4MOST is a new high-multiplex, wide-field spectroscopic survey facility under construction for ESO's 4m-VISTA telescope at Paranal, Chile. Its key specifications are: a large field of view of 4.4 square degrees, a high multiplex fibre positioner with 2436 science fibres, of which 1624 fibres go to two low-resolution spectrographs (R = λ/Δλ ~ 6500) and 812 fibres transfer light to the...
Ionization plays a critical role in the gas dynamics of protoplanetary disks (PPDs), which is further related with disk evolution and planet formation. While non-thermal ionization mechanisms, such as X-rays and cosmic rays, dominate the bulk regions of PPDs, the innermost regions are characterized by high temperatures (>1000K) with thermal ionization of alkali species and dust thermionic...
Collisions and interactions between galaxies are thought to be crucial phases in their evolution and mass assembly process, elevating star formation activity and potentially fueling accretion onto the central supermassive black holes. In this study, we leverage the high spatial resolution and sensitivity of the Hyper Suprime Cam survey and the associated rich multi-wavelength data in the GAMA...
The broad line region of active galactic nuclei, tightly connected to the central engine's activity, is still poorly understood. In this talk, we present an analysis of X-ray, UV and optical spectroscopic observations of the broad emission lines applied for the first time to a narrow-line Seyfert 1 (Juranova et al., to be subm.). For the panchromatic modelling of the broad-line emission, we...
In astronomy, machine learning has succeeded in various tasks, such as source localization, classification, anomaly detection, and segmentation. However, feature regression remains an area with room for improvement.
We aim to design a network that can accurately estimate sources’ features and their uncertainties from single-band image cutouts. The algorithm presented here,...
Next-generation weak gravitational lensing surveys, including Euclid, will be able to measure weak lensing signals with high statistical accuracy all the way into the regime probing the scales of non-linear collapse. To be able to exploit these measurements to the fullest extent and, in the end, most accurately determine the cosmology, we must have an accurate understanding of the baryonic...
We present two independent measurements of stellar velocity dispersions ( $\sigma_\mathrm{\star}$ ) from the Ca H K & Mg I region (388--555 nm) and the Calcium Triplet region (CaT, 835--875 nm) for 173 hard X-ray selected Type 1 AGNs from 105-month Swift-BAT catalog. We construct one of the largest samples of local Type 1 AGNs that have both single-epoch (SE), 'virial' black hole mass...
Are you considering a career change and would you like to remain closely involved in scientific research but from a different perspective? Maybe working at NWO, the Dutch research council, is something for you! NWO welcomes new employees with a scientific background to facilitate the funding of outstanding research and to help define strategies for funding research. Become a programme...
Galaxy mergers and accretions are a fundamental process in galaxy evolution. In the Milky Way, we can identify signatures of past galaxy accretion events as kinematic substructures, allowing us to characterize the property of each accreted galaxy and, potentially, its impact on the Milky Way's evolution. We here characterize the chemical properties of stars belonging to kinematic substructures...
We present results obtained by the Isaac Newton Telescope Wide Field Camera in March and April 2023 as part of a graduate class from Rijksuniversiteit Groningen. We present results from projects designed by the master students including: strategies to obtain a chromosome map of the globular cluster GCL38, a method to potentially determine metallicities making use of photometry and...
This presentation shows the status of the construction of the Extremely Large Telescope. It addresses both the infrastructure (telescope and building), as well as the instrument suite.
Images and graphics show the assembly status of the Dome and Main Structure on site in Chile, and the development of the mirrors and optomechanical control systems. Key figures are presented. Contracts...
Accretion is a fundamental astrophysical process, occurring across all scales of black hole mass. Despite its ubiquitous nature, the accretion process, alongside its connection to jet outflows, poses many fundamental questions. General Relativistic Magneto hydrodynamic (GRMHD) simulations are providing significant insights into the nature of black hole accretion and jet outflows. Following...
GRS 1915+105 regularly shows type-C quasi-periodic oscillations (QPOs) in the power density spectrum, sometimes together with a broad bump at around 30-150 Hz. We study the power spectra of GRS 1915+105 with the Rossi X-ray Timing Explorer when the source was in the hard-intermediate state. We find that the rms amplitude of the bump depends strongly upon both the frequency of the type-C QPO...
The distance of the outflowing wind is poorly constrained due to lack of direct imaging observations, which limits our understanding of their kinetic power. One way is that once known the density of the ionized plasma, the distance can be derived from the ionization parameter which measured based on the ionization states. Here, applying a new time-dependent photoionization model, TPHO, in...
We present the discovery of an AGN remnant associated with the galaxy group Abell 1318. Using GMRT and APERTIF data, we derive its radiative age and disentangle its complex history, showing that galaxy groups can have (surprisingly) dynamic past.
ED-2 is a stellar stream identified in integrals of motion on the third Gaia data release. It forms a compact group in energy and angular momentum in a local sample (<3 kpc), and its stellar population resembles one of an old metal-poor simple stellar population. It forms a compact group in the R-z (or x-z) plane, showing a ribbon-like structure in the solar neighbourhood, crossing the Sun's...
The Event Horizon Telescope (EHT) has recently published the first images of the supermassive black hole at the center of our Galaxy, Sagittarius A$^\ast$ (Sgr A$^\ast$ ). Imaging Sgr A$^\ast$ is plagued by two major challenges: variability on short (approximately minutes) timescales and interstellar scattering along our line of sight. While the scattering is well studied, the source...
The release of Gaia DR3 has substantially enriched our understanding of the current state of the Milky Way (MW), and its assembly history. A driving force behind this is the increase of stars with complete 6d phase space (positions and velocities) necessary for complex dynamical analysis, such as identifying stellar substructures in the MW's stellar halo. However, far more stars are still...
Comparison of horizon-scale observations of Sgr A and M87 with numerical simulations has provided considerable insight in their interpretation. Most of these simulations are variations of the same physical scenario consisting of a rotation-supported torus seeded with poloidal magnetic fields. This setup has several well known limitations, most notably, it differs in important ways from what...
Using stellar models from BPASS population synthesis, we calculate the full GW spectrum of a stellar population, including all types of compact binaries as well as those with living stars. We use these results to look at the detectability of star clusters with LISA. We find at late times the dominant sources are WD–WD binaries, but surprisingly at earlier times we find a significant population...
A key characteristic of some active galactic nuclei (AGN), such as radio galaxies, is that they possess powerful jets that can extend through or beyond their host galaxy. However, the exact mechanisms of their launch and their internal properties are still not well understood. In this talk, I will focus on Event Horizon Telescope (EHT) and multi-wavelength image and spectral observations of...
Upcoming surveys such as the Legacy Survey of Space and Time (LSST) will image billions of galaxies to extract the faint weak lensing signal for cosmological parameter inference. A pressing issue is that 50% of the galaxies will be “blended”, where its projection on our detectors will overlap with other astronomical objects along the same line of sight. Without appropriate “deblending”...
We report low-frequency radio observations of the 2021 outburst of the recurrent nova RS Ophiuchi. These observations include the lowest frequency observations of this system to date. Detailed light curves are obtained by MeerKAT at 0.82 and 1.28 GHz and LOFAR at 54 and 154 MHz. These low-frequency detections allow us to put stringent constraints on the brightness temperature that clearly...
After the Dark Ages, when the universe was completely neutral, the first sources of light appeared, marking the beginning of the Epoch of Reionization (EoR). During this epoch, the first stars and galaxies formed, emitting intense radiation that ionized the surrounding neutral hydrogen gas, creating ionized regions in the intergalactic medium (IGM), which grew and overlapped, making our...
I will present new results from two MeerKAT Large Survey Programs - The MeerKAT Fornax Survey (MFS) and MHONGOOSE. The exquisite combined sensitivity and resolution of the MeerKAT telescope has opened the door to exploring the realm of resolved, low column density (10^17 - 10^18 cm^-2) neutral hydrogen (HI) emission in a broad range of environments. In the Fornax cluster, we detect (and...
Recent observations of high redshift galaxies are unveiling unexpected properties of early galaxy-formation. Observations in both rest-frame ultraviolet with the James Webb Space Telescope and rest-frame far-infrared with the Atacama Large Millimeter Array suggest an early population of bright massive galaxy, with a significant dust-obscuration already at redshift 7. To better understand the...
We couple the DELPHI framework for galaxy formation with a model for the escape of ionizing photons to study both its variability with galaxy assembly and the resulting key reionization sources. In this model, leakage either occurs through a fully ionized gas distribution (ionization bounded) or additionally through channels cleared of gas by supernova explosions (ionization bounded + holes)....
The physical properties of the faint and extremely tenuous plasma in the filaments of the cosmic web remain one of the biggest unknowns in our story of large-scale structure evolution. The most common techniques how to observe this medium are either in emission, or in absorption against very bright, point-like sources. In this talk I focus on the warm-hot intergalactic medium and present yet...
The Decameter radio band (< 30 MHz) has been scarcily explored since the inception of radio astronomy, largely due to the perturbing effects of the ionosphere. However, the decameter wavelength band is an important part of the electromagnetic spectrum. In particular, decameter observations of radio halos in galaxy clusters will allow us to constrain the particle reaccerlation mechanisms...
While from a classical perspective we think of vacuum as empty space, it is filled by virtual particles from a quantum perspective. In flat spacetimes, these virtual particles arise in pairs, exist for a short amount of time, and then re-annihilate. As a result, no real particles are created.
In this talk, we show that real particles are created in curved spacetimes. This is because...
Habitable Worlds Observatory is a next-generation space telescope started by NASA following the recommendation of the US astronomy decadal survey in 2021. It will combine the key features of LUVOIR-B and HabEx projects and promises to provide unprecedented capabilities for exoplanetary science and astrophysics. As a continuation of our study for LUVOIR-A project, we propose a European-led,...
Polycyclic aromatic hydrocarbons (PAHs) are very stable molecules made of aromatic carbon rings. Their prominent infrared features were found in interstellar space, in asteroids, and are one form of carbon in circumstellar disks. Even though they are not the dominant form of carbon, these molecules can be easily observed making them an object of active research interest. Professor Carsten...
Cosmological simulations have been used to understand the formation of structure in the ΛCDM paradigm on small and large scales. Most simulations start with unconstrained Gaussian initial conditions, and therefore generically do not produce good analogues of the Local Group at present day. While constrained simulations exist, these have difficulty in precisely satisfying all our observational...
In recent decades, numerous telescopes have been built to identify transients and periodic variables in the night sky. These telescopes have provided a boom in our understanding of the wide variety of transients and their progenitor systems in many astrophysical contexts. While the Northern hemisphere has enjoyed several dedicated telescopes observing both transient and periodic phenomena 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 extragalactic origin. It measures the MHz radio emission of extensive air showers produced by cosmic rays hitting our atmosphere. The elemental...
We develop a new technique to resolve small-scale structures in galaxy groups and clusters using XMM-MOS. This study takes advantage of the steep nature of the on-axis XMM PSF which encloses ~60% of the incident photon energy within 10 arcsec. Standard pipeline processing of XMM-MOS data yields images with 4 arcsec binning by default; however, images may be created with 1 arcsec bins to better...
Determining the circular velocity curve of a galaxy is a powerful tool for studying its overall shape. One can fit a potential and determine the dark matter distribution and density, or even the virial mass of the system.
One way of determining the rotation curve is through Jeans equations (Eilers et al. 2019, Ou et al. 2023). However, when using Jeans equations one needs to assume...
Anomalous flux ratios between lensed images can provide a key test of the dark matter sub-halo population, and hence the properties of dark matter particles. However, the observed anomalous flux ratios at radio frequencies can also be the result of systematics associated with our lack of knowledge about the source structure, source variability, and propagation effects within the lensing...
Hot-rocky exoplanets with surface temperatures above 1500 K are thought to support magma oceans. The presence of these magma oceans offers a unique opportunity for inferring the interior composition of these planets through the characterization of their atmosphere. With hundreds of hot-rocky exoplanets discovered and a dozen of good targets for JWST characterisation, understanding the links...
The spatial distribution of matter on the mega-parsec scale of the Universe forms a complex and highly anisotropic pattern termed the Cosmic Web or the Large-Scale Structure. In the study of the Cosmic Web, several tools and methodologies have been developed to inspect the properties of its different environments i.e. clusters, filaments, walls, and voids. In this work, we show that the...
With Gaia we have a thousand-fold increase in the number of stars and the precision with which we can observe their motion, which allows us to see previously rare phenomena in great numbers and detail. Astrometric binaries are a fantastic example of this - around half of all stars are binaries and precise astrometry enables us to detect a large fraction of these, with periods from months to...
Supernova (SN) feedback plays a fundamental role in galaxy evolution. However, modelling SN feedback in simulations of galaxy formation remains challenging because the simulations cannot resolve the scales on which SN feedback occurs. Therefore, SN feedback is generally implemented as a subgrid model that has a number of free parameters, which are calibrated such that the simulated galaxies...
Fast Radio Bursts (FRBs) are millisecond-duration transient sources of intense, coherent radiation originating in distant galaxies that are signposts of extreme astronomical environments. Telescopes all over the world are used to conduct searches for FRBs, localise them, and study their host galaxy and local environment. The European VLBI Network in particular is a prime instrument to study...
Runaway stars (massive stars moving away from the star clusters where they were born at unusually high velocities) have been observed for more than half a century, yet the origins of these high velocities remain elusive to this day. One of the most prominent theories for the origins of runaway stars is the dynamical ejection scenario in which binaries are thought to dynamically interact with...
High energy neutrinos(>10PeV) are integral to the multi-messenger astronomy and notoriously hard to detect. When a high energy neutrino interacts in ice, it produces a relativistic cascade of charged particles, which in turn leaves behind a plasma which can reflect radio waves. This is the concept of the Radar Echo Telescope (RET). But as a first step it's important to understand the method by...
The evolution of stars on grand time-scales affect their surroundings in many ways. Due to their intrinsic rotation, causing strong magnetic activity, they vary greatly in radiative activity in X-ray and ultraviolet (XUV) throughout their lifetime. Planets orbiting these stars close-in could, consequently, be affected by these drastic radiative changes. Close-in exoplanet atmospheres heat up...
The high angular resolution and sensitivity of VLBI offers a unique tool to identify and study AGN and star-formation activity. Radio imaging across a large range of angular scales is needed to determine the role of black hole feedback and jet-induced star formation in galaxies. All-sky VLBI surveys can answer these questions and find rare radio sources, such as gravitational lenses. Despite...
Supermassive black holes experience dynamical friction, a drag force caused by momentum exchange with the surrounding medium of stars, dark matter, and gas. In this study, we investigate dynamical friction on massive black holes in depth, including testing a commonly used analytic model based on Chandrasekhar's 1943 study. Our goal is to develop a functional subgrid model that can be...
Recent Event Horizon Telescope (EHT) observations of M87 and Sgr A have proven to be an insightful data set to probe the spacetime and physical conditions in accreting supermassive black hole systems. For this purpose an ad hoc and fixed, pre-computed library of ~60,000 model images for M87 and about 1,800,000 for Sgr A was used to sample black hole spin, magnetic flux on the horizon,...
X-ray binaries, which are neutron stars or black holes accreting gas from a companion star, emit radiation across the electromagnetic spectrum. Whereas it is well established where their X-ray and radio emission originates, it is much less clear where their infrared emission comes from: is it coming from the cooler outer part of the disk, the companion star, a jet, or a hot flow? During my...
Unveiling the mechanisms that trigger active galactic nuclei (AGN) is a badly understood problem, that is crucial for our understanding of the galaxy formation and evolution. While interactions and galaxy mergers are associated with the triggering of powerful AGN, less luminous AGN would be driven by secular processes (Treister et. al., 2012). Over the last few years, several observational...
At Leiden University's radio astronomy course, we observe the Milky Way using radio telescopes made of 5 litre paint cans, commercial Low Noise Amplifiers (LNAs) and Software Defined Radios (SDRs). Galactic neutral hydrogen can be detected on student's own laptops in mere seconds! This experiment involves the whole process from systems engineering, through signal processing, field experiments,...
The characteristic mass that sets the peak of the stellar initial mass function (IMF) is closely linked to the thermodynamic behaviour of interstellar medium (ISM), which controls how gas fragments as it collapses under gravity. As the Universe has grown in metal abundance over cosmic time, this thermodynamic behaviour has evolved from a primordial regime dominated by molecular hydrogen...
Wide-field Spectroscopic Telescope (WST) is a project of a next generation 10m-class telescope intended for spectroscopic surveys. It will include a multi-object spectrograph (MOS) unit covering a large field from 2.5 to 5 square degrees and providing medium (up to R7000) and high (R40 000) resolution spectra in the range of 360-1300 nm with a high multiplex of 20 000 and 2000, respectively....
A new era of high-resolution X-ray spectroscopy is upcoming. This spring, the JAXA/NASA (with SRON/UniGe/ESA participation) XRISM mission will be launched.
As already revealed by the short-lived Hitomi mission, the new vision on an energy band never explored before at high resolution, will bring transformational results.
In particular, the X-ray calorimeter, Resolve, will bring new insight...
Fast radio bursts (FRBs) are enigmatic astrophysical transients; they are brief, intense flashes of radio emission from extragalactic sources. The extreme brightness and millisecond-duration timescales of FRBs indicate that they are likely produced by compact objects with large energy reservoirs, such as accreting black holes or magnetars (ultra-magnetic neutron stars). Although most FRBs...
Radio observations are excellent probes of the environmental conditions in the coronae/magnetospheres of stars and brown dwarfs. In particular, radio emission traces the impact of stellar plasma on exoplanet atmospheres, the processes of coronal heating, and key parameters for assessing exo-habitability. The strong magnetic field of these stellar systems leads to radio emission via different...
Massive stars are the progenitors to a vast variety of observed highly energetic transients. Many of these transients are presumably the product of interaction between two or more stellar companions. Until recently, theoretical work has mainly focused on understanding the evolution of single- and binary stars. However, recent observations show that triple (and higher order multiple) star...
