Direct observation of the Cosmic Dawn and Epoch of Reionization via the redshifted 21-cm line will have unprecedented implications on the study of structure formation in the early Universe. This exciting goal is challenged by the difficulty of extracting the feeble 21-cm signal buried under bright astrophysical foregrounds and contaminated by numerous systematics. The LOFAR-EoR and NenuFAR...
The source count dipole from wide-area radio continuum surveys allows us to test the cosmological standard model.
Many physical radio sources are observed as multiple components, which can cause an overdispersion of the source counts distribution.
We account for this effect via a new Bayesian estimator, based on the negative binomial distribution.
Combining the two best...
The faint radio-source population includes sources dominated both by star formation and active galactic nuclei (AGN), encoding the evolution of activity in the Universe. Investigating its nature requires accurately identifying the dominant source of emission in each system - a task that spectroscopy is uniquely well-suited to address. To demonstrate this, we make use of available spectra...
Lyα emitters (LAEs), characterized by their prominent Lyα emission at 1216 Å, are key tracers of high-redshift galaxies and play a crucial role in our understanding of galaxy evolution and cosmic reionization. In particular, radio-detected LAEs offer valuable insights into the interplay between star formation, active galactic nuclei (AGN) activity, and the interstellar medium.
Using the...
In this talk we explore the intricate role of both galaxy-intrinsic and environmental factors in triggering radio AGN activity in the local Universe. We investigate the prevalence of radio AGN by combining radio observations from the LOFAR Two-Metre Sky Survey (LoTSS) data release 2 with optical data from the extensively characterised Sloan Digital Sky Survey (SDSS). The large samples allow us...
There are still many open questions and uncertainties regarding the evolution of radio galaxies. Compact AGNs, such as Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources, are thought to be the precursors of classical double-lobed radio galaxies. However, some studies suggest their evolution may be more complex than previously assumed. These sources can be temporarily...
Very-long baseline interferometry (VLBI) across a wide field of view is notoriously difficult given the extreme data volume and compute resource requirements. Nevertheless, improvements in the calibration and imaging algorithms in the past few years made it possible to carry out wide-field imaging at sub-arcsecond resolution using the LOFAR High-Band Antenna (HBA).
The strong variations of...
Radio relics are elongated diffuse sources located in the outskirts of merging galaxy clusters, tracing merger-induced shocks. In the last decade, high-resolution observations - up to a fraction of an arcsecond - at GHz frequencies have revealed that they are characterized by filamentary structures, challenging our understanding of these sources.
In this talk, I will present the first images...
LOFAR surveys have enabled unprecedentedly detailed analysis of large-scale, diffuse, and steep-spectrum sources in galaxy clusters, such as radio relics and halos. These are thought to arise from particle re-acceleration operated in the intra-cluster medium (ICM) by shocks and turbulence triggered by a cluster merger. Similar processes are likely also responsible for the re-ignition of fossil...
The Universe hierarchical formation process can be investigated through the fundamental relations of galaxy cluster observables. Since the matter accretion is gravity-dominated, the hot plasma within galaxy clusters displays a self-similar behaviour, following precise scaling relations that link spatially resolved quantities to global ones. Similarly, the diffuse, non-thermal cluster component...
Radio halos are large-scale, diffuse radio sources with low surface brightness located in the central regions of galaxy clusters, extending across several megaparsec scales. They are believed to originate from cosmic rays re-accelerated by merger-induced turbulence by second-order Fermi mechanism. The turbulent re-acceleration model anticipates a substantial population of radio halos with...
Magnetic fields are ubiquitous, permeating all large-scale cosmic structures — voids, filaments and galaxy clusters — and their strength decreases with thermal electron density. Understanding magnetic fields in the transition regions between clusters and filaments is crucial for unravelling the interplay of thermal and non-thermal processes and the mechanisms that amplify weak seed fields....
By the end of LOFAR 1.0 operations in the summer of 2024, the LOFAR Two-meter Sky Survey (LoTSS) had surveyed 85% of the Northern sky. The majority of the missing 15% of regions are at Galactic latitudes b<|20| degrees. However, a substantial fraction of the Milky Way was observed as part of the LoTSS, and will be part of data release three (DR-3), including two long contiguous segments...
Planetary nebulae are gaseous shells ejected by low-mass stars at the end of their lives. The shells are ionized by hot central stars. The ionized plasma is a source of thermal radio continuum emission at GHZ frequencies with a spectral index between 0 and 2. This emission is spatially correlated with optical emission lines. LOFAR images revealed radio emission originating in many cases from...
Polarisation studies over a significant redshift range are an important tool for understanding the evolution of cosmic magnetic fields and unrevealing their origin. As most depolarisation effects are highly wavelength dependent, the combination of different surveys allows us to distinguish between different effects.
We use the synergy of LOFAR and Apertif; starting with sources known to...
Modern, large-area sky surveys at decametre to decimetre wavelengths have begun to reveal the widespread presence of magnetised plasma in the intergalactic medium, transported from SMBHs through relativistic jets. Even more sensitive surveys, such as those possible with LOFAR 2, the DSA-2000, and the SKA, will likely uncover many larger and older plasma deposits, from the Local Universe to the...
Blazars have been challenging to study at low radio frequencies due to limited sensitivity and resolution in previous surveys at these frequencies. However, the recent LOFAR surveys; LoLSS-DR1 and LoTSS-DR2, have addressed these issues enabling robust detection of known blazar counterparts. Utilising this, we examine the spectral properties of the blazar population at low frequencies. We...
In the radio regime, blazars are mostly compact sources. However, at low radio frequencies, we may observe large-scale (several hundred of kpcs) structures. In such a case, two different radio components make up the total radio flux: a flat-spectrum central element and steep-spectrum diffuse pair of lobes, sometimes irregular, plural or misaligned with the jet axis. We interpret their...
Peaked-spectrum (PS) radio sources - Gigahertz-Peaked Spectrum (GPS) and Megahertz-Peaked Spectrum (MPS) - are known to trace the youngest stages of jet evolution. Milliarcsecond VLBI images often reveal compact double morphologies embedded in kpc-scale cocoons, suggesting that many PS objects could later grow into classical FR II or FR I radio galaxies. A key open question is whether this...
The majority of baryonic matter in the Universe resides as plasma within the large-scale cosmic web, with galaxy clusters representing its densest nodes. These clusters grow through accretion and mergers, processes that inject substantial energy into the intracluster medium via shocks and turbulence. Low-frequency radio observations have revealed that these mechanisms accelerate particles to...
New generations of interferometers are revealing a wealth of spectacular filaments in the surrounding of radio galaxies, mostly residing in group/cluster environment, whose origin is still unknown. Filamentary structures present new opportunities for studying the physical processes in the intracluster medium, including their magnetic structures and the propagation of cosmic rays. Given the...
In this talk, I will present the first LOFAR LBA observations of the well-known galaxy cluster CIZA J2242.8+5301 (the “Sausage” cluster), reaching a thermal-noise limited sensitivity of 1.5 mJy/beam at 15″ resolution. This system is not only a benchmark for studying radio relics, but also one of the very few galaxy clusters observed with LOFAR LBA to date. The 45 MHz observations represent the...
The Perseus cluster is a nearby, well-studied cool-core galaxy cluster, known to host a radio mini-halo. Recent LOFAR HBA observations have revealed a Mpc-scale giant radio halo, enveloping the mini-halo. The origin of this extended radio emission and the underlying particle (re-)acceleration mechanisms remain poorly understood. By exploring the spectral properties of the radio emission at...
We present a joint analysis of the radio and optical morphological properties of LOFAR sources in the Euclid Deep Field North. Radio sources have been separated into AGN and star-forming galaxies and further subdivided according to their radio appearance (e.g. whether point-like or extended/complex). This information has then been complemented with Euclid/VIS images which provide a snapshot of...
The population of massive, dust-obscured galaxies plays an increasingly prominent role in the context of galaxy evolution. These galaxies are considered the progenitors of the passive systems observed at z~3, and they significantly contribute to the cosmic star formation rate (SFR) density at high redshift (z>3). Due to their faintness in optical and near-infrared (NIR) bands, a key challenge...
In this talk, I will present a systematic study of how large‐scale environment influences the triggering and evolution of radio AGN. Using LOFAR observations at 144 MHz, we cross‐match a sample of more than 200.000 AGN from LoTSS DR2 with optical group and cluster catalogs to define subsamples of field, group and cluster AGN. A spectroscopic subset is also classified into HERGs and...
Understanding how active galactic nuclei (AGN) evolve with cosmic time and interact with their host galaxies is central to constraining the role of AGN feedback in galaxy evolution. In the era of deep, wide-field sky surveys, it is now possible to statistically characterise the relationship between radio AGN activity and host galaxy properties across the full AGN population. We investigate the...
The wide-area LOFAR surveys combined with deep optical data offer an unprecedented opportunity to characterize and model the radio-luminous AGN population, which are thought to play an essential role in the evolution of the most massive galaxies. I will discuss the latest results on the selection of this AGN population and what we can learn statistically about host galaxies, environments and...
The Euclid Deep Field North (EDFN), located at RA=269.73 deg and
Dec=+66.02 deg in the North Ecliptic Pole (NEP) region, is the fourth
field of the LoTSS Deep Field project, and the only deep field in the
northern sky to be observed by the Euclid mission.
The Euclid satellite will cover the circular shape 20 sq deg of the
EDFN with multiple passes providing high-resolution near-IR...
The LOFAR Two-metre Sky Survey is a deep low frequency survey of the northern sky. We are preparing to release LoTSS-DR3 which consists of images and data products covering about 90% of the northern sky. These data products were created from 13,000hrs (or 19PB) of observations and took around 20 million CPU core hours to produce. The survey images contain over 13.7 million sources and...
We present two new radio continuum images obtained with Apertif at 1.4 GHz. The images, produced with a direction-dependent calibration pipeline, cover 136 square degrees of the Lockman Hole and 24 square degrees of the ELAIS-N fields, with an average resolution of 17x12" and residual noise of 33 uJy/beam. With the improved depth of the images we found in total 63692 radio sources, many of...
The LOFAR Low Band Antenna (LBA) system makes LOFAR the only telescope capable of ultra-low frequency (<100 MHz) observations at high resolution. Working at these frequencies is challenging due to the low signal-to-noise ratio and ionospheric disturbances. Developments in the calibration strategies allowed us to reach thermal noise and even attempt <30 MHz imaging and long-baseline...
LOTAAS, the LOFAR Tied-Array All-Sky Survey, offers an extensive dataset for discovering low-frequency radio transients. However, the original single-pulse search was not optimized to detect longer-duration or heavily scattered signals, and was limited by high false positive rates arising from instrumental variability and RFI. Since then, our understanding of FRBs at low frequencies has...
In recent years, the study of nearby galaxies at low radio frequencies has seen significant progress, largely driven by the capabilities of the Low-Frequency Array. Both targeted observations and wide-field surveys, such as the LOFAR Two-metre Sky Survey, have provided unprecedented insights into the properties of galaxies in the local Universe.
This talk will present the work of the LOFAR...
Radio continuum emission has the potential to be an extinction-free star formation tracer in galaxies near and far. Low-frequency radio continuum observations can give us new insights into the workings as well as the limitations of the radio-star formation rate (radio-SFR) relation. We used maps from a sample of nearby galaxies including both low- and high-band data from the LOw Frequency...
We present a detailed multi-frequency study of the resolved radio--far-infrared (FIR) correlation in the nearby spiral galaxy IC342 (3.3 Mpc), using new LOFAR 144 MHz observations and archival VLA data at 1.4 and 4.8 GHz, combined with Herschel PACS and WISE infrared maps. After isolating synchrotron emission via thermal/nonthermal separation using $22\mu$ m emission, we analyze spectral...
Since taking its first cosmic ray data in 2011, LOFAR has demonstrated the potential of radio measurements of cosmic ray air showers. With analysis techniques developed along the way, high-precision results on their primary energy and the depth of shower maximum became available, putting the radio technique in line with the state of the art in this field.
In this talk I will review the...
Have you ever been to the LOFAR superterp and noticed the black boxes spread across the grass there? In this contribution, I will give an overview of the particle detectors these boxes house, and the fundamental role they play in cosmic-ray detection at LOFAR.
When a cosmic ray enters the atmosphere it initiates a cascade of particles called an air shower. This cascade generates a sharp...
Radio transients in the image domain are currently undergoing a big revolution, with exciting new discoveries from radio telescopes around the World including from LOFAR. Key highlights from LOFAR include the detection of the first candidate coherent radio transient following a gamma-ray burst and the first identification of a source of the new class of long period Galactic transients.
In...
Long-period transients (LPTs) are a recently identified class of coherent radio transients with durations ranging from a few seconds to several minutes, and periodicities on timescales of minutes to hours. To date, only nine such sources have been reported, with few confirmed to reside in white dwarf–M-dwarf binary systems. The absence of detected optical companions or detection of X-rays in...
We recently opened a new window into the variable radio sky on timescales of seconds to minutes. Through these observations, a new class of sources Long Period Transients (LPTs) has begun to emerge. These transients emit previously unknown radio flares lasting from seconds to minutes and exhibit periodicities ranging from minutes to hours. Such timescales suggest that these transients produce...
Over the past decade, our understanding of fast radio bursts (FRBs) has greatly increased. We have now discovered thousands of these millisecond-duration, extragalactic bursts, and have localised over a hundred of them to their host galaxies. While at least some FRBs appear to come from the ultra-magnetised neutron stars known as magnetars, the diverse locations and properties of FRBs suggest...
The LOw-Frequency ARray (LOFAR) offers an unprecedented opportunity to study the magneto-ionised medium of the Milky Way. In this talk, I will present two mosaics constructed from the second data release of the LOFAR Two-Metre Sky Survey (LoTSS-DR2), which trace polarised synchrotron emission in the high-latitude inner and outer Galaxy. We associate the dominant observed structures with Loop...
Magnetic fields in dense starless cores are crucial for understanding the formation of stars, as these molecular cores mark the initial gravitationally bound stage in the star-formation process. Typically, these cores accumulate gas from their molecular cloud environment until they overcome magneto-turbulent support and collapse into protostellar objects. Traditional studies of magnetic fields...
The supernova remnant Cassiopeia A plays a unique role in radio astronomy and astrophysics and is currently being explored in various ways. We present recent developments in NenuFAR observations applied to Cas A at low frequencies. Beginning in 2019, the GURT one-baseline interferometer established the continuous radio spectrum of Cas A at 16–74 MHz, using Cyg A as a calibration source. Based...
In this talk, I will present our work with the data from the Long-Term 10 program of the newly commissionned NenuFAR telescope in Nançay. This program aimed at observing radio recombination lines (RRLs) between 10 and 85 MHz in absorption in various Galactic lines of sight. I will present the results we obtained observing towards Cassiopeia A, Cygnus A, and Tau A. For each of these lines of...
In recent years, we have established a robust strategy for producing sub-arcsecond (wide-field) images using the full European LOFAR array (Morabito et al. 2022; Sweijen et al. 2022). These high resolutions reduce confusion noise, making it possible to create ultra-deep images by combining multiple LOFAR observations. However, this comes for wide-field imaging with substantial computational...
The LOFAR Two-metre Sky Survey (LoTSS) Data Release 3 (DR3) now surpasses its predecessor, DR2, in both scope and source count—covering nearly 90% of the northern sky and revealing millions of new radio sources. Identifying optical and infrared counterparts to these sources is essential for determining their properties (e.g. redshift, morphology, luminosity) and enabling further scientific...
Sub-arcsecond imaging with the ILT has become more accessible over the last decade, thanks to efforts to build a publicly available pipeline using LOFAR-specific tools, which has resulted in a dramatic increase in the number of publications. The ILT's combination of resolution, field of view, and low observing frequency make it a unique instrument for a wide range of scientific applications,...
The LOw Frequency ARray (LOFAR) is one of the world's leading observatories at low radio frequencies. With its pan-European baselines reaching up to 2000 km in length, it is capable of achieving a sub-arcsecond angular resolution at frequencies below 200 MHz. However, the use of its international baselines has been hindered for most of the current lifetime of the observatory due to technical...
The rapid expansion of satellite mega-constellations, such as Starlink, presents new challenges to low-frequency radio astronomy. In this talk, I present results from NenuFAR observations revealing strong and highly polarized radio emissions from Starlink satellites below 100 MHz. I will discuss the observational signatures, potential origin of the radiation, implications for calibration and...
This research looks at the feasibility and technicalities of using the Low Frequency Array (LOFAR) as a method for detecting and tracking satellites and space debris. It will consider using LOFAR as the receiver in a passive bi-static solution with the French GRAVES space radar as emitter to observe and identify objects in Earth orbit.
Based on Lunar reflections of GRAVES' emissions...
While not a science talk, this presentation aims to provide an overview of the regulatory landscape and technical approach to protect LOFAR in an increasingly crowded radio spectrum. I will introduce the basics of spectrum management, including the international landscape that governs radio frequency use, and the role of CRAF in protecting radio astronomy. The talk will also explain how...
Observations of interplanetary scintillation (IPS) offer a way to provide global measurements of the inner heliosphere using ground-based systems. LOFAR offers capabilities in this area beyond those of other instruments, visualising the turbulence giving rise to IPS during the passage of a Coronal Mass Ejection and associated with the tail of a comet.
Since March 2025 the LOFAR-UK Rawlings...
Solar radio emissions originate from a wide range of phenomena — from faint gyrosynchrotron emission associated with CMEs, to thermal emission from the quiet Sun, to intense coherent emissions from solar radio bursts. These emissions can span up to nine orders of magnitude over small spans in time and frequency, requiring spectroscopic snapshot imaging to capture their full complexity....
Over the past 20 years, low-frequency solar radio astronomy has opened a new spectral window on the Sun. Distributed array telescopes, capable of fast interferometric imaging observations and electronic pointing have completely changed the technical and scientific approaches to studying various aspects of solar and heliospheric activity at frequencies between 20 and 300 MHz. Among them, LOFAR...
For the long-wave radio spectrum in which LOFAR operates, the ionosphere is of key importance in the context of radiation transfer and is a source of distortion in the recorded signal. Therefore, good knowledge and predictability related to the shape and dynamics of the ionosphere is extremely important for the LOFAR system [1].
However, for astrophysical research it is a disadvantage, it...
LOFAR (LOw Frequency ARray) radio telescope network enables high-resolution interferometric observations in the frequency range of 10 – 240 MHz. It can be used as a distributed array, but utilising a single LOFAR station can also provide valuable information. The cross-correlation data enable sky imaging at selected frequencies, with a time resolution of 1 second. Such mapping can be used for...
The Earth’s ionosphere originates propagation effects at various orders that can be observed on radio waves that traverse it. Ionospheric propagation effects can be utilized to infer properties of the ionosphere: for example, temporal fluctuations in the received radio-wave intensity (or scintillation) can be associated with irregularities forming in the inertial subrange of the spatial...
The Low Frequency Array (LOFAR) is one of the most advanced radio telescopes in the world. When radio waves from a distant astronomical source traverse the ionosphere, structures in this plasma affect the signal. The high temporal resolution available (~10 ms), the range of frequencies observed (10-90 MHz & 110-250 MHz) and the large number of receiving stations (currently 52 across Europe)...
LOFAR is the most sensitive and precise lightning interferometer currently operational. The LOFAR lightning research group has been using this capability to unveil lightning plasma physics that is impossible to explore in any other way. In particular, the lightning group has made significant progress in imaging and understanding lightning initiation, propagation, cloud-top discharges,...
How lightning starts is still an open question in the field of lightning physics. The in-situ electric fields observed within thunderstorms from decades of balloon measurements are far too low for both the breakdown of virgin air or what is known as the the streamer-to-leader transition. Past observations have implicated fast breakdown (FB) as a method by which lightning does initiate, however...
Observing the Sun in the radio domain is a powerful tool to detect and study the presence of shock waves in the solar corona, especially in the absence of other clear observations of coronal mass ejections (CMEs) capable of driving these shocks. Electrons accelerated by coronal shocks can be remotely detected through the radio waves that they emit in the form of type II solar radio bursts. In...
Detailed interferometric radio observations of solar activity allow us to constrain the dynamics of high-energy electron beams accelerated in flares and coronal mass ejections (CME), and thus to better model and study space weather effects. We report here a comparative analysis of two similar solar activity periods observed by LOFAR LBA on September 24 and 28, 2023. Both events exhibited the...
The UK’s NERC-funded Radio Investigations for Space Environment Research (RISER) project addresses the chain of events through which the Sun creates adverse space-weather conditions at Earth and within the Earth’s space environment. RISER aims to investigate how the LOw Frequency ARray (LOFAR) can be utilised for continuous and accurate tracking of inner-heliospheric and ionospheric plasma...
The Low-Frequency Array (LOFAR) has established itself as a formidable instrument in the field of solar physics and space weather, providing a unique vantage point for observing the Sun, heliosphere, and ionosphere. As we transition into the LOFAR 2.0 era, this presentation outlines the current status and future plans for leveraging LOFAR's capabilities, and the LOFAR IDOLS (Incremental...
In the solar system low frequency radio emission at frequencies ~200 MHz is produced by acceleration processes in the Sun and in planets’ magnetospheres. Such emission has been actively searched for in other stellar systems, as it would potentially enable the study of the interactions between stars and their exoplanets’ magnetospheres. Here we present a method meant to measure the flux density...
A key question in astronomy is whether there are habitable planets around other stars. Exoplanet habitability is largely determined by the stellar environment, with stellar eruptions buffeting exoplanets while the stellar wind slowly erodes the upper layers of the atmosphere. Traditional methods struggle to directly measure the stellar environment, in particular for low-mass stars. However,...
Gamma-ray binaries are unique laboratories for studying the interplay between relativistic outflows and dense stellar winds, producing variable non-thermal emission radio to very-high-energy (TeV) gamma rays. Resolving the spatial structure and evolution of the radio-emitting regions is essential for understanding the mechanisms driving particle acceleration and non-thermal emission in these...
Despite decades of effort, the detection of low-frequency radio emission from exoplanetary systems remains an open challenge. In this talk, we will present recent results from NenuFAR, including a tentative 6σ detection of a radio burst toward the well-studied hot Jupiter system HD 189733. The highly circularly polarized burst is consistent with coherent emission mechanisms such as the...
Gas-giant exoplanets are expected to generate low-frequency radio emission (< 40 MHz) via the cyclotron maser mechanism. Detecting this emission is likely the only viable way to measure exoplanets’ magnetic field and space-weather conditions. Despite many attempts, there has not been a confirmed detection of an exoplanet in the radio band. I will present results from our ongoing search for...
