General Seminar (2021)
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General Seminar takes place every Monday at 11.15 in Piwnice, radioastronomy seminar room.
Since April 27th, 2020 the seminar is in a remote mode.
Remote participation via the BBB or WEBEX virtual seminar room.
4 January 2021
“Observations of maser emission performed with RT4”
MSc Michał Durjasz (Institute of Astronomy, Nicolaus Copernicus University)
Toruń 32-m radio telescope RT4 participates in numerous VLBI sessions every year – but what it does when the sessions are over? It mostly observes maser emission that origins in vicinity of massive protostars. Surveys of the OH masers at 6 GHz and methanol masers at 12 GHz resulted in finding new sources – detection of multiple lines that originate in the same place allows us to constrain physical properties around young massive stars. Also, Zeeman pairs of the OH masers are useful in research of magnetic fields. We also managed to detect 6.7 GHz methanol maser flares due to regular monitoring.
11 January 2021
“Spectroscopy of the helium-rich binary ES Ceti reveals accretion via a disc and evidence for eclipses”
Dr Karolina Bąkowska (Institute of Astronomy, Nicolaus Copernicus University)
Amongst the hydrogen-deficient accreting binaries known as the “AM CVn stars” are three systems with the shortest known orbital periods: HM Cnc (321 sec), V407 Vul (569 sec) and ES Cet (620 sec). These compact binaries are predicted to be strong sources of persistent gravitational wave radiation. HM Cnc and V407 Vul are undergoing direct impact accretion in which matter transferred from their donor hits the accreting white dwarfs directly. ES Cet is the longest period of the three and is amongst the most luminous AM CVn stars, but it is not known whether it accretes via a disk or direct impact. ES Cet displays strong HeII 4686 line emission, which is sometimes a sign of magnetically-controlled accretion. Peculiarly, although around one-third of hydrogen accreting white dwarfs show evidence for magnetism, none have been found amongst helium accretors.
We present the results of Magellan and VLT spectroscopic and spectropolarimetric observing campaigns dedicated to ES Cet with the aim of understanding its accretion structure.
We find strong variability in our spectra in the 620 sec period. The lines show evidence for double-peaked emission, characteristic for an accretion disc, with an additional component associated with the outermost disc, rather than a direct impact, that is broadly consistent with “S”-wave emission from the gas stream/disc impact region. This confirms beyond any doubt that 620 sec is the orbital period of ES Cet. We find no significant circular polarisation (below 0.1 %). The trailed spectra show that ES Cet’s outer disc is eclipsed by the mass donor, revealing at the same time that the photometric minimum coincides with the hitherto unrecognised eclipse.
ES Cet shows spectroscopic behaviour consistent with accretion via a disc and is the shortest orbital period eclipsing AM CVn star known.
18 January 2021
“Variability in SMEI data”
MSc Przemysław Mikołajczyk (Astronomical Institute, University of Wrocław)
The Solar Mass-Ejection Imager (SMEI) was an experiment designed to detect and measure transient plasma features in the heliosphere, including colornal mass ejections. As it was observing the whole sky with its three cameras with total field-of-view of 180 deg x 3 deg, images of the whole sky have been taken roughly every one orbit (~100 minutes) for over 8 years. In order to remove bright objects (stars, planets, clusters, SolarSystem minor bodies etc.) PSF photometry has been performed. Time-series photometry for ~5600 objects is a side effect of SMEI performing its main objective. In my presentation, I will show what the SMEI data looks like and highlight existing differences between the two data releases. I will discuss the data quality and show methods to improve quality of PSF photometry. Finally, I will show some examples of SMEI data analysis regarding known variable sources as well as the results of a variability survey among O and B stars, which constitute a major part of my PhD thesis.
22 February 2021
“Statistical analysis of blazar variability”
Dr Arti Goyal (Astronomical Observatory, Jagiellonian University, Kraków)
The power-law form of blazar variability power spectral densities (PSDs) with slopes ranging from 1–3 indicate that the variability is generated by underlying colored noise type stochastic processes. Here, we present the results of our PSD analysis using both Fourier domain and time domain approaches on multiwavelength datasets (GHz band radio–very high energy gamma–ray energies) and covering timescales ranging from a few decades to minutes. Our main results are the following: (1) nature of the variability process at synchrotron frequencies is different from those at Inverse Compton frequencies (slopes 2 and 1) of the emission spectrum; this could imply, that gamma-ray variability, unlike the synchrotron (radio-to-optical) one, is generated by the superposition of two stochastic processes with different relaxation timescales, (2) the main driver behind the optical variability is same on decades, years, months, days, and hours timescales (slope=2), which argues against the scenario where different drivers behind the long-term and intra-night flux changes are considered. Our results do not easily fit into a simple model, in which a single compact emission zone dominates the radiative output of blazar across all the timescales probed. Instead, we argue that the frequency-dependent shape of the variability power spectra points out a more complex picture, with highly inhomogeneous outflow producing non-thermal emission over an extended, stratified volume.
1 March 2021
“Planetary migration, periodic orbits and mean motion resonances”
Dr hab. Cezary Migaszewski (Institute of Astronomy, Nicolaus Copernicus University)
This talk is devoted to the relationship between planetary migration and mean motion resonances. The stabilising role of the latter is discussed in the context of data analysis and characterisation of multi-planet systems, especially those that are poorly constrained by observations. Particular emphasis is placed on periodic orbits as centres of resonance. Knowledge of such configurations can be used to properly interpret observations, which in turn can help to better relate observational characterisation results of known planetary systems to their migration-induced formation models.
8 March 2021
“Constraints on the efficiency of convective transport from asteroseismology of AF-type stars”
Prof. dr hab. Jadwiga Daszyńska-Daszkiewicz (Astronomical Institute, University of Wrocław)
Depending on physical conditions inside a star, the energy produced in the centre can be transported to the surface by radiation, convection or conduction. The treatment of stellar convection in the outer layers is one of the most fundamental problems in stellar physics. The motion of a convective element is extremely difficult to describe and, usually, it is done in stellar evolution calculations in the framework of the so-called mixing-length theory (MLT). The convective efficiency within MLT is measured by the parameter $\alpha_MLT$, the value of which cannot be derived from the first principles.
In this talk, I will present what information about convection in stellar envelopes can be obtained from asteroseismic studies of the main sequence pulsators of AF spectral type. I will discuss the results for the two stars: SX Phoenicis and $\delta$ Scuti. These stars are the prototypes of a class of pulsating stars of Population II and Population I, respectively.
15 March 2021
“Sky surveys at CAPS: DES, DELVE, and LSST”
Dr Monika Adamów (National Center for Supercomputing Applications (NCSA) University of Illinois at Urbana-Champaign)
The Center for Astrophysical Surveys (CAPS) at the University of Illinois at Urbana-Champaign is involved in several sky surveys. In my presentation, I would like to advertise three of them: Dark Energy Survey and DELVE, both with very recent public data releases, and Legacy Survey of Space and Time (LSST) – a project conducted by Vera C. Rubin Observatory. This project is currently in the construction/commissioning phase, with the regular science operations planned for the beginning of 2023.
22 March 2021
“Eppur si muove. On the Origin of Long Secondary Periods in Red Giant Stars”
Prof. dr hab. Igor Soszyński (Astronomical Observatory, University of Warsaw)
Long secondary periods (LSPs), observed in a third of pulsating red giant and supergiant stars, are the only unexplained type of large-amplitude stellar variability known at this time. Numerous authors have explored various scenarios for the origin of LSPs, but were unable to give a final solution to this problem. I will present known properties of LSP variables and show new results proving that the physical mechanism responsible for LSPs is binarity. Namely, the LSP light changes are due to the presence of a dusty cloud orbiting the red giant together with the brown-dwarf companion and obscuring the star once per orbit. In this scenario, the low-mass companion is a former Jupiter-like planet that accreted a significant amount of mass from the envelope of its host star and grown into a brown dwarf.
29 March 2021
“Doing peripheral science? Johannes Hevelius, Maria Cunitia and Elias von Löwen and the development of astronomy in the 1st half of the 17th century”
Prof. dr hab. Jarosław Włodarczyk (Institute for the History of Science, Polish Academy of Sciences, Warsaw)
The correspondence of Johannes Hevelius (1611–1687) comprises a set of 22 letters written in the years 1648–1654 and exchanged with Maria Cunitia (1610–1664) and her husband, Elias von Löwen (Crätschmair, c. 1602–1661), a couple based in Silesia. Maria Cunitia is acknowledged for her Urania Propitia (1650), an innovative adaptation of the mathematical astronomy of Johannes Kepler’s Rudolphine Tables (1627). In turn von Löwen authored astronomical calendars and ephemerids.The letters can be seen as an extraordinary example of the exchange of thoughts involving, on the one hand, a representatives of the mainstream European astronomy of the 17th century (Hevelius) based in an acknowledged scientific center (Gdańsk) and, on the other, astronomers working in the periphery of then scientific Europe. The correspondence features several significant astronomical themes, which cast new light on the activities of astronomers in the first half of the 17th century, and even on the chronology of discoveries. These include telescopic observations of the positions of the planets made to verify the accuracy of astronomical tables, studies of the optical libration of the Moon in the period preceding Galileo Galilei and Hevelius, discussion of the usefulness of various observational tools such as the telescope, the ways of purchasing telescopes in the first half of the 17th century and their dissemination outside major scientific centers. The correspondence proves unique because it describes the activities of astronomers who work independently and far away from the major academic centers. Furthermore, the fact that it is a woman who seems to be the major vehicle of the 17th century scientific inquiries, makes the letters a particularly interesting source for researches of social history and history of science, including those with feminist agenda.
12 April 2021
“Gamma-ray emission from collisions of stars with jets in active galaxies”
Prof. dr hab. Włodzimierz Bednarek (University of Lodz)
Vicinity of super-massive black holes (SMBHs) in many galaxies are well established sites of high energy processes in which high energy gamma-rays are produced. This radiation is commonly believed to originate in relativistic collimated outflows which are powered by the accretion process onto SMBHs. On the other hand, SMBHs are surrounded by huge quasi-spherical systems of young stars on parsec distance scale, stars from the bulge on sub-kpc distance scale and also many globular clusters on kpc distance scale. Those stars (and stellar systems) can enter the jet region from time to time disturbing the jet flow and creating soft radiation field for energetic particles. The aim of the talk is to review a few scenarios in terms of which basic proprieties of gamma-ray emission can be understood. In particular, we discuss the gamma-ray production in the interaction of relativistic electrons: (I) accelerated on the shock around massive star and (II) the shock around globular cluster; (III) electrons accelerated within the relativistic blob in the jet; and (IV) gamma-rays, produced in the inner jet but, interacting with the radiation of a star crossing close to the direction towards the distant observer. Possible applications of those models to the recent gamma-ray observations by the satellite and Cerenkov telescopes will be also discussed.
19 April 2021
“Random flows and rotation in galactic coronae”
Prof. Anvar Shukurov (School of Mathematics, Statistics and Physics, Newcastle University)
Galactic coronae are extended gas envelopes around the discs of spiral galaxies filled with a hot, rarefied gas produced by supernovae in the disc. They contain cosmic rays and magnetic fields and provide a reservoir for the magnetic helicity transported from the disc by the fountain flow. The nature and parameters of the turbulence and rotation in the coronae are poorly known and the existing rotation models struggle to explain the limited observations available. We discuss the sources of random motions in the coronae and argue that the gas is so viscous that developed turbulence cannot be maintained. We suggest that the observations are compatible with the diffusive spread of vorticity from the disc.
26 April 2021
“LOFAR Surveys: a new window on the Universe”
Prof. Huub Rottgering (Leiden Observatory)
The Low-Frequency Array (LOFAR) is a pan-European radio telescope whose massive data taking and processing capabilities make it an unprecedented powerful instrument for carrying out the deepest and widest radio surveys at low radio frequencies. Over the last years we have addressed important issues related to the analysis and calibration of the radio data so that we can now make thermal noise limited maps at low frequencies. The resulting wide and deep maps enable studies of a wide range of scientific topics ranging from (i) shocks in merging clusters, (ii) radio feedback processes, (iii) star formation in distant galaxies and (iv) the most distant radio galaxies, close to the epoch of reionisation.
In this talk I will first discuss our solutions to the main technical challenges. Secondly, scientific highlights will be given related to these 4 topics.
The seminar is organised as part of the academic partnership between NCU in Torun and Leiden University within the framework of the InterAPS project.
10 May 2021
“Investigating the most promising Yarkovsky candidates using Gaia DR2 astrometry”
MSc Karolina Dziadura (Institute Astronomical Observatory, Adam Mickiewicz University, Poznań)
The orbital motion of small bodies is affected by the Yarkovsky effect. First-time the effect was proposed by Yarkovsky in 1901 and then popularized by Öpik in the 1950s. However, the first direct detection was only made in 2003 thanks to radar observations. Nowadays there are over hundred detections for NEAs and only a few for Main-Belt objects. The main goal of this study is to improve an asteroid orbit using GAIA DR2 astrometry. It was claimed that the Gaia mission will improve asteroids orbits and to find new Yarkovsky detections thanks to the high precision and accuracy of its astrometry. I converted all of the available data to ADES format and then used it to orbit determination. I used OrbFit software which is a Fortran program for orbit propagation, ephemerides computation, orbit determination, close approach analysis, and impact monitoring. I will show results for 42 asteroids, where for 21 of them I obtained an A2 parameter with signal to noise ratio greater than 3.
17 May 2021
“Monitoring of satellites and space debris and investigating their impact on astronomical observations”
Dr Krzysztof Kamiński (Institute Astronomical Observatory, Adam Mickiewicz University, Poznań)
The growing number of Earth orbiting artificial satellites and space debris raises important questions about human presence in space. Astronomical Observatory of Adam Mickiewicz University is joining the efforts in creating a European network of optical, laser and radar sensors to monitor the orbital evolution of space resident objects and help predict their collisions, atmospheric re-entries etc. This is a part of a wide array of activities orchestrated by the European Space Agency and the European Space Surveillance and Tracking Consortium in order to guarantee long term sustainability of utilization of Earth satellites. Additionally we are monitoring the situation from the point of view of astronomical observations which are threatened to some degree by large satellite constellations. In order to help mitigate the interference between astronomical research and space infrastructure development we are working on an on-line tool for predicting potential satellite signatures in recorded images.
24 May 2021
“Tidal evolution of galaxies in clusters”
Prof. Ewa Luiza Łokas (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw)
Galaxies are subject to strong tidal evolution in the environment of clusters. I will discuss this process using the example of the most massive cluster of the IllustrisTNG-100 simulation that traces the formation and evolution of galaxies in the cosmological context. For the purpose of this work, I selected 112 galaxies in the cluster, with the largest stellar masses at present, and followed their properties over time. Using their orbital history, the sample is divided into unevolved (infalling), weakly evolved (with one pericenter passage), and strongly evolved (with multiple pericenters). The samples are clearly separated by the value of the integrated tidal force from the cluster the galaxies experienced during their entire evolution and their properties depend strongly on this quantity. As a result of tidal stripping, the galaxies lose mass and become significantly less dark matter dominated. The cluster environment is also very efficient in stripping the galaxies of their gas and quenching the star formation. The strongly evolved galaxies lose their gas earlier and faster, and they become redder and more metal rich, so that at redshift z=0.5 the population of galaxies in the cluster becomes predominantly red. As a result of tidal stirring, the morphology of the galaxies evolves from oblate to prolate and their rotation is diminished, thus the morphology-density relation is reproduced in the simulated cluster. The strongly evolved sample contains at least six convincing examples of tidally induced bars and six more galaxies that had their bars enhanced by their interaction with the cluster.
31 May 2021
“Changing paradigms in planet formation”
Dr Joanna Drążkowska (LMU Munich, University Observatory)
Our understanding of planet formation is being transformed thanks to the exoplanet detections and observations of circumstellar disks but also the increasing precision of measurements of the Solar System meteorites. This talk will present the emerging planet formation theory as a multifaceted process that starts with dust growth to pebbles. I will introduce our recent results suggesting that the Solar System architecture as we know it today is intimately connected to the earliest phases of the solar disk evolution.
7 June 2021
“PL-612 LOFAR Baldy station. Current activities and further development”
Dr hab. Leszek Błaszkiewicz (Space Radio-Diagnostics Research Centre, University of Warmia and Mazury in Olsztyn)
The LOFAR radio telescope is an interferometric network initiated in the Netherlands, consisting of stations that are digitally controlled phase telescopes. Currently, 38 stations located in the Netherlands and 14 in other European countries participate in the network, including three in Poland. frequency range (30 – 80 MHz and 110 – 240 MHz) makes the telescope extremely useful in many types of astronomical research. During the lecture, technical aspects of the LOFAR instrument operation will be presented, with an emphasis on the operation of a single station, as well as the observational results obtained both during the observations of the entire system and its separate parts (core, single stations, ILT mode). The upcoming plans for enlargement of the system to the state known as LOFAR 2.0 will also be presented.
4 October 2021
“Classification of Gaia microlensing events and hunt for black holes”
Dr Paweł Zieliński (Astronomical Observatory, University of Warsaw)
Gaia mission scans the entire sky in order to deliver the proper motions and distances for a billion stars. It is capable of detecting the photometric variability of stars like, e.g., microlensing events which are of particular interest in the context of searching for compact objects in our Galaxy. Gaia photometric and astrometric time-series can reveal lensing black holes of stellar masses. But due to Gaia cadence, it is crucial to conduct additionally photometric monitoring of as many microlensing events as possible from the ground. Therefore, a network of small and medium-sized telescopes was developed under the OPTICON grant financed by the EU Horizon2020. Data delivered by the network is being automatically processed and calibrated to science-ready data by using our new tool – Black Hole TOM (https://bh-tom.astrolabs.pl/). Moreover, also the spectroscopic follow-up observations by using world-class telescopes for selected Gaia transients were performed in order to early distinguish genuine microlensing events from other types of outbursts and variables reported by the Gaia Science Alerts system. The spectra helped us classify and select a sample of microlensing events for which an intensive photometric follow-up can be conducted. Thanks to them, we are also able to determine physical parameters of the source star, extinction and distance that is essential in constraining the microlensing model.
During my talk, I am going to present the status of our searches for black holes with recent examples of interesting events, the results of spectroscopic classification of candidates for microlensing events, as well as the capabilities and applications of BHTOM. Such small-scale operations provide good training ahead of the forthcoming influx of Galactic Plane transients from the LSST/VRO.
11 October 2021
“Astrophysics with LIGO/Virgo Gravitational-wave Detections”
Prof. dr hab. Krzysztof Belczyński (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw)
LIGO/Virgo Collaboration has published 50 detections from the first three observational campaigns (O1/O2/O3). The most interesting detections are putting a new perspective on black hole and neutron star formation. I will discuss the landscape of 1/O2/O3 detections and their implications for stellar evolutionary modeling. Broadly speaking, the basic observational properties of detected double black hole mergers are consistent with predictions of the classical isolated binary evolution of massive stars. However, these detections severely constrain stellar physics that is unaccessible by electromagnetic observations.
On the other hand, the first results from the O3 campaign seem to challenge classical binary evolution with black holes found in the lower and upper mass gaps. These are regions in which black holes are not expected to form from stars but rather form via dynamic interactions of stars in dense clusters. I will discuss these curious events in the context of their most likely formation sites.
18 October 2021
“The retrograde world: Where did retrograde asteroids come from?”
Dr Paweł Kankiewicz (Jan Kochanowski University of Kielce)
The asteroids with orbital inclinations greater than 90 degrees are generally known as retrograde asteroids. The first object of this kind was discovered in 1999, and after discoveries in 2007 and 2009, such two objects were classified as near-Earth objects (NEOs). There are various hypotheses related to the physical characteristics and formation of these types of objects. The physical and orbital similarity to comets suggests an origin from their hypothetical reservoir: The Oort Cloud. More recent hypotheses, in turn, do not exclude an interplanetary origin. The presented research and its results are the results of a project that comprehensively investigated the dynamics of bodies in retrograde orbits and verified scenarios of their orbital evolution. Methods were worked out to study their long-term evolution and to determine how long they live and remain in stable orbits in our planetary system. In statistical terms, it was also verified how plausible the scenario of inversion of such orbits is due to perturbations. A possible influence of non-gravitational effects on the results was also investigated.
25 October 2021
“Implications of AGN feedback on high redshift galaxies”
Dr Flora Stanley (Institut d’Astrophysique de Paris)
One of the main open questions of galaxy evolution is how active galactic nuclei (AGN) can affect the ongoing star-formation and interstellar medium (ISM) properties of galaxies. To reproduce the properties of galaxies in the local universe, cosmological and semi-analytical models of galaxy formation and evolution find it necessary to use AGN feedback as a regulator of star formation, in the form of heating and outflows of the surrounding gas. To find observational evidence that AGNs do have a significant role in regulating galaxy growth, we need to study the star formation and ISM properties of active galaxies. In this seminar, I will present the main results from my research on the SFR and ISM properties of AGN across cosmic time.
8 November 2021
“A new insight into the magnetism of degenerate stars from the analysis of a volume-limited sample of white dwarfs”
Dr Stefano Bagnulo (Armagh Observatory and Planetarium, UK)
Many stars evolve into magnetic white dwarfs, but we do not know when the magnetic field appears at their surface, if and how it evolves during the cooling phase, and, above all, what are the mechanisms that generate the field, and why they act on some but not all degenerate stars. Observations may help to find an answer to these questions, but their interpretation is dramatically affected by biases due to target selection and a non-homogeneous field detection threshold. To minimise these biases we have carried out a volume-limited spectropolarimetric survey, and observed more than two-third of the about 150 white dwarfs that lie within 20 pc from the Sun. After combining our new data with previous literature data, we have checked for magnetic field almost the entire population of white dwarfs of the local 20pc volume, with a sensitivity that ranges from better than 1kG for most of the stars of spectral type DA, to about 1 MG for the featureless white dwarfs of spectral type DC. In this talk, I will present the results of our survey, and discuss the implications of our findings in relation to some of the proposals that have been put forward to explain the origin and evolution of magnetic fields in degenerate stars.
15 November 2021
“Cosmic Ray driven galactic winds and their angular momentum dependence”
Dr Nicolas Peschken (Institute of Astronomy, Nicolaus Copernicus University, Toruń)
Cosmic rays, as produced in supernova remnants, have been shown to have a significant impact on galaxy evolution through their dynamical coupling with gas. They travel through advection and diffusion in the ISM, being accelerated by the magnetic field, and can easily escape galactic discs. This in turn translates into large outflows of gas, launching powerful galactic winds affecting the star formation, angular momentum and morphology of galaxies.
In this seminar, I will present my work on the study of such winds using MHD + N-body simulations of spiral galaxies including cosmic rays. Besides understanding the formation and evolution of cosmic ray driven winds, I am particularly interested in the influence of angular momentum on them, and therefore investigate and compare cosmic ray driven outflows for different angular momentum discs. Different amounts of angular momentum lead to different star formation rates, winds strengths, and disc morphologies. I will also show the winds angular momentum structure, as they are feeding from different regions of the disc, removing gas permanently from some areas while supplying others via galactic fountain mechanisms.
22 November 2021
“A three-dimensional map of the Milky Way using classical Cepheid variable stars”
Dr Dorota Skowron (Astronomical Observatory, University of Warsaw)
The Milky Way is a spiral galaxy. This is inferred from various methods, such as radio observations of Galactic gas, star counts, and our extrapolation of structures seen in other galaxies. However, these methods are indirect and rely on many assumptions. Precise mapping of the Milky Way is also difficult because we may only observe it from the inside through clouds of gas and dust. As a result, the exact picture of our Galaxy is still under debate.
However, distances can be accurately measured to Classical Cepheids, which are young pulsating variable stars. I will present a new a comprehensive picture of our Galaxy in three dimensions based on the positions in the sky and precisely measured distances of thousands of these objects.
29 November 2021
“Multi-frequency and multi-epoch study of new transient radio AGNs”
MSc Aleksandra Wołowska (Institute of Astronomy, Nicolaus Copernicus University)
During their lifetime the radio sources go through different phases of development. They start as young and compact Gigahertz-Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources, then expand and become large-scale FRI and FRII objects. The estimated age of an adult radio source is 10^8 years. However, the excess of compact sources in comparison to fully developed radio-galaxies indicates that a part of young radio sources never evolves into extended structures. Among several explanations for this early cessation of radioactivity, there are indications that some sources may be transient objects on timescales of 10^4 – 10^5 years, representing the new population of active galaxies that need to be explored. We would like to present a comprehensive multi-epoch and
multi-wavelength study of twelve radio sources, discovered recently by Caltech-NRAO Stripe 82 Survey (CNSS). This is the first unbiased sample of AGNs, undetected in a previous radio survey, that transitioned to radio-loud state either as a result of the increase in radio power or its ignition. These sources represent a new group of AGNs that have not been thoroughly researched so far and may exhibit behaviour typical of many objects of this class.
6 December 2021
“X-ray binary populations and stellar populations in nearby galaxies”
Prof. Andreas Zezas (Institute of Astrophysics, Foundation for Research and Technology – Hellas and University of Crete)
X-ray binaries are one of the few probes to study the populations of compact objects and the formation of compact-object mergers (e.g. gravitational-wave sources, and/or short GRBs). I will discuss results from Chandra-based studies of the formation efficiency of X-ray binaries in nearby galaxies, and a systematic study of the compact object populations in nearby galaxies observed with NuSTAR which allow us to explore X-ray binary demographics in different galactic environments. We find that High-mass X-ray binaries show enhanced formation rates at ages of ~30-60Myr, with another possible peak around 10Myr, in good agreement with expectations from X-ray binary population synthesis models. Our analysis of the compact-object populations indicates that more actively star-forming galaxies host a larger fraction of black-hole systems. Furthermore, we see a clear preference for accreting pulsars to be associated with star-forming regions, in accordance with similar studies in our Galaxy. We also find that the scaling relations between X-ray luminosity, star-formation rate and stellar mass hold to even sub-galactic scales. Finally, I will discuss recent results from the first eROSITA data which provide a blind unbiased sample of galaxies.
13 December 2021
“X-ray binary populations and stellar populations in nearby galaxies”
Dr Quentin Vigneron (Institute of Astronomy, Nicolaus Copernicus University)
Constructing an extension of Newton’s theory which is defined on a non-Euclidean topology, called a non-Euclidean Newtonian theory, would be a powerful tool to study the influence of global topology on structure formation, especially studying the influence of other topologies than the 3-torus currently used in Newtonian cosmological simulations. That theory would be simpler to use than general relativity, but would still be physical on cosmological scales as is the case with Newton’s theory. We will see that a natural way of defining such a non-Euclidean Newtonian theory is to use the concept of Galilean manifolds along with a minimal modification of the Newton-Cartan equations. The resulting theory has a gravitational system of equations that is algebraically equivalent to cosmological Newton’s equations, but with the presence of a non-zero spatial curvature in the spatial connection present in these equations. While the theory predicts no additional effects (with respect to ΛCDM) of the topology on the expansion of our Universe, it allows for the study of the influence of topology on structure formation through the use of N-Body calculation. For this purpose, I will provide the mass point gravitational potential in some spherical topologies.
20 December 2021
“X-ray binary populations and stellar populations in nearby galaxies”
Dr Robert Beswick (University of Manchester)
Radio emission provides a uniquely powerful and unobscured probe of the two key physical processes underway in, and powering, galaxies and their evolution: Accretion onto their central SMBH, and star-formation processes. To explore these processes, and their role in galaxy evolution, we require very high resolution (sub-arcsecond or better), sensitive imaging at radio wavelengths across large samples of galaxies in both the local and distant universe. In this seminar, I will describe the motivation and latest results from two large ‘sister’ e-MERLIN surveys (the 800-hr Legacy e-MERLIN Multi-band Imaging of Nearby Galaxies (LeMMINGs) and 1000-hr e-MERlin Galaxy Evolution (e-MERGE) surveys) which are using the e-MERLIN (the UK’s National Radio Astronomy facility, and a SKA pathfinder instrument) and NRAO’s VLA. These two projects are currently producing some of the deepest (uJy), sub-arcsecond and milliarcsecond resolution radio imaging of ‘normal’ local galaxies (LeMMINGs – surveying 280 nearby galaxies), and ‘extreme’ distant (up to z~5) galaxies (e-MERGE – 1000hr deep survey of the GOODS-N region). In each of these surveys, we can spatially resolve, at radio wavelengths, the activity powering these galaxies. Combining this with extremely rich multi-wavelength ancillary data these surveys are separating star-formation and accretion at high redshift (allowing analysis of the co-evolution of these processes), and in local galaxies are characterising the role of low-luminosity AGN, providing a key bridge between our understanding between extragalactic AGN sources and accreting galactic black holes.