Black hole-neutron star (BHNS) mergers have recently been detected through their gravitational-wave (GW) emission. Such mergers could also produce electromagnetic emission as a short gamma-ray burst (sGRB), and/or an sGRB afterglow upon interaction with the circummerger medium. In this talk, we present new simulations on the expected detection rates with the Square Kilometre Array Phase 1...
The concurrent detection of GW 170817 and GRB 170817A secured the connection between binary neutron star (BNS) mergers and at least some short-duration gamma-ray bursts (sGRBs), allowing us to link several aspects of the two phenomena. Among the links opened by this connection, one is between the host galaxies of sGRBs and the environment of BNS mergers. From the study of sGRB hosts we can...
The common practice of model validation in statistical methods is not as widespread in astronomy. Too often, models are assumed to describe observations even when there is no agreement between the two. To improve this, we propose a practical framework for assessing the consistency between observations and astrophysical models in a model-independent manner. The consistency test uses a...
ASTRON and S&T corporation are developing a detector of extreme solar radio bursts (SRBs). The aim is to provide real-time alerts and radio spectra from 3-3000MHz to KNMI and the Dutch military, so they can warn the Dutch vital economic sectors, as well as radio and radar operators of current radio interference due to the Sun. 70% of the first two phases of instrument development has been...
The observation of the far-IR 158 μm line of singly ionised carbon [CII] plays an important role in the study of star-forming regions of the interstellar medium (ISM) in galaxies. The connection between the [CII] fine-structure line and ionised phases of the ISM, could make [CII] emission a useful alternative star-formation rate (SFR) measure. However, due to the ambiguity of the origin of...
In 2019 the Event Horizon Telescope (EHT) delivered the first image of a black hole shadow in the center of the giant elliptical galaxy M87 and is expected to also produce high-resolution images of the supermassive black hole at the center of our Galaxy, Sgr A*. The latter is more challenging to image, being a short time-scale variable source and affected by the interstellar scattering. An...
The kinematics of molecular gas on cloud scales are a sensitive probe of the boundary conditions for star formation. Until recently, such measurements were only available for cloud populations within the Local group (including our own MW). But now, new survey capabilities are expanding our view of gas motions to a greater diversity of galactic environments, providing unprecedented constraints...
The detection of the faint 21-cm signal from the Epoch Reionisation (EoR) has been challenging due to strong foregrounds, ionospheric effects and radio frequency interference (RFI) etc. The precise calibration of data has been a key to the detection. Low frequency array (LOFAR) is a radio interferometer which is designed to detect the EoR. Over the years, the LOFAR-EoR team has been working on...
The Auger Engineering Radio Array (AERA) is an array of 153 radio antennas spanning an area of 17 km^2, currently the largest of its kind, that probes the nature of ultra-high energy cosmic rays at energies around the transition from galactic to extra-galactic origin. It measures the MHz radio emission of extensive air showers produced by cosmic rays hitting our atmosphere. The elemental...
The conditions under which the cold gas of galaxies evolves are not well known at higher redshift. The best way to understand cold gas is by studying the interstellar medium (ISM) of galaxies at different cosmic times. Far-infrared (FIR) emission lines are powerful tools for understanding the various phases of the ISM in galaxies. With this in mind, we have combined the cosmological EAGLE...
We present hydrodynamic simulations of the chemical evolution of the interstellar medium (ISM) gas influenced by the feedback from active galactic nuclei (AGN), coupled with the CHIMES code to treat the radiative cooling, AGN heating, and chemistry. We focus on the central 500 pc around the black hole (BH) where the AGN outflows and radiation couple to the ISM. In the simulation, we are...
CSS100217 was a nuclear flare in a Seyfert 1 galaxy, whose initial interpretation as a nuclear supernova is now debated between a tidal disruption event (TDE) and a flare from the active galactic nucleus (AGN). We discuss new evidence in favour of a TDE interpretation, mainly the marked difference in the optical quiescent flux before and after the outburst, as the post-outburst flux level is...
The gas and dust present within galaxies, known as the Interstellar Medium (ISM), is not homogeneous; star formation, supernovae events, as well as AGN activities may all greatly alter the ISM. In particular, recent studies of nearby external galaxies have shown that the molecular ISM varies at kiloparsecs as well as at parsec scales, with evidence of different gas components traced by...
Accreting black holes emit highly collimated radio jets expanding at speeds approaching light speed. Some of these jets appear to be expanding at superluminal speeds due to geometric effects. While magnetic fields are thought to be responsible for collimating the ejecta, the mechanism that accelerates the material in these jets remains unexplained. For the galactic black hole GRS 1915+105 with...
Understanding galaxy formation and evolution is one of the key goals of astronomical research. With roughly half of the galaxies in the local Universe residing in dense environments, it is therefore important to study the effects of environment on galaxy evolution. It has been known for several decades that galaxy clusters harbour a relatively large fraction of early-type galaxies, suggesting...
Non-spherical interstellar dust grains that are immersed in a magnetic field are expected to align with this field. The far-infrared (FIR) thermal emission of non-spherical grains is polarised along the longest axis of the grains. Combined, these two effects make polarised dust emission a powerful tool to study magnetic field configurations in environments where we expect a sufficiently strong...
The origin of most high-energy neutrinos is unknown. They have thus far been observed in coincidence with time-variable emission from three different types of accreting black holes: a gamma-ray flare from a blazar, an optical transient following a stellar tidal disruption, and an optical outburst from an active galactic nucleus. I propose a unified explanation for the latter two of these...
Galaxy mergers have been observed to trigger nuclear activity by feeding gas to the central supermassive black hole. One such class of objects are Ultra Luminous InfraRed Galaxies (ULIRGs), which are mostly late stage major mergers of gas-rich galaxies. Recently, large scale (∼100 kpc) radio continuum emission has been detected in a handful of ULIRGs, all of which also harbour powerful AGNs....
The isolated formation channel is one of the most studied formation scenarios for stellar mass black hole binary (BBH) mergers detected by LIGO and Virgo. Focusing on the effects of uncertain stellar and binary physics, we investigate this BBH formation channel using the rapid binary population synthesis code SeBa. Regardless of our assumptions, the two must common formation path within the...
The last phase transition of our Universe is Reionization, when the first galaxies emitted energetic photons that ionized the intergalactic medium (IGM). The escape of ionizing photons from complex galactic environments is a key process to understand Reionization. However, the opacity of the neutral high redshift IGM results in the need of indirect methods of studying ionizing photons. I will...
It is widely accepted that disc galaxies sustain their star formation by accreting gas from the external environment. In this study, we focus on one possible mechanism: hot CGM (corona) condensation triggered by the galactic fountain. Supernova feedback in star-forming galaxies continuously ejects out the plane part of the disc gas, which travels in the halo and falls back to the disc. This...
In the Unification Theory of AGNs the concept of “the torus” plays a crucial role to discern between Type-1 and Type-2 AGNs. Its emission, coming from hot and warm dust peaks at infrared wavelengths, which makes MATISSE an ideal instrument to observe it. The wide spectral coverage of the L, M and N bands, and the high spatial resolution that MATISSE offers, together with its capability to...
The nature and origin of magnetars is a key question across a range of research areas, from fundamental physics to transient astrophysics, where they have been invoked as the engines of a variety of transients including fast radio bursts. It is currently unclear whether magnetars are a common outcome of core-collapse events - only appearing rare due to their short active lifetimes - or if...
In the nearby (D=14 Mpc) AGN-starburst composite galaxy NGC 1068, it has been found that the molecular gas in the CND is outflowing, which is a manifestation of ongoing AGN feedback (García- Burillo et al. 2014). The induced interaction between the AGN ionized wind & jet with the molecular gas on the CND has produced large-scale molecular shocks on spatial scales of up to 400 pc from the AGN....
Weak gravitational lensing, the deflection of light rays caused by the inhomogeneous matter distributions, has been a powerful tool for observational cosmology. While promising in the application, it is demanding to measure the weak lensing signals to the desired accuracy in practice. With the ever-growing statistical powers of weak lensing surveys, it is critical to address any potential...
The burst energy distributions of repeating fast radio burst (FRB) sources are an important diagnostic of the emission process. To date, burst energy distributions have only been studied for a few active repeaters, and are limited both by telescope sensitivity (for the weakest and most common bursts) and on-sky time (for the brightest and rarest bursts). Though there is evidence for a...
Detecting cosmic rays using the radio emission generated in extensive air showers that form when cosmic rays interact in the atmosphere has proven to be a highly effective technique. Existing radio telescopes can detect this signal, and the dense antenna spacing of the LOFAR telescope and the upcoming SKA telescope make these instruments ideal to probe the features of radio emission in great...
On June 13 2022 Gaia Data Release 3 will be made public. This release will feature a major increase in the availability of astrophysical information on sources throughout the Milky Way, including stellar parameters and abundances (some 500 million sources), spectra for some 220 million sources, and parameters of variable and binary stars, among many other new data products. I will provide a...
I discuss briefly the current status of JWST commissioning and the planning of the first cycle
The relation between half-light radius and galaxy stellar mass has in recent years been studied extensively using large photometric surveys. This scaling relation has been found to be different for early types and late types, with different logarithmic slopes and zero points, and to evolve with time. While it provides important clues as to the assembly history of galaxies, the interpretation...
The cool and dusty circumstellar envelopes of asymptotic giant branch (AGB) have for a long time been modelled assuming a spherical symmetry. High spatial resolution observations of these stars have shown that their surroundings exhibit a variety of complex structures. Most of these structures are believed to originate from the interaction of the AGB wind with an obfuscated, nearby, orbiting...
A common method to determine the physical properties of protoplanetary disks is to analyse their spectral energy distributions (SEDs). However, the results are well-known to be degenerate. Running a full Bayesian analysis that can address this problem is challenging due to the high computational cost of full radiative transfer models. In my talk, I will show how we successfully train Neural...
The formation of ultra-diffuse galaxies is one of the most actively discussed subjects in extra-galactic astronomy during the last years. Yet, no clear consensus has been reached regarding their evolutionary pathways, with a number of simulations producing UDG-like galaxies using very different feedback prescriptions and even with different dark matter haloes properties. In order to test such...
Prominences are cool, dense plasma clouds found in the optically thin solar corona, which makes them classical examples of condensations due to thermal instability. The levitation-condensation mechanism has been used in simulations to explain prominence formation in a flux rope, which is created through shearing and converging motions of coronal loop footpoints. These simulations employ two...
While the general properties of the very low surface brightness galaxies with large effective radii (recently been dubbed "Ultra Diffuse Galaxies" or "UDGs") were once thought to be a challenge for the existing models of galaxy formation, the triumph of recent models in reproducing these properties erases most of the raised concerns in our understating of galaxy formation...
The extreme contrast ratios between stars and their planets at optical wavelengths make it challenging to isolate light reflected by exoplanet atmospheres. Yet, these reflective properties reveal key processes occurring in the atmospheres, and also span wavelengths that include potential O2 biosignatures. High resolution cross-correlation spectroscopy (HRCCS) offers a robust avenue for...
I will present my group's work on exploiting ongoing Gaia data releases to constrain the hardly observable properties of our own Galactic Center exploiting rare unbound stars, that are ejected from the vicinity of SgrA* and travel on unbound orbit through the Milky Way Halo.
We present a detailed chemical abundance analysis of the YMC NGC 1569-B. The host galaxy, NGC 1569, is a dwarf irregular starburst galaxy located 3.4 Mpc away. We derive abundances of the α, Fe-peak, and heavy elements. Abundance ratios were determined from the analysis of an optical integrated-light spectrum of NGC 1569-B, obtained with the HIRES echelle spectrograph on the Keck I telescope....
Galaxies are an amalgamation of several components (dark matter, stars, gas, and dust), constantly interacting with one another. This interaction is imprinted on the spectral energy distribution (SED) of a given galaxy. Panchromatic SED fitting can shed light on the astrophysical processes that regulate galaxy evolution. However, the current SED modeling approaches come with many caveats and...
Ultra-hot Jupiters have dayside temperatures at which most molecules are thermally dissociated. The dissociation of water vapour results in the production of the hydroxyl radical (OH). We report on the detection of OH in the atmosphere of the ultra-hot Jupiter WASP-76b using high-resolution transmission spectroscopy with CARMENES. Our detection shows that water is indeed being thermally...
Gaia eDR3 (and soon DR3) has revealed a number of kinematic groups in the solar neighbourhood. Some of these are now well know major accretion events such as Gaia-Enceladus-Sausage and Sequoia. Other smaller groups have been identified and their nature is not fully understood. Here I will present a method to extend the local spectroscopic sample by extrapolating the orbits of less-prominent...
An Astronomy Project for children with disabilities and underserved communities around the world
Stars Shine for everyone Project is a cooperation between UGent Volkssterrenwacht Armand Pien and Ghent University, started in 2015. Purpose of the project: ” To give children in special education and vulnerable people the opportunity to admire the starry sky with the help of a telescope.”...
The public observing nights at the Anton Pannekoek Institute are fully booked every month. With the arrival of corona, we moved our events online, like so many others. This served those who were interested in theory, but not those who came to us because they wanted a glimpse of the night sky through a real telescope. To still be able to serve (and expand) this part of our audience, we teamed...
I will share updates on efforts to promote inclusion and diversity in astronomy from the European Astornomical Society Advisory Committee on Diversity and Inclusion , and the International Astronomical Union Executive Committee Working Group on Equity and Diversity in Astronomy. I will discuss current activity, implications and connections for Dutch and Belgian Astronomy, and how to become...
I will share updates on efforts to promote inclusion and diversity in astronomy from the European Astornomical Society Advisory Committee on Diversity and Inclusion , and the International Astronomical Union Executive Committee Working Group on Equity and Diversity in Astronomy. I will discuss current activity, implications and connections for Dutch and Belgian Astronomy, and how to become...
The SKIES project is part of Horizon 2020 funded by the EU, and aimed to provide training on innovation, entrepreneurship and open science topics to Dutch astronomy PhD students and early-career researchers in combination with an individual mentoring programme. The training course was developed in collaboration with research institutes in Germany, Poland, Portugal, South Africa and external...
The current state-of-the-art cosmological simulations do not treat dust physics. Given the significant impact of dust on the observables, this is done at a post-processing stage. A number of post-processing studies using the SKIRT radiative transfer code have shown that the UV broadband fluxes and IR colors are a source of tension with observational data. Various reasons have been attributed...
M-dwarfs are thought to be hostile environments for exoplanets. Stellar events are very common on such stars. These events might cause the atmospheres of exoplanets to change significantly over time. It is not only the major stellar flare events that contribute to this disequilibrium, but the smaller flares might also affect the atmospheres in an accumulating manner. In this study, we aim to...
We present a robust representation of the galaxy group NGC 5813's chemical and thermal structure analysing archival, deep X-ray observations of the group using up to date atomic line emission models and multi temperature spectral model. The selection of our target is motivated by the fact that NGC 5813 has a very relaxed morphology, making it a promissing candidate for the study of the AGN...
Following a close dynamical encounter with Sgr A, stellar binaries in the Galactic Centre (GC) can be tidally separated. One member star remains bound to Sgr A and the other is ejected as a hyper-velocity star (HVS) with a velocity beyond the escape speed of the Milky Way. The abundance and properties of these objects can provide insight into still-uncertain aspects of the stellar...
The total disk gas mass and elemental C, N, O composition of a protoplanetary disk are crucial ingredients for our understanding of planet formation. Measuring the gas mass is complicated as we lack the far-IR facilities necessary to observe HD, and the elemental abundances with respect to hydrogen are degenerate with gas mass in all disk models. We determined the gas mass and elemental...
In this talk, I will discuss results from radio timing observations of the black widow binary pulsar J0610-2100 and optical observations of its binary companion. The radio timing observations extend the timing baseline to 16 yr and reveal a marginal detection of the orbital period derivative, but they show no significant evidence of orbital variations such as those seen in other black widow...
The state of the neutral interstellar medium critically affects the galactic star formation process and baryon cycle. Cosmological simulations which emulate galaxy evolution for a statistical sample of galaxies typically do not consider the transition of atomic to molecular hydrogen in the cold neutral medium. To compare the simulation output to observations, the atomic and molecular fractions...
We present central stellar velocity dispersion measurements for 158 type 1 AGNs from the second data release of the Swift/BAT AGN Spectroscopic Survey (BASS DR2) with a redshift cut-off z < 0.08. A total number of 297 type 1 AGN spectra are fit for obtaining two independent measurements from the Ca II H+K + Mg I region (3880 - 5550 ̊A) and the calcium triplet region (8350-8750 ̊A). The...
Atmospheric dispersion, the wavelength dependent differential refraction of light passing through the atmosphere, will cause severe degradation of image quality and contrast on the upcoming Extremely Large Telescope (ELT). Although the effect is the most severe at short wavelengths and low observing altitudes, the high resolution of the ELT causes atmospheric dispersion to be a problem well...
Since the day of its explosion, supernova (SN) 1987A has been closely monitored to study its evolution and to detect its central compact relic. In fact, the formation of a neutron star is strongly supported by the detection of neutrinos from the SN. However, besides the detection in the Atacama Large Millimeter/submillimeter Array (ALMA) data of a feature that is somehow compatible with the...
Relatively massive galaxies such as the Milky Way are expected from theoretical galaxy formation and cosmological simulations to contain a hot gas corona extending to roughly the virial radius. In the Milky Way the existence of this hot corona has been established mainly relatively close to the galactic disc through observations in absorption and X-ray emission. Most constraints on the density...
For its numerous effects on the evolution of a galaxy, dust has been studied in detail ever since its discovery. Visible in emission in the infrared regime, its spectral energy distribution is a powerful tracer of many properties, when fit by physical dust models. There remains however a property of dust grains that has not yet been poked at extensively, potentially retaining some crucial...
The recent MeerKAT deep surveys in the nearby Universe opened a new era of investigation of the neutral atomic (HI) gas in nearby galaxies. By reaching high spatial and spectral resolution with short observations, along with a large field of view (~1 degree), MeerKAT now enables us to investigate the presence of low-column density (~1x10^18 cm^-2) HI in all types of galaxies in different...
Large amounts of gas and dust are found in the central regions of most active galaxies. These ambient media play a crucial role as they provide the accretion reservoir powering AGNs and reprocess the X-ray, UV and optical emission of the central engine. Yet, the detailed characteristics of these regions and the physics behind them remain unknown. Recent radiative transfer modelling suggests...
Water ice has been found to be ubiquitous in quiescent molecular clouds and star-forming regions. It is formed on the surface of tiny dust grains located in cold environments (~10K). Satellite missions have concluded that water enters protoplanetary disks mostly as ice, and may later be delivered to planets. This emphasizes the need of knowing the basic properties of water ice, which will be...
Protoclusters are progenitors of galaxy clusters at the present day and are important for studying how halo mass and stellar mass assemble in the early universe. Tracing signposts that are expected to live in dense regions is a widely adopted method to identify protoclusters. Bright dusty star-forming galaxies (DSFG) are one of these signposts. Hyperluminous infrared galaxies (HLIRGs), which...
Recently an unexpected UV afterglow was reported for the Fast Blue Optical Transient AT2018cow. The most supported explanation for this event is currently a peculiar supernova, although other theories cannot be ruled out. Supernovae are expected to become redder over time, and not much research has gone into potential UV afterglows of such events. We investigate whether there are UV afterglows...
KiDS, the Kilo-Degree Survey, has mapped the distribution of dark matter using gravitational lensing. The final 'Legacy' analysis is underway, but results based on 2/3 of the data are available and provide interesting tests of the standard Lambda-CDM model of cosmology, including intriguing discrepancies. I will discuss these results as well as look forward to the improvements that can be...
The KiloDegree Survey has proven to be a fertile training ground in preparation for Euclid, ESA's satellite to study the nature of dark matter and dark energy. In this talk I present some recent highlights from KiDS, with a focus on how observations can be used to account for astrophysical sources of bias, thus improving the fidelity of current and future constraints on cosmological parameters.
The first population of X-ray binaries are expected to affect the thermal and ionization states of the gas in the early Universe. Although these X-ray sources are predicted to have important implications for high-redshift observable signals, such as the hydrogen 21-cm signal from cosmic dawn and the cosmic X-ray background, their properties are poorly explored and theoretical models are...
Observations of the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and Reionization epochs promise to provide valuable insights into the (astro)physical processes that governed the structure formation in the early Universe. The AARTFAAC wide-field imager of the LOFAR telescope is an excellent instrument to measure the redshifted 21-cm signal on large angular scales from the...
Before the end of the epoch of reionization, the Hydrogen in the Universe was predominantly neutral. This leads to strong attenuation of Lyman alpha lines of z>6 galaxies in the intergalactic medium. Nevertheless, Lyman alpha has been detected up to very high redshifts (z~9) for several especially UV luminous galaxies. Here, we test to what extent the galaxy's local environment might impact...
The coupling between radio and X-ray luminosity is an important diagnostic tool to study the connection between the accretion inflow and jet outflow for low-mass X-ray binaries (LMXBs). Moreover, the comparison of NS- and BH-LMXBs provides useful information about the role of compact objects in launching jets. Interestingly, studies have shown discrepancies between the radio-X-ray coupling of...
Circumstellar discs are found at different evolutionary stages of stars. In this talk, I will focus on a class of evolved stellar systems that show stable circumbinary discs of gas and dust, namely post-asymptotic giant branch (post-AGB) binary systems. These circumbinary discs show remarkable, but unexpected, similarities with planet forming discs around young stellar objects. Using infrared...
Planetesimal formation in protoplanetary disks is still one of the major open questions in planet formation theory. It is known that solids can’t grow up to asteroid size relying on sticking after pairwise collisions only, due to the fragmentation barrier and the drift barrier. A possible solution is to form dense particle clumps, with low velocity-dispersion, that can then collapse under...
