calibration and imaging challenges (when luxury problems attack)

Main Colloquium
Prof. Oleg Smirnov
ORATED
Rhodes University, Grahamstown, South Africa

I will present some early images obtained with the MeerKAT radio telescope, and discuss the calibration and imaging challenges posed by the instrument. The combination of exceptional L-band sensitivity and abundance of short spacings has already made for some spectacular radio maps, revealing faint extended structure in exquisite detail. At the same time, such an embarrassment of morphological detail pushes at the limitations of conventional CLEAN-based deconvolution techniques. I will present observations that highlight these limitations, and discuss emerging deconvolution techniques that could potentially alleviate such problems. I will also discuss the sheer data size challenge of MeerKAT, and look at computing approaches and techniques for dealing with them.

Advances in US Radio Astronomy: The Next Generation Very Large Array

Special Colloquium
Dr. Tony Beasley
ORATED
NRAO, USA

This talk will describe the current science goals, design and planning status of a future large centimeter radio array: the Next Generation Very Large Array (ngVLA). The ngVLA core will be located in the desert southwest of the United States and northern Mexico, and include the sites currently associated with the Very Long Baseline Array. ngVLA will open a new window on the Universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcsecond resolutions, and broadband continuum polarimetric imaging of non-thermal processes. With this array, many new frontiers in modern astronomy can be reached, including direct imaging and chemical analysis of planet formation in the terrestrial-zone or nearby stars, to studies of dust-obscured star formation and the cosmic baryon cycle down to pc-scales in the local Universe, detailed imaging of molecular gas and galaxy formation out to high redshifts, and high-resolution polarimetric studies of jets and other phenomena arising from interactions between stellar-mass/supermassive black holes and their environments. The current design for the ngVLA includes 10x more effective collecting area and 10x higher linear spatial resolution than the current JVLA or ALMA, carefully optimized for operation in the frequency range 10 GHz to 50 GHz, while simultaneously delivering world-leading sensitivity over the entire 1.2 GHz to 116 GHz spectrum. Scientific collaboration between ngVLA and ALMA/SKA1 is anticipated in coming decades, and discussions with potential international project partners are underway. NSF support of formal design and development activities is ongoing, enabling concept development and technology prototyping/risk reduction activities during the U.S astronomy Decadal Survey process. Configuration and site selection activities throughout New Mexico, Arizona, Western Texas and Mexico are in progress, antenna prototyping and hardware prototyping will commence within the next 18 months, and array construction is planned to begin in 2024/2025.

IRAM Status, Developments and Plans - Breaking the path for Modern Millimetre Astronomy

Main Colloquium
Dr. Karl Schuster
ORATED
IRAM, Grenoble

In 2019 IRAM will celebrate 40 years of existence and service to the astronomical community. Ever since the foundation of IRAM, operational and instrumental upgrades have kept IRAM at the forefront of millimetre wave astronomy. Over the last years IRAMs facilities NOEMA and the 30m telescope once more underwent rapid evolution and upgrades on all levels. I will describe the recent status of the observatories and the resulting scientific capabilities. While the upgrades provide vastly improved return for well-established science topics they also open up totally new approaches of astronomical research. In a second part I will explain the challenges of the next steps as well as outline the ongoing developments and the current plans for the future of the IRAM facilities.

Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to the Galactic Centre

Promotionskolloquium
Vivien Thiel
ORATED
Max-Planck-Institut für Radioastronomie

Diffuse and translucent molecular clouds constitute a large part of the molecular interstellar medium (ISM) in our Galaxy as well as in other spiral galaxies. In particular, the envelopes of giant molecular clouds (GMCs), which host star forming regions, consist of lower density diffuse and translucent media. Hence, observational studies of diffuse and translucent molecular clouds help to improve our knowledge about their important role in the formation of dense clouds and their interaction with the rest of the ISM. For this project, we used absorption data from various molecules extracted from the EMoCA interferometric spectral line survey performed with ALMA towards the prominent GMC Sagittarius B2 (Sgr B2). The absorption spectra trace clouds along the whole line of sight (l.o.s.) to Sgr B2. We investigated the chemical content towards a selected sample of positions. We analysed the velocity structure of the absorption spectra and searched for correlations between molecules. We identified two groups of correlated molecules, with one group likely tracing shocked gas and the other one quiescent components. On the basis of HCO+, we conclude that most l.o.s. molecular clouds towards Sgr B2 are translucent. Our investigation of the spatial structure of the clouds seen in absorption in front of the extended continuum structure of Sgr B2(N) indicates that they are relatively homogeneous on scales smaller than the extent of the background continuum source. In addition, we report the detection of four complex organic molecules (COMs) in clouds of the Galactic Centre region and of two COMs in the translucent clouds associated with the Scutum arm of the Galaxy. [Referees: Prof. Dr. Karl M. Menten, Prof. Dr. Pavel Kroupa, Prof. Dr. Ian Brock, Prof. Dr. Hubert Schorle]

Relativistic Jets as Probes of Dark Matter, Galaxy Formation, and Supermassive Black Holes

Special Colloquium
Prof. Anthony Readhead
ORATED
California Institute of Technology, Pasadena, CA, U.S.A.

It might be imagined that after six decades of intensive study, the big astrophysical and cosmological questions related to Relativistic Jets (RJ) have all been answered, and that RJ studies are now relegated to answering second-order questions, but this is decidedly not the case. The zeroth order questions RJ studies have answered in the past, involving cosmological models, cosmological evolution, unified theories, and dark matter will be briefly reviewed. It will then be argued that we have now entered a new era in which RJ studies are again taking center stage due to recent and imminent astrophysical and technical advances, some of which have been spearheaded by the MPIfR. These provide opportunities for both traditional and novel RJ lines of attack on both old and new zeroth order questions: in fundamental physics, in cosmology, and in astrophysics - some of which will be answered over the next five years and some over the next decade and a half.

The role of interstellar and local cosmic rays on Galactic star formation

Main Colloquium
Dr. Marco Padovani
ORATED
INAF, Osservatorio Astrofisico di Arcetri, Italy

The study of the interaction of cosmic rays with the interstellar matteris a multi-disciplinary investigation that involves the analysis of several physical and chemical processes: ionisation of atomic and molecular hydrogen, energy loss by elastic and inelastic collisions, energy deposition by primary and secondary electrons, gamma-ray production by pion decay, the production of light elements by spallation reactions, and much more. Cosmic-ray ionisation activates the rich chemistry of dense molecular clouds and determines the degree of coupling of the gas with the local magnetic field, which in turn controls the collapse timescale and thestar-formation efficiency of a molecular cloud. In recent years a wealthof observations from the ground and from space has provided information and constraints that still need to be incorporated in a consistent global theoretical framework. My goal is to use the results of chemical models and state-of-the-art numerical simulations supplemented by dedicated observations to provide a unifying interpretation of the data with a model of cosmic-ray propagation specifically developed to make predictions that can be tested against the observations. I will also introduce a mechanism able to locally accelerate cosmic rays in protostars that can be used to explain the high ionization rate as well as the synchrotron emission observed towards protostellar sources. Finally, I will talk about my most recent study focused on the capability of SKA in detecting synchrotron emission in molecular cloud cores.

Plasma simulator

Special Colloquium
Dr. Alexander (Sasha) Philippov
ORATED
Center for Computational Astrophysics, Flatiron Institute, New York, USA

The modeling of pulsar radio and gamma-ray emission suggests that in order to interpret the observations one needs to understand the field geometry and the plasma state in the emission region. To understand this from first principles, we constructed global kinetic simulations of pulsar magnetospheres using relativistic Particle-in-Cell codes, which capture the physics of plasma production and particle acceleration. In this talk I will present modeling of high-energy light curves, calculated self-consistently from particle motion in the pulsar magnetosphere. I will also show evidence that "usual" radio emission is powered by non-stationary discharge at the polar cap, while the radio emission from the outer magnetosphere is produced by plasmoid mergers in the current sheet beyond the light cylinder.

Non-thermal Excitation of Atomic and Molecular Lines

Lunch Colloquium
Dr. Thomas L. Wilson
ORATED
Max-Planck-Institut für Radioastronomie

In the radio range, observations show that there are deviations from Local Thermodynamic Equilibrium (LTE) in a number of atomic and molecular species. These deviations can be large, that is, the so-called strong maser lines of OH, water vapor, methanol and SiO. There are other situations in which the deviations are small, so the measurements are not so definite. Among these are the radio recombination lines of hydrogen and carbon. A discussion based on the history of measurements and interpretations is presented to provide a general explanation of maser action and a few specific examples.

Observing the epoch of reionization with LOFAR: progress and challenges

Special Colloquium
Dr. Florent Mertens
ORATED
Kapteyn Astronomical Institute, University of Groningen, The Netherlands

Low-frequency observations of the redshifted 21-cm line promise to open a new window onto the first billion years of the cosmic history, allowing us to directly study the astrophysical processes occurring during the Epoch of Reionization (EoR) and the Cosmic Dawn (CD). This exciting goal is challenged by the difficulty of extracting the feeble 21-cm signal buried under astrophysical foregrounds orders of magnitude brighter and contaminated by numerous instrumental systematics. Several experiments such as LOFAR, MWA, and PAPER are currently underway aiming at statistically detecting the 21-cm brightness temperature fluctuations from the EoR. While no detection is yet in sight, considerable progress has been made recently. In this talk I will review the latest development of the LOFAR-EoR project, focusing on the calibration and foregrounds mitigation challenges. In this regards, I will present a new technique based on Gaussian Process Regression (GPR) able to separate the cosmological signal from the foregrounds contaminants. Finally, I will discuss our latest results, and future perspectives.

Slow and fast transient surveys with the Australian Square Kilometre Array Pathfinder

Special Colloquium
Dr. Shivani Bhandari
ORATED
CSIRO/ATNF, Epping, Australia

The ability to simultaneously observe a large area of the sky with the Australian Square Kilometre Array Pathfinder (ASKAP) has facilitated the wide-field blind searches for slow and fast radio transients. We have conducted an all-Southern sky survey in search for repeating FRBs with ASKAP by re-observing the sky at a different cadence. We have also conducted a pilot survey for slow transients and variable sources. In my talk, I will describe the results from both the slow and fast transient surveys highlighting the role of ASKAP in exploring a different part of the phase space.

ASKAP Fast Radio Bursts

Special Colloquium
Dr. Keith Bannister
ORATED
ATNF/CSIRO, Sydney, Australia

Fast radio bursts are millisecond bursts of radio waves with unknown origin that come from objects at cosmological distances. We have been using the Australian Square Kilometer Array Pathfinder (ASKAP), a 36-dish radio interferometer situated in Western Australia, to find and localise these bursts. I will describe the ASKAP system, and recent results, including 3 sub-arcsecond localisations.

Heavy element synthesis in the Universe

Main Colloquium
Prof. Enrico Ruiz-Ramirez
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 new mobile communications standard 5G from a radio astronomer's perspective

Lunch Colloquium
Dr. Benjamin Winkel
ORATED
Max-Planck-Institut für Radioastronomie

If you follow the news these days, you may get the impression that the upcoming cell-phone technology 5G will make all our lifes much much better. While many people hope that with this new technology you'll finally have internet everywhere and not only in the big cities, 5G is about more than that: low-power consumption, large possible bandwidths, and ultra-low latencies will be important for the internet of things (IoT), where every electronic device is online, but also for self-driving cars, and virtual reality applications. To achieve this goal, the international mobile telecommunications (IMT) industry is asking for a huge new share of the available radio spectrum. Radio astronomy at Gigahertz frequencies is likely to take a massive hit, as we are used to observe at frequencies where we have no allocation. For example, the next WRC is expected to allocate at least the frequencies between 24.25 - 27 GHz to IMT. But even to keep our own bands free of RFI is increasingly challenging. In my talk, I will explain how complex and time-consuming compatibility studies have been, in which we calculate the necessary distances between a 5G cell phone network and a radio observatory.

Fast Radio Bursts and pulsars with the UTMOST telescope

Main Colloquium
Dr. Chris Flynn
ORATED
Swinburne University of Technology, Melbourne, Australia

Fast Radio Bursts (FRBs) are bright, very short (few ms) bursts at radio wavelengths for which the progenitors are unknown. Thousands of FRBs occur daily on the sky to the sensitivity limit of the Parkes Radio Telescope, where they were first found. To date, no FRB has been seen at other than radio wavelengths. They almost certainly lie at cosmological distances, and allow us to probe the Intergalactic Medium in an entirely new way, and potentially measure the baryonic density of the Universe, quite apart from the exciting puzzle of what causes them. I'll report on our FRB detections at the Molonglo Radio Telescope were we have developed a live detection capability commensally with a major pulsar timing program, allowing us to probe FRBs with very high time and frequency resolution. I'll report on results of a major effort at UTMOST (and at the Australian SKA Pathfinder), to localise FRBs to host galaxies, to characterise their source counts at a range of radio frequencies, their temporal and spectral properties, as major steps on the road to understanding their origins.

Unveiling the most elusive components of the universe: the component separation challenge

Special Colloquium
Dr. Mathieu Remazeilles
ORATED
University of Manchester, UK

Outstanding questions in cosmology concern hidden epochs and contents of our universe: dark matter, dark energy, and primordial gravitational waves of quantum origin from cosmic inflation era. Some of these elusive ingredients are expected to have left their footprint on some of the faintest cosmological signals: the yet undetected primordial B-mode polarization of the cosmic microwave background (CMB) radiation should carry the signature of the primordial gravitational waves from inflation; the Sunyaev-Zeldovich (SZ) effects from galaxy clusters and the cosmic infrared background (CIB) radiation from early star-forming galaxies should both trace the distribution of dark matter in the universe. The common aspect of the aforementioned cosmological signals is their faint and/or poorly known signature, obscured by intense astrophysical foreground emissions in nearby universe. We thus face the so-called component separation problem: how to disentangle cosmological signals from astrophysical foregrounds in the millimetre and radio sky observations. Component separation has become a cross-disciplinary research at the intersection of statistics, signal processing, and astronomy. It is recognized as the key challenge for current and future CMB and radio surveys. We will discuss the problem of foregrounds and describe novel component separation approaches that extend beyond usual spectral model fitting to overcome spectral degeneracies (and other degeneracies) between some components of emission. We will show diverse applications ranging from the extraction of kinetic and relativistic SZ effects, the mapping of the CIB, and the detection of the primordial B-modes.

Multi-wavelength variability on blazars and its relation with the pc-scale jet.

Lunch Colloquium
Dr. Víctor M. Patiño-Álvarez
ORATED
MPI für Radioastronomie

In this talk, I present the results from the research done on the sources 3C 279 and 3C 273. We use multi-wavelength light curves spanning over 6 years, from radio to gamma-rays, in order to decipher the stratification of the different emission regions as well as the dominant emission mechanisms. In addition, I present the successful location of a gamma-ray emission zone in the blazar 3C 279, as well as a brief explanation of how misinterpreted statistics can lead to erroneous conclusions on this matter.

Galaxy cluster cosmology from surveys of the hot Universe

Special Colloquium
Dr. Nicolas Clerc
ORATED
Institut de Recherche en Astrophysique et Planétologie, Toulouse

Tracing the formation and evolution of the large-scale structure through its most massive constituents involves consideration of both galaxy cluster astrophysics (how do these objects form and take shape? what are they made of?) and population studies (how are they distributed in space? how similar are they to each other?); a specificity that is famously reflected in the problem of determining a cluster's mass. I will present key aspects of the eROSITA all-sky survey and its forecasted ~100 000 cluster sample, and show that its exploitation will not escape this necessity. In this context, association with large optical and radio surveys stands as a unique way to classify, select, measure objects for cosmology studies. On the other hand, detailed astrophysical studies of clusters enabled by the high-resolution X-ray spectrometer XIFU onboard the future ESA mission Athena will require well-understood samples to pinpoint the physics at play in their hot atmospheres. I will illustrate this reciprocity in perspective of measuring turbulent motions in the gaseous intra-cluster medium.

ICRF3, the new fundamental celestial reference frame of the IAU

Main Colloquium
Dr. Patrick Charlot
ORATED
Laboratoire d'Astrophysique de Bordeaux, France

At its XXXth General Assembly in Vienna last August, the IAU adopted a new fundamental celestial reference frame. This new frame, ICRF3, was built by a Working Group of the IAU mandated for this purpose. It is the third realization of the International Celestial Reference Frame (ICRF) and follows up on the initial realization of the ICRF completed in 1997 and its successor adopted as a replacement in 2009. ICRF3 incorporates nearly 40 years of VLBI data at the standard geodetic and astrometric frequencies (2.3 and 8.4 GHz) together with additional data collected at higher frequencies (24 GHz and 8.4/32 GHz) over the past 15 years. The modeling integrates for the first time the effect of the Galactocentric acceleration of the Solar System which, if not considered, produces significant deformation of the frame due the data span. ICRF3 contains positions for 4536 extragalactic sources, as measured at 8 GHz, 303 of which, uniformly distributed on the sky, are identified as defining sources and as such serve to define the axes of the frame. Positions at 8 GHz are supplemented with positions at 24 GHz for 824 sources and at 32 GHz for 678 sources. In all, 600 sources have three-frequency positions available. The positions were estimated independently at each of the three radio frequencies in order to preserve the underlying astrophysical content behind such estimates. Compared to ICRF2, the median position uncertainty in ICRF3 is reduced by a factor of 3.5, while the noise floor in the individual source coordinates is now at the level of 30 µas. Comparing ICRF3 with the Gaia CRF2 optical frame, which is part of the Gaia Data Release 2, shows no deformations at the level of 30 µas between the two frames.

Microscopic simulations of interstellar and laboratory ice structure and chemistry

Main Colloquium
Prof. Robin Garrod
ORATED
University of Virginia

Laboratory ice experiments play a crucial role in determining the behavior of dust-grain surface chemistry in interstellar and star-forming regions. An important determinant of this behavior is the structure of the ice in which the molecules exist, and thus the mechanisms and means by which the ices are formed (i.e. surface reactions, direct deposition, angle of deposition, surface temperature). Trapping of volatile molecules (e.g. CO) in porous structures within water ice is a particularly well-known phenomenon, and the extra surface area provided by pores may also lead to enhanced surface-chemical effects in cases where the ice constituents are chemically active. In order to properly extrapolate these measurable effects from laboratory conditions and timescales out to those of the interstellar medium requires microscopic chemical kinetic models that can first explain the experimental data. Using the off-lattice Monte Carlo chemical kinetics model MIMICK, we have been working toward a self-consistent set of models that can be used to reproduce each stage of an astrophysical ice experiment, beginning with the simple deposition of water, and the build-up of porous structure. These models can then be directly translated from periodic boundary conditions to a three-dimensional simulation of an individual dust grain. I will present a selection of simulations of both interstellar and laboratory ice formation. I will demonstrate how different mechanisms affect the porous structures of the ices that are formed, and how we expect them to evolve over astrophysical timescales. These simulations provide a critical link between experimental and observational astrochemistry.

Three-mirror anastigmat for cosmic microwave background observations

Special Colloquium
Dr. Stephen Padin
ORATED
University of Chicago, USA

Future CMB experiments will require exquisitely sensitive observations on degree scales to detect inflationary b-modes, and on arcminute scales for delensing. In this talk, I will discuss the possibility of making the observations using a single telescope, with several key features that have not previously been combined in a large telescope design: high throughput to support many detectors; single-piece mirrors to minimize scattering; a comoving ground shield around the entire telescope to reduce pickup; and boresight rotation for measuring polarization errors.

The 10m South Pole Telescope (SPT): Results and Plans

Special Colloquium
Prof. John Carlstrom
ORATED
University of Chicago, USA

This talk will provide an overview of the current and planned 10m South Pole Telescope (SPT) program, including the instrumentation as well as the cosmology and astrophysics results and projections. The results include precision cosmology tests and constraints on cosmological parameters from measurements of the CMB temperature and polarization anisotropies and from measurements of the Sunyaev-Zel'dovich effects, and the discovery of a population of high redshift dusty star forming galaxies and protoclusters of galaxies.

Helioseismology

Main Colloquium
Prof. Laurent Gizon
ORATED
Max-Planck-Institut für Sonnensystemforschung, Goettingen

How does the solar dynamo work? In order to address this challenging question, we need to understand all the components of motion that maintain the magnetic field in the solar convection zone, using helioseismology. Solar acoustic oscillations have been observed nearly continuously at high spatial resolution for over 20 years by dedicated observatories from space and the ground. The science of helioseismology consists of interpreting the frequencies, amplitudes and phases of the oscillations seen at the surface to make 2D and 3D images of the flows in the solar interior. Important results include, for example, maps of internal rotation (as a function of radius and latitude) and flow patterns associated with convection and magnetic activity. In this presentation I will especially report about the very recent discovery of a new component of solar dynamics at large spatial scales: global equatorial Rossby waves.

Fifty-two Years of Observations of the Galactic Center in the Infrared

Special Colloquium
Prof. Eric Becklin
ORATED
SOFIA/USRA and University of California, Los Angeles

In 1964 I started working as a Graduate Student with Gerry Neugebauer and Bob Leighton on the 2.2 micron Sky Survey at Mount Wilson. This led to the first measurements of the infrared radiation from the center of the Milky Way Galaxy in 1966 centered on the radio source Sgr A. I will tell the story of that first discovery and follow up that occurred in the 1970 and 1980's at The Palomar 200 inch telescope, Mount Wilson telescopes, Mauna Kea Hawaii telescopes and especially on the KAO flying 0.9 meter telescope. This included both measurement of stars and dust in the region centered near SgrA* the newly discovered radio point source. The most interesting KAO observation led to the discovery of a ring of dust around Sgr A* (work with Mike Werner and Ian Gatley). In 1995, Andrea Ghez, Mark Morris and I started looking for evidence of a possible massive Black Hole in the Galactic Center. Spectacular observations using the Keck 10 meter telescopes with large format near-infrared arrays and adaptive optics led to the confirmation of the presence of such a black hole and an estimate of its mass (4xE6 M(Sun)). In addition Mark, Andrea and I with the key additions of Leo Meyer, Gunther Witzel and others began multi-wavelength observations of Sgr A*. I will discuss briefly these fabulous results. In 1996, I began working on the Stratospheric Observatory For Infrared Astronomy (SOFIA) and I will finish my talk by discussing SOFIA observations of the ring of dust and gas orbiting the massive black hole in the center of our Galaxy and other recent discoveries.

Are black holes structureless?

Special Colloquium
Prof. Betti Hartmann
ORATED
Universidade de São Paulo, Brazil

Black holes seem to be fascinatingly structureless - in contrast to other compact, but horizonless objects. Recent gravitational wave observations from the collision of two black holes have demonstrated that these events only produced gravitational and no other radiation. These observational results agree with the theoretical prediction that black holes can be described by a very small number of conserved quantities - mass, charge and angular momentum. However, models appearing in theories that try to explain, e.g., the nature of dark energy or the inflationary epoch in the primordial universe as well as recent studies in applications of the gauge/gravity duality contain black hole solutions that often carry so-called "hair", i.e. non-trivial fields on the event horizon. I will give a review on the current status of the so-called "No hair conjecture" and also mention recent studies and applications of black holes that carry additional structure.

Short review on high-mass star formation

Special Colloquium
Dr. Fabien Louvet
ORATED
Facultad de ciencas fisicas y matematicas, Universidad de Chile, Santiago, Chile

Massive star formation is a key astrophysical process. Despite representing only ~1% of the Galactic stellar population, massive stars (M* > 8 Msun) input more energy and momentum into the interstellar medium than the other 99% combined. In other words, massive stars govern the energy budget of galaxies and regulate their evolution across the Universe. However, many unknowns still remain, especially regarding the earliest stages of their formation. In this short presentation, I will present three cornerstones in the process of high-mass star formation: i) how to form the hyper-dense, hyper-massive molecular clouds in which massive stars preferentially form ii) how these molecular clouds form high mass stars (dynamical versus quasi-static evolution) and iii) how to circumvent the radiation pressure issue at small scale.

Characterising the physical properties of the ISM from molecular emission

SFB Colloquium
Dr. Pierre Gratier
CANCELED
Laboratoire d'Astrophysique de Bordeaux, France

New receivers and spectrometers installed at millimeter and submillimeter telescopes now have very large bandwidths spanning tens of gigahertz at very high resolutions (~50-200kHz) yielding spectra comprising of hundred of thousands channels. These observing modes are now standard, which means that spectral surveys are now the observations obtained by default. With these instruments, large, several square degree, maps of the ISM are starting to be observed yielding massive hyperspectral datasets combining the emission of tens of species. The observed line intensities are function of both the ISM chemical composition and physical condition; using these molecular datasets it is possible to extract these ISM properties. In the framework of the ORIONB IRAM 30m large program we have developed statistical methods to study the physical conditions of the ISM solely from the observed molecular emission. I will present in particular: i) the application of a Principal Component Analysis to decompose the maps into regions of low/high density and low/high UV illumination (Gratier et al. 2017), ii) the application of the MeanShift clustering algorithm to segment the molecular cloud into physically and chemically similar regions (Bron et al. 2018) and, iii) preliminary results on the application of supervised machine learning to infer the total column density from molecular emission.

Accretion and Feedback in High-Mass Star Formation

Main Colloquium
Dr. Rolf Kuiper
ORATED
University of Tübingen

In the course of their accretion phase, massive (proto)stars impact their natal environment in a variety of feedback effects such as thermal heating, MHD-driven protostellar jets and outflows, radiation forces, and photoionization / HII regions. Here, I present our most recent simulation results in terms of the relative strength of the feedback components and the size of the reservoir from which the forming stars gain their masses. For the first time, these simulations include all of the feedback effects mentioned above which allows us to shed light on the physical reason for the upper mass limit of present-day stars. Furthermore, we predict the fragmentation of massive circumstellar accretion disks as a viable road to the formation of spectroscopic massive binaries and the recently observed strong accretion bursts in high-mass star forming regions. To advertise our latest code development, I will also overview the most recent results obtained in a variety of other astrophysical research fields from the formation of embedded Super-Earth planets' first atmospheres (Cimerman et al. 2017, MNRAS) to the formation of the progenitors of the first supermassive black holes in the early universe (Hirano et al. 2017, Science).