General Seminar (2024)
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General Seminar takes place every Monday at 11.15 in Piwnice, radioastronomy seminar room.
Remote participation via the BigBlueButton (BBB).
8 January 2024
Cancelled
15 January 2024
“Interstellar medium of spiral galaxies heated by magnetic reconnection?”
dr Marek Weżgowiec (Astronomical Observatory, Jagiellonian University)
Abstract:
In several face-on spiral galaxies a similar spiral structure of the ordered magnetic fields have been observed using sensitive radio polarimetry. These so-called magnetic arms are ‘phase-shifted’ with the spiral arms and their nature is not fully understood. This behaviour of the magnetic fields might be explained by magnetic reconnection that would increase their ordering. Theoretical studies show that magnetic reconnection at the same time can efficiently heat the low-density interstellar medium. To study both effects in more detail we used the XMM-Newton X-ray data and the VLA/Effelsberg radio polarimetric data for several galaxies in which the magnetic arms were found. We compared the properties of the magnetic fields (strengths and energy densities) and of the hot gas (temperatures and energy densities) in selected areas of galactic disks. The analysis revealed signatures of possible increase in thermal energy of the hot gas that can be attributed to the action of magnetic reconnection effects. This seems to be more easily detected in the inter-arm regions than in the spiral arms of galaxies. Our studies also suggest that such ‘reconnection heating’ may be also efficient in galactic halos, where the density of the ISM is lowest.
22 January 2024
“Chemically-homogeneously evolving stars in the dwarf galaxy IZw18?”
dr Dorottya Szécsi (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
Chemically-homogeneously evolving stars have been proposed to account for several exotic phenomena, including gamma-ray bursts, gravitational-wave emissions and certain types of supernovae. Here I show how these stars can account for observations of the metal-poor dwarf galaxy, I Zwicky 18. Applying new PoWR synthetic spectral models to predict the photonionizing flux and the strength of observable stellar lines from a I Zw 18-like population, we compare the results to all available optical and UV data from the literature. We show that the measurements are consistently explained by our models. The source of the stellar emission, such as the UV C-IV (λ1550 Å) line, is a handful of WN and/or WO-type Wolf–Rayet stars (skipping the WC phase completely, which contradicts what was previously assumed), while the high He-II ionizing flux is accounted for by the chemically-homogeneously evolving stars which happen to be extremely hot.
29 January 2024
“Towards a holistic understanding of sub-Neptunes.”
dr Rafael Luque (Department of Astronomy and Astrophysics, University of Chicago)
Abstract:
The nature and origin of sub-Neptune-sized planets is arguably the hottest debate in the field of exoplanets nowadays. While absent in the Solar System, they are the most common planet type in the Galaxy. Multiple models (gas dwarfs, water worlds, Hycean planets) appear to explain current observational evidence from mass-radius measurements and demographic analyses. JWST promises to break those degeneracies, but the first robust results are yet to be published. In the meantime, the discovery and characterization of benchmark targets amenable for these studies is the top priority. In this talk, I will give an overview of the questions surrounding the origin of the “Radius gap”, recent sub-Neptune discoveries such as the 6-planet resonant chain orbiting HD 110067, and the latest efforts in the community to detect molecular species in their atmospheres.
5 February 2024
“Populations of short-period super-Earths, sub-Neptunes, and Neptune-sized planets and prospects for their atmospheric characterisation”
dr Grzegorz Nowak (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
Space-based, high-precision photometric missions to detect transiting planets, such as CoRoT, Kepler, Kepler-K2 and TESS, have revolutionised our understanding of extrasolar planets, particularly for the smallest planets of 1-4 Earth radii. Probably the most important result we owe to the original Kepler mission is a bimodal structure in the radius distribution of the close-in (Pp < 100 d) small planets, with a gap around 1.7 R_Earth that separates the two main classes of small planets: presumably rocky super-Earths with radii around 1.2 R_Earth, and sub-Neptunes with radii around 2.4 R_Earth. Detailed studies of the population of small planets with short periods require precise dynamical mass measurements via radial velocities. These measurements, together with radius, provide information about the bulk densities of the planets. However, measurements of mass, radius, and mean density alone are insufficient to answer all questions about their origin, initial formation location, and internal composition. But since different classes of small planets should have different atmospheres with different observable signatures, their atmospheric studies should help us a lot to answer the above questions. In this talk, I am going to present recent radial velocity follow-up results from TESS planetary systems with small planets and prospects for their atmospheric characterisation. These results include two warm Neptunes transiting HIP 9618, four sub-Neptunes orbiting the K dwarf TOI-1246, TOI-1416 - a system with a super-Earth planet with a period of 1.07 days, and TOI-1136 - a new TESS system with six confirmed transiting sub-Neptunes and Neptunes in resonance, and a seventh single-transiting planet candidate around a young (~700 Myr), active G5 dwarf.
26 February 2024
“Tangle of Chaos in Standing Gravitational Waves”
MSc Syed Naqvi (Astronomical Observatory, Jagiellonian University)
Abstract:
Standing waves, well-studied in mechanical and electromagnetic domains, have been studied within the Einstein-Rosen spacetime, representing cylindrical standing gravitational waves. Our study aimed to analyze the behavior of test particles’ orbits within this spacetime. We observed a sensitivity to initial conditions in the trajectories of these particles. Additionally, we discover the fractal associated with this system. Examining the Poincare map, we identified intricate crossings of stable and unstable manifolds at hyperbolic fixed points. A chaotic heteroclinic network further characterized the complex dynamics of massive test particles. Analogous to phenomena such as mechanical vibrations generating Chladni figures and the intricate shapes of Faraday waves, gravitational standing waves produce complex patterns through the interactions of test particles.
4 March 2024
“Clouds vs Cherenkov telescopes: problems and solutions”
prof. dr hab. Julian Sitarek (Computer Simulations Laboratory, University of Łódź)
Abstract:
Very-high-energy (VHE >~100 GeV) gamma rays are absorbed in Earth’s atmosphere and thus cannot be detected directly on Earth. Their fluxes are also typically too low to efficiently study them with satellite instruments. A VHE gamma ray entering the atmosphere initiates an electromagnetic cascade that induces faint flashes of blueish Cherenkov light. Such flashes can be then detected by Imaging Atmospheric Cherenkov Telescopes registering images of passage of individual gamma rays through the atmosphere. The usage of atmosphere as a part of the detector allows us to achieve a collection area of gamma rays over two orders of magnitude higher than the physical size of the detector. But it also introduces systematic errors connected with the atmosphere’s transparency. In particular, cloud presence during the observations can significantly affect the data. In this seminar I will cover different methods used to correct the influence of the clouds. I will show how lack of such a correction introduces bias in the energy estimation of gamma rays. I will present how the affected images of showers are degraded and thus can be confused with background events, lowering the collection area of the telescope. Finally, I will show a novel method of correcting the influence of the clouds already at the image level, and discuss the possibility of measuring the parameters of a cloud directly with the observations by the Cherenkov telescopes.
11 March 2024
“Maneage: a proof-of-concept for rigorous reproducible research papers”
prof. dr hab. Boudewijn Roukema (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
In astronomy, both galactic and extragalactic, we often want to check what other astronomers have done in the final version of their peer-reviewed, published, article, so that we can compare it directly to our own work or so that we can do followup work. In practice, details that are missing from the paper, such as the lack of input parameters, the lack of software versions, missing information about which specific libraries and compilers were used, and how the data were analysed, can force us to spend a month or longer to do this. The idea of reproducible quantitative research papers is that using the same observational or theoretical data or parameters, and the exact same method as the authors, we should be able to calculate identical results, rather than speculate about what the authors did. Astronomers have introduced an approach to this called “Maneage”, which aims to yield peer-reviewed, published papers whose results are reproducible either immediately or a decade later by scientists with basic astronomical software skills (shell, make, gcc). This seminar will present an overview of Maneage (Akhlaghi+2021, CiSE 23, 82 DOI:10.1109/MCSE.2021.3072860, arXiv:2006.03018).
18 March 2024
“Magnetic flux saturation mechanism at accreting black holes”
dr hab. Krzysztof Nalewajko, prof. CAMK PAN (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences)
Abstract:
Black holes (BH) acquire relativistic magnetospheres by accreting magnetized gas. Once they collect significant magnetic flux across the horizon, aided by the spin they can drive powerful relativistic jets by the Blandford-Znajek mechanism. Large enough BH magnetic flux backreacts on the accretion flow, which has been described in terms of arresting or choking. Magnetic flux eruptions have been identified as the mechanism of BH magnetic flux saturation. These eruptions can potentially dissipate a large fraction of magnetic energy in the BH magnetosphere by means of relativistic magnetic reconnection, accelerating particles and producing flares of non-thermal radiation. We analyze the results of 3D general-relativistic ideal magnetohydrodynamic (GRMHD) numerical simulations of accretion flows onto magnetically saturated Kerr BHs, focusing on the initiation of magnetic flux eruptions.
25 March 2024
“Exploring exoplanets with radial velocity observations”
MSc Hannah Osborne (Mullard Space Science Laboratory, University College London, UK)
Abstract:
The first confirmed exoplanet orbiting a main sequence star was detected by the radial velocity (RV) method, and in the nearly 30 years since then the technique has continued to improve. In this talk I will highlight some of the benefits of using RVs to study exoplanets, as well as some of the struggles ? particularly from an observational perspective. I will also present some recent work using RV observations to characterise a newly discovered small planet which sits inside the small planet radius valley and could have a water-world composition. Finally, I will give an overview of what we can expect with future RV observations and the potential implications for exoplanets more generally.
8 April 2024
“Constrained simulations from peculiar velocities”
dr Simon Pfeifer (Leibniz-Institute for Astrophysics Potsdam, Germany)
Abstract:
Constrained simulations aim to reproduce the real Universe not just in a statistical sense but also by matching the positions and properties of observed structures. I will give a broad overview of the field of constrained simulations, and in particular the methodology of the CLUES collaboration, which uses peculiar velocities of galaxies as constraints. I will show some of the achievements from recent years and discuss the next and ongoing projects.
15 April 2024
“The old Milky Way: investigating the past of our Galaxy”
dr hab. Rodolfo Smiljanic, prof. CAMK PAN (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences)
Abstract:
Our knowledge of how the Milky Way formed and evolved is experiencing an on-going revolution, thanks to the overwhelming amount of data produced by several large stellar surveys; Gaia being the most extraordinary example of this. The study of old metal-poor stars is crucial in this context, as long-lived low-mass stars keep in their atmospheres the chemical composition of the interstellar medium at the time and place of their birth. The combination of chemical abundances with stellar orbits, in large samples of metal-poor stars, is revealing the complicated history of mergers that took place in the early stages of the Milky Way. In this seminar, I will summarise on-going work that is being done in my group, with the aim of better understanding the past of the Milky Way. I will discuss how chemical differences are being used to distinguish accreted stars from those formed in situ, the precise dating of the last major merger suffered by the Milky Way, and what accreted stars can tell about the site of r-process nucleosynthesis. I will finish with some perspective for the future, mentioning new surveys and instruments that will help sustain the revolution in this field.
22 April 2024
“Orbital analysis of multiple systems with jovian planets”
prof. dr hab. Krzysztof Goździewski (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
In the past thirty years, a category of planetary systems that includes large Jupiter-like planets has been identified. The gravitational interactions between the components of these systems have a measurable impact on orbital models that describe the observational time series, particularly through radial velocity, astrometric, and chronometric methods. The aim of this presentation is to introduce systems that contain Jovian planets for which it is particularly important to base the orbital model on physical and mathematical principles. These principles are generally described as the N-body problem. In this context, we will analyse a template planetary system HD160691. Iterative studies of such systems provide information on the orbital architecture, distribution of orbital parameters, and planet masses, which may become increasingly important for extended observational intervals as new data becomes available and modelling methods are refined.
29 April 2024
“Understanding exoplanets through their host stars”
prof. Vincent Van Eylen (Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, UK)
Abstract:
During the past 30 years over 5000 exoplanets have been discovered. I review what is known about these planets and their formation. I show how most of what is known about these planets is inferred indirectly through their host stars, making it crucial to understand stellar properties to learn about exoplanet systems. I discuss the architecture of exoplanet systems, and highlight a fascinating paradigm shift in exoplanet science: the realisation that small planets come in two distinct flavours, i.e., super-Earth and sub-Neptune planets, separated by a radius valley. The valley is key to understanding the formation of small planets, as its location and slope as a function of orbital period are shaped by stellar radiation, disk properties, and planet composition. I show what can be learned through detailed modelling of Kepler and TESS transiting planets, and what has been learned through improving stellar parameters using spectroscopy, Gaia, and asteroseismology. Turning to giant planets, I show how TESS observations have been used to infer the occurrence of Jupiters for different types of stars, and what this implies for planet formation models. Finally, I show how homogeneous studies of stellar properties such as mass, radius, and age, are crucial to better understand the diversity of exoplanets and discuss the important role of the upcoming PLATO mission in this regard.
6 May 2024
“The binary context of blue large-amplitude pulsators”
prof. dr hab. Andrzej Pigulski (Astronomical Institute, Faculty of Physics and Astronomy, University of Wrocław, Poland)
Abstract:
Blue large-amplitude pulsators (BLAPs) form a distinctive group of pulsating stars discovered a few years ago and now have about 70 identified members. These stars exhibit pulsation periods ranging from 15 to 60 minutes, characterised by non-sinusoidal light curves with peak-to-peak amplitudes of up to 0.4 mag in the V band. They pulsate radially. In the Hertzsprung-Russell (H-R) diagram, BLAPs are located between hot massive main-sequence stars and hot subdwarfs. Revealing the evolutionary status of BLAPs is presently a big challenge. To address this problem, several different evolutionary scenarios have been proposed. Crucial to these scenarios is the assumption that these stars are or were the members of binary systems. In my talk, I will summarise the current findings related to the binarity of BLAPs and discuss them in the context of the proposed evolutionary scenarios.
13 May 2024
“Oxygen in meteorites”
prof. dr hab. Szymon Kozłowski (Astronomical Observatory, University of Warsaw, Poland)
Abstract:
Oxygen is the third most common element in the Universe. It can be found virtually anywhere on Earth (air, water, rocks) and in the Solar System. Because oxygen exists in the form of three stable isotopes, their relative abundances in meteorites provide us with information on their formation locations. By studying oxygen isotope ratios you can tell if a meteorite is a piece of rock from Earth, Mars, or an asteroid. I am going to review the role of oxygen in meteoritic studies.
20 May 2024
“Solar modulation of galactic cosmic rays”
dr hab. Agnieszka Gil-Świderska, prof. UwS (Institute of Mathematics, Siedlce University; Space Research Centre, Polish Academy of Sciences)
Abstract:
Cosmic rays are charged particles which constantly arrives at our planet There are ~ 90% of protons, ~ 9% of α particles, as well as small quantity electrons and nuclei of heavier elements. Part of the cosmic rays stream reaching Earth is of extragalactic origin, some come from the center of our Galaxy, while the source of cosmic rays of the lowest energies is Sun. A common way to register galactic cosmic ray (GCR) and its variability are measurements made by a global network of ground neutron monitors (NMs), operating continuously since 1951. They measure secondary cosmic rays: the nucleonic component of the atmospheric cascade initiated by primary cosmic rays. NMs show fluctuations in the original cosmic ray intensity. These variations occur as a result of a solar changeability and reflect the level of solar activity. The basic periodicity observed by neutron monitors is the 11-year cycle, which is a reflection of the Schwebe cycle, characterized by consecutive periods of amplified solar activity of about 11 years. There is a high anti-correlation between the number of sunspots that perfectly illustrate the level of solar activity and the GCR changeability. The next cycle is the 22-year Hale cycle, related to the reversal of the Sun’s magnetic field polarity. There are observed also shorter periodicities: connected to solar rotation, as well as transients appearing in solar behavior. During this seminar there will be discussed various aspects of short-term modulation of GCR, based on the neutron monitors observations, as well as mathematical modeling of GCR transport.
27 May 2024
“Astronomical and Engineering Developments Through Establishing Thai National Radio Astronomy Observatory at NARIT”
dr Koichiro Sugiyama (Thai National Radio Astronomy Observatory at the National Astronomical Research Institute of Thailand (NARIT))
Abstract:
The National Astronomical Research Institute of Thailand (NARIT: Public Organization) initiated a national flagship project in 2017 with the empyreal goal of capacity building through the construction of national radio telescopes for radio astronomy and geodesy. To achieve this, NARIT has established the Thai National Radio Astronomy Observatory (TNRO), in Chiangmai, the northern part of Thailand. At this observatory, two radio telescopes have been constructed: one is a 40-m Thai National Radio Telescope (TNRT) in collaboration with Yebes Observatory, MPIfR, and JBCA, and another one is a 13-m VGOS radio telescope as its co-location in collaboration with SHAO. The 40-m TNRT is the largest telescope for radio astronomy in South-East Asia. Its flexible operation with a wide-coverage of observable frequencies 0.3-115 GHz will allow us to uniquely contribute to the time-domain astronomy as well as carry out unbiased surveys for a wide variety of science research fields, which were published in a white paper (accessible via QR code in the figure). Moreover, within the framework of collaboration with VLBI arrays in the world, these TNRT and VGOS telescopes will drastically improve the imaging quality and performances based on its unique geographical location, for both radio astronomy and geodetic VLBI studies.
In this talk, we will provide an overview of these activities in the TNRO with the 1st CfP of the TNRT L-band as the 1st step for scientifically launching (accessible via QR code in the figure) and demonstrate simulations how these TNRO telescopes improve VLBI imaging quality and performances due to their unique geographical location. In addition, as well as introducing other essential facilities and activities in NARIT briefly, we will present future expandability of the TNRO through constructing other telescopes and installing a VLBI data correlator, resulting in establishment of regional VLBI networks in Thailand and South-East Asia.
3 June 2024
“Interstellar vagabonds in the Solar System”
dr Michał Drahus (Astronomical Observatory, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, Kraków, Poland)
Abstract:
The first-known interstellar minor bodies 1I/’Oumuamua and 2I/Borisov are precious to science because, unlike millions of comets and asteroids that formed in our Solar System, they originate from distant planetary systems. The detection of these objects as they passed through the Solar System has opened a new chapter in planetary exploration, creating an unprecedented opportunity to study samples of other planetary systems from up close with the standard tools and techniques of solar system astronomy. I will discuss what we have learned and what we still don’t know about these first messengers, what they tell us about our own and other planetary systems, and what the future of this area of research looks like.
10 June 2024
“Quick Ultra-Violet Kilonova surveyor”
prof. Norbert Werner (Department of Theoretical Physics and Astrophysics, Masaryk University, Brno, Czech Republic)
Abstract:
After briefly summarising the results of the gamma-ray burst detectors on the GRBAlpha and VZLUSAT-2 CubeSats, I will present the status and summarise the science case of the Quick Ultra-Violet Kilonova surveyor—QUVIK mission. QUVIK is an ultra-violet (UV) space telescope on an approximately 130 kg small satellite with a moderately fast re-pointing capability and a real-time alert communication system, approved for a Czech national space mission. The satellite, which is expected to launch in five years, will provide key follow-up capabilities to increase the discovery potential of gravitational wave observatories and future wide-field multi-wavelength surveys. The primary objective of the mission is the measurement of the UV brightness evolution of kilonovae, resulting from mergers of neutron stars, to distinguish between different explosion scenarios. The mission, which is designed to be complementary to the Ultraviolet Transient Astronomy Satellite—ULTRASAT, will also provide unique follow-up capabilities for other transients both in the near- and far-UV bands. Between the observations of transient sources, the satellite will perform observations of other targets of interest for the scientific community, such as stars, stellar systems, and galactic nuclei.
Special Institute of Astronomy Seminar
18 June 2024 (Tuesday!), at 10:15
“The host galaxies and local environments of fast radio bursts”
dr Shivani Bhandari (ASTRON, Netherlands)
Abstract:
Fast Radio Bursts (FRBs) are millisecond-duration transients of intense, coherent radiation that are signposts of extreme astronomical environments. Despite 15 years of research, no conclusive consensus on the progenitor(s) of FRBs has been reached. While it is clear that some FRBs might be produced by magnetars, the diversity of FRB properties, behaviours, and locations implies that this is not the complete answer. Although there has been significant progress in localising FRBs to their hosts, we are still only scratching the surface in terms of the locations in which we can find FRBs. In this talk, I will give an outline of our current understanding of FRB host galaxies and their local surroundings, with a focus on VLBI observations of FRBs.
Special Institute of Astronomy Seminar
24 June 2024
“Multi-wavelength polarization of blazars”
prof. Markus Boettcher (Centre for Space Research, North-West University, Potchefstroom, South Africa)
Abstract:
Blazars are the most numerous extragalactic sources of high-energy and very-high-energy gamma-rays and are bright and variable throughout the entire electromagnetic spectrum. Their non-thermal continuum emission is dominated by radiation from a highly relativistic jet moving closely aligned to our line of sight. Many open questions concerning the physics of particle acceleration and production of the multi wavelength emission remain. Polarization is a key indicator of the structure of magnetic fields in these sources and the role they play in the acceleration and radiation processes. While traditionally, measurements of polarization were possibly only at radio and optical wavelengths, the recent successful launch of the International X-Ray Polarimetry Explorer (IXPE) has opened a new window of X-ray polarimetry. This talk will introduce the principles of the processes to produce and measure polarized multi-wavelength emission and recent results, in particular from IXPE, as well as co-ordinated multi-wavelength observations involving the High Energy Stereoscopic System (H.E.S.S. – the world’s largest currently operating ground-based gamma-ray observatory) and spectropolarimetry using SALT.
7 October 2024
“Whispering in the dark – X-ray faint black holes around OB stars”
dr Koushik Sen (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
Despite the potential of GAIA DR3 to reveal a large population of black holes (BHs), only a few BHs have been discovered to date in orbit with luminous stars without an X-ray counterpart. It has recently been shown that black holes in orbit with main sequence companions seldom form accretion disks, from where observable X-ray flux is conventionally thought to be produced. Yet, even without accretion disks, dissipative processes in the hot, dilute and magnetized plasma around the BH can lead to radiation. For instance, particles accelerated through magnetic reconnection can produce non-thermal emission through synchrotron. We study the X-ray luminosity from this large unidentified population of black holes using detailed binary evolution models computed with MESA, having initial donor masses from 10-90 Msun and orbital periods from 1-3162 d. A significant fraction (0.1% to 50%) of the gravitational potential energy can be converted into non-thermal radiation for realistic particle acceleration efficiency. A population synthesis analysis predicts at least 28 BH+OB star binaries in the Large Magellanic Cloud (LMC) to produce X-ray luminosity above 10**31 erg/s, observable through focused Chandra observations. We identify a population of observed SB1 systems in the LMC comprising O stars with unseen companions above 1.8 Msun that aligns well with our predictions of the orbital period and luminosity distribution of faint X-ray emitting BH+OB star binaries. The peak in the luminosity distribution of OB companions to these faint X-ray-emitting BHs lies around log(L/LSun) ∼ 4.5-5. Finally, the X-ray luminosity from hot accretion flows around the faint BH can be ∼one order of magnitude above the typical X-ray luminosity expected from embedded shocks in the stellar wind of the OB star companion.
14 October 2024
“Binary progenitor systems for Type Ic supernovae”
mgr Martin Solar (Institute Astronomical Observatory, Adam Mickiewicz University, Poznań)
Abstract:
Core-collapse supernovae (SNe) mark the death of massive stars (> 8 Msun), being one of the most important mechanisms that produce heavy elements and halt the star formation in the interstellar medium, so they have a profound impact on galaxy evolution. Details of these processes depend on SN progenitors, however, it is unclear if Type Ic SNe (without hydrogen and helium lines in spectra) originate from the core-collapse of very massive stars or from less massive in binary systems. In order to constrain the respective progenitor lifetimes and initial masses, we study the molecular gas environments using high-resolution ALMA CO(2-1) observations, being the first statistically significant study of Type II and Ic SNe at scales comparable to giant molecular clouds. We show that Type II and Type Ic SNe are located in environments with similar molecular densities. This implies that their progenitors have comparable lifetimes, and therefore, equivalent initial masses. Our results support a binary model for most Type Ic SN progenitors, arguing that the stripping of outer layers (lack of hydrogen and helium) is due to the interaction with a companion star. This finding can be used to compute the SN metal production, and be implemented in sub-grid processes in order to improve the feedback and chemical mixing in numerical cosmological simulations.
21 October 2024
“Charting the main sequence of star-forming galaxies out to redshifts z~5.7”
dr Maciej Koprowski (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
The increasing amount of multiwavelength data, obtained as part of wide-field and deep surveys, enables a progressively detailed examination of large samples of galaxies. In this talk I will present a new determination of the so-called star-forming main sequence (MS), obtained through stacking ~100k K-band-selected galaxies in the far-infrared Herschel and James Clerk Maxwell Telescope imaging. I will explain how the dust emission curve was fitted to the stacked FIR photometry, in order to determine the IR luminosities and hence the star formation rates out to z~5.7. How the functional form of the MS was found, and describe why it flattens at high stellar masses and its normalization increases exponentially with redshift. I will compare my findings with the literature and explain the slight differences found. In addition, I will explain how other star-forming galaxies’ relationships were determined, like the dependence of the peak dust temperature (Td) on redshift and the redshift evolution of the specific star formation rate. Finally, I will show how can we inspect the derived shape of the star-forming MS by simulating the time evolution of the observed galaxy stellar mass function.
28 October 2024
“From unveiling Giant Radio Galaxies to harnessing them as astrophysical probes”
dr Pratik Dabhade (Astrophysics Division, National Centre for Nuclear Research, Warsaw)
Abstract:
Giant Radio Galaxies (GRGs) are home to active supermassive black holes that produce powerful bipolar radio jets, creating structures that extend over megaparsec scales. These are the largest structures in the Universe, growing up to ~7 Mpc and even surpassing the size of massive galaxy clusters. Though discovered 50 years ago, significant progress in understanding GRGs has been made only in the past eight years, largely due to the efforts of the SAGAN project (‘Search & Analysis of GRGs with Associated Nuclei’).
Research continues to explore whether the immense size of GRGs is driven by their efficient AGN or the sparser environments in which they reside. The SAGAN project, initiated in 2016, has produced eight research papers, including a review, discovering the largest samples of GRGs and refining our understanding of their key properties. The project has rejuvenated global interest in these giant radio sources.
This seminar will review how our understanding of GRGs has evolved with deep radio surveys like LoTSS, which have uncovered the largest and faintest GRGs. We will discuss optical-infrared data from SDSS and WISE, revealing AGN accretion properties, and millimetre-wave data from IRAM, offering insights into AGN fuelling. We will also showcase GMRT radio images revealing previously unseen low-surface-brightness structures in GRGs, enabling more precise age and magnetic field estimates. Lastly, we will demonstrate how GRGs can be used as cosmic probes of large-scale environments and magnetic fields, with key implications for understanding magnetogenesis.
4 November 2024
“The ongoing story of the VIPERS nuggets”
mgr Krzysztof Lisiecki (National Centre for Nuclear Research, Warsaw)
Abstract:
High-redshift galaxies are significantly more compact than their local counterparts. Dense and massive galaxies, called nuggets, are formed as starburst objects. During the first phase of their formation, nuggets do not grow in size, as their growth is due to in situ star formation. Later on, the main growing mechanism changes from in situ star formation to mergers and interactions with other galaxies which result in growth, contrary to the previous phase, also in size. However, since mergers are stochastic events, some of the nuggets can escape their fate and survive for billions of years without interactions with other galaxies. Such isolated objects and their stellar populations are perfect samples for modeling star formation histories and quenching mechanisms, but also entangling the galaxy evolution models.
Due to the unique nature of the nuggets, we have built the first spectroscopically confirmed catalog at redshift 0.7 of these galaxies from the VIMOS Public Extragalactic Redshift Survey (VIPERS). We analyzed the importance of the nugget’s environment and what is the main quenching driver for nuggets in the early phase. The important question is how we can connect nuggets to post-starburst galaxies. I will present our findings during the talk. Moreover, I will also present one case study of a nugget which explores new territories of the global description.