Conveners
Session: ISM / magnetism / other
- Cathy Horellou
Session: CR / lightning / other
- There are no conveners in this block
Session: Surveys and Methods (1)
- Francesco de Gasperin (IRA INAF)
Session: Surveys and Methods (2)
- Virginia Cucciti
Session: Galaxy Clusters (1)
- Reinout van Weeren
Session: Galaxy Clusters (2), Planets (1)
- Andrea Botteon (INAF-IRA)
Session: Planets (2), Transients and Pulsars (1)
- Jason Hessels (ASTRON & University of Amsterdam)
Session: Transients and Pulsars (2)
- Antonia Rowlinson
Session: Sun and Space Weather (1)
- Pietro Zucca (ASTRON - Netherlands Institute for radio astronomy)
Session: Sun and Space Weather (2), Cosmology (1)
- Andrzej Krankowski
Session: Cosmology, EoR (2)
- Dominik Schwarz
Session: LOFAR ERIC Celebration
- There are no conveners in this block
Session: Galaxy Clusters (2), Other
- Emmy Escott (Durham University)
Session: AGN (1)
- Gabriella Di Gennaro (Hamburg Observatory)
Session: AGN (2)
- Olaf Wucknitz (Max-Planck-Institut für Radioastronomie)
Session: Closing
- Roberto Pizzo
The LOw-Frequency ARray (LOFAR) provides a unique opportunity to probe the magneto-ionised structure of our Galactic neighbourhood with great resolution. We will present a new mosaic created with the LoTSS-DR2 data, which shows polarised synchrotron emission in the high-latitude inner Galaxy. Faraday tomography of this data reveals a remarkably ordered structure whose orientation aligns well...
Radio continuum emission from galaxies at gigahertz frequencies can be used as an extinction-free tracer of star formation. However, at frequencies of a few hundred megahertz, there is evidence for low-frequency spectral flattening. We wish to better understand the origin of this low-frequency flattening and, to this end, perform a spatially resolved study of the nearby spiral galaxies M51 and...
Radio galaxy jets that undergo continuous precession trace an unique “S-shaped” pattern in the plane of the sky. Such galaxies hint at a more restless nature of the central AGN and studying them can help us gain rare cues about the dynamic interplay between radio jets, the central active region, and the intergalactic medium. Multifrequency radio studies of such jets can help understand their...
Peaked-spectrum sources, characterized by their distinctive peaked radio spectra, are likely progenitors of radio loud AGN and serves as an important tool to understand the formation and evolution of AGN. The new, high sensitivity Low Frequency Array (LOFAR) surveys make it possible to study these sources to a low frequency (< 100 MHz). In this work, for a sample of 1520 quasars, we use the...
We report the discovery of an AGN remnant in the galaxy group Abell 1318. After a thorough analysis of the host and environment, we conclude that the intriguing morphology is the result of the unsettled nature of the system and discuss the implications of these findings.
There are a great number of questions about lightning, and perhaps the most fundamental remains unanswered - how does lightning initiate. Lightning initiation can be a very weak, compact and fast process, and it has evaded detection by all instruments but one, the LOFAR radio telescope. In order to study initiation, we are exploring how our imager and its point spread function behave under...
Measuring radio signals from cosmic-ray air showers has enabled detailed air shower reconstructions and cosmic-ray mass composition analyses with LOFAR.
LOFAR is already a dense array for air-shower standards; with nearly 60,000 antennas in a 1 km diameter, the low-frequency part of SKA in Australia will increase this density by two orders of magnitude.
As we show from a detailed...
In the era of state-of-the-art radio observations the necessity of multi-wavelength and multi-frequency observations has been established as the only approach to understanding the radio source populations. This is demonstrated in all its glory via the panchromatic dataset of the COSMOS field, with the latest additions of the LOFAR and JWST datasets. Approaches as such enable us to image in...
We present the deepest sub-arcsecond wide-field image with LOFAR, obtained with 32 hours of international LOFAR data of the ELAIS-N1 deep-field. This image reveals structures of various astronomical objects with a resolution that surpasses the LOFAR Two-metre Sky Survey (LoTSS) (Shimwell et al. 2017, 2022) and the LoTSS-deep fields (Sabater et al. 2021; Kondapally 2021) by a factor 20. We...
We combine the power of blind integral field spectroscopy from the Hobby-Eberly Telescope (HET) Dark Energy Experiment (HETDEX) with sources detected by the Low Frequency Array (LOFAR) to construct the HETDEX-LOFAR Spectroscopic Redshift Catalog. Starting from the first data release of the LOFAR Two-metre Sky Survey (LoTSS), including a value-added catalog with photometric redshifts, we...
The Lofar Two-meter Sky Survey (LoTSS) had its second data release (DR2) published in 2022. It provides the largest radio sources catalogue to date, including 4.4 million sources and covering 5600 square degrees of the sky, and therefore an excellent opportunity for studies of the large-scale structure of the Universe. In this talk, I will present the results based on one-point correlation...
The wide bandwidth and high frequency and time resolution capabilities of LOFAR make it an excellent instrument for observing both large and small scale ionospheric plasma structures. The geographical distribution of LOFAR stations further permits characterisation of these structures as they propagate through the mid-latitudes. LOFAR was used to track the propagation of a travelling...
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 in LBA and even attempt <30 MHz imaging and long-baseline...
The WEAVE-LOFAR (WL) survey will provide the LOFAR community with more than 1 million optical spectra (365-960nm with R=5000) of low-frequency radio sources in the coming 5 years. This survey will not only provide spectroscopic redshifts and reliable source classification, but will also enable detailed studies including the role of accretion and AGN-driven feedback, the star formation history...
The LOFAR Two-metre Sky Survey is an ongoing deep low frequency survey of the entire northern sky. In 2022 we released LoTSS-DR2 which consisted of images and data products covering about 1/4 of the northern sky. Since then we have gathered a vast amount more data and by mid 2024 LoTSS observations will be over 85% complete with 15,000hrs and 20PB of data recorded. In this talk I shall provide...
Virgo, the closest galaxy cluster to us, is a unique laboratory to probe the interactions of star-forming and radio galaxies with the intracluster medium. These processes include the compression and the ram pressure stripping of the interstellar medium of star-forming galaxies and the AGN-mediated feedback of radio galaxies.
Radio frequency observations are a critical tool to understand...
Data reduction pipelines are the cornerstone of scientific output. Catching mistakes as early as possible is paramount for more complex pipelines to succeed. Over the past decade our understanding of the LOFAR instrument and data reduction workflows has grown substantially and now encompasses at least three major pipelines, each tackling more complex or harder problems. In this talk I will...
LoTSS DR2 is currently the largest radio catalogue in existence, but matching radio with optical sources, essential for science, has presented some huge challenges. I'll describe the steps we've taken to achieve our present 85% optical ID rate (by far the largest set of optical IDs for any radio catalogue) and the science that enables, looking particularly at the very large samples of AGN that...
In this talk, I will present the first homogeneous X-ray and radio study of galaxy clusters using LOFAR and CHEX-MATE XMM observations.
Past studies have shown the presence of radio-X-ray connections in galaxy clusters and used them to derive constraints on cluster energetics and particle (re-)acceleration. However, many aspects of these processes are yet to be understood. With the advent of...
Galaxy clusters can host significant quantities of diffuse radio emission. The origin of this radio emission is still poorly understood. However, low frequency radio observations can help to shine light on the acceleration mechanisms that produce such diffuse emission. In particular, galaxy cluster mergers can re-accelerate seed electrons to extreme energies. Radio observations below 30 MHz...
Low surface brightness galaxies are not that different from known and
well-studied brighter galaxies — they are also a mixture of stars,
gas, and dust (even though only recently we have found IR counterparts for those unfamiliar objects), and they undergo similar processes, such as dust attenuation and emission, which are essential to explain their physical properties. Those faint sources...
Luminous and ultraluminous infrared galaxies (U)LIRGs offer unique laboratories to understand various physical processes which drive the evolution of galaxies across cosmic time.(U)LIRGs are the most extreme star-forming galaxies in the local Universe, and they are primarily triggered by interacting and mergers of gas-rich galaxies. As such, they provide excellent local laboratories to study...
As we know, the ionosphere is of key importance in the context of long-wave radiation transfer from outer regions to ground. Therefore, good knowledge and predictability related to the shape and dynamics of the ionosphere is extremely important for the LOFAR system [1] to exclude the influence of this closest obstacle in the observational data of astrophysical objects.
On the other hand, good...
In 2020, a project for building a Bulgarian LOFAR station (LOFAR-BG) was approved and included in the Roadmap for Research Infrastructure of the Republic of Bulgaria. The same year started a H2020 Widening project aimed at transferring knowledge in scientific research and the operation of a LOFAR station, in which partners were ASTRON (NL) and DIAS (IE). Here we present the progress to date...
In galaxy clusters, we have observed that star-forming spiral galaxies can evolve into passive S0 galaxies. This process, known as 'environmental processing', is primarily driven by the ram pressure exerted by the intracluster medium (ICM) on the galaxies that enter the cluster. This pressure can strip a galaxy of its interstellar medium (ISM), which can stop its star formation. Recent...
Diffuse radio emission has been observed in plenty of galaxy clusters and classified in radio halos, relics or revived fossil plasma depending on its morphological and spectral properties. A category that is still less widely studied is that of radio phoenices. These sources are thought to trace fossil lobes of radio galaxies that have been re-energised by adiabatic compression after the...
Observations with LOFAR and other radio telescopes have revealed a plethora of filamentary structures in the sky. From the centre of the Milky Way out to radio galaxies, radio relics and other structures. These synchrotron filaments yield important information about the underlying magnetohydrodynamical turbulence, e.g. the intermittency of magnetic fields. At some scale these fields are...
In this talk, I will discuss a new radio transient that we found in a commensal transient search of the LOFAR survey data (de Ruiter et al. 2023, submitted). The source has shown several bright minute-duration radio flares with a periodicity of two hours. Long-period radio transients are an emerging class of extreme astrophysical events of which currently only three are known (Caleb et al....
Stellar winds govern the lives of stellar systems, from dictating the evolution of the star itself to eroding the atmospheres of exoplanets. The impact of the wind on a stellar system is largely determined by the mass-loss rate -- which is notoriously difficult to measure on dwarf stars since the wind is so tenuous. Currently, mass-loss rates of cool stars have to be modelled or inferred...
Gaseous exoplanets generate low-frequency radio emission (<40 MHz), which is associated with aurorae via circularly polarized cyclotron maser mechanism and is directly related to the surrounding space weather. To obtain a detailed analysis of this mechanism, one must measure the stellar wind's electron density and the planet's magnetic field, which is only possible with observations at radio...
The LOFAR International Telescope serves as an exceptionally powerful instrument for conducting thorough surveys of the sky at extremely low frequencies. Despite the extensive research on the evolution of Active Galactic Nuclei (AGNs), many aspects of this process remain elusive. Existing evolutionary models, derived from numerous observations, suggest that Gigahertz Peak Spectrum (GPS) and...
In the last two decades, an increasing number of studies of galaxy clusters and groups have demonstrated the importance of the interplay between the Intra-Cluster Medium (ICM) and Active Galactic Nuclei (AGN) for the overall evolution of the largest-scale structures. However, only in recent years, thanks to new-generation instruments such as LOFAR, we were able to move these investigations to...
NGC7618/UGC12491 is a major group merger in the Local Universe that has been intensively studied in the X-rays, showing a series of complex features involving both groups. Only recently, thanks to the continuous improvement in capabilities of the instrumentation, the possibility to complement the work with the study of non-thermal phenomena in the radio regime has been available.
In this...
Radio relics are one kind of diffuse synchrotron emission that can be observed in merging galaxy cluster's outskirts, believed to trace particle (re-)acceleration by ICM shock waves. They show elongated shapes in the $\sim$Mpc scales and brightness distributions peaking at the shock location, decreasing toward cluster center. Two relics can be generated by a single merger event and be observed...
Pulsar Timing Arrays (PTAs) exploit the extreme rotational stability of pulsars to chase the direct detection of nanoHertz-frequency gravitational waves (GWs), hence expanding the accessible windows of the GW spectrum.
In 2023, the European together with the Indian PTA (EPTA, InPTA), the North American PTA and the Australian PTA presented three series of articles reporting the first...
The Crab Nebula, the pulsar wind nebula surrounding the Crab pulsar, is one of the most thoroughly studied objects in the sky, and it might appear unlikely that, at this stage, radio observations could shed new light on its properties. In this talk, I will present a subarcsecond resolution image of the nebula at 150 MHz, possibly the highest dynamic range image ever made with LOFAR. The new...
The last decade has revealed that the Universe creates fast radio transients that are visible across giga-parsec distances and a vast range of timescales, lasting from tens of seconds to as short as nanoseconds. These ephemeral radio flashes occur sporadically and they must originate from coherent radiation processes in environments with extreme energy density. We aim to understand the...
Understanding electron acceleration associated with magnetic energy release across short timescales is a major challenge in solar physics. Using subsecond and narrow-bandwidth ($\Delta{f}/f\sim10^{-3}-10^{-2}$) solar radio bursts fine structures, we present a statistical analysis of frequency- and time-resolved imaging of individual radio spikes and type IIIb striae associated with a coronal...
We present LOFAR observations of an M class flare, that was accompanied by intense type III radio bursts. Some isolated burst have a fundamental-harmonic structure, but for most bursts this is not visible due to a rapid succession of bursts. Spectroscopic imaging with LOFAR shows type III bursts as a compact source for a given observing frequency. The intensity varies with burst evolution, but...
Radio waves that travel though the ionosphere experience a deformation in their wavefronts. Those perturbation are
caused by inhomogeneities in the spatial distribution of the refractive index. The received signal is affected by temporal
fluctuations in its phase and intensity.
Ionospheric disturbances are present in received signal with frequencies between the VHF and C band. In...
LOw-Frequency ARray (LOFAR) consists of a European array of 52 radio telescopes designed for use, either collectively as an international interferometer or independently as separate stations. There are three LOFAR stations, localised in Poland, one of which is under the ownership of the Space Research Centre of the Polish Academy of Sciences. Positioned in Borówiec, Poland, the PL610 LOFAR...
Quasi-periodic scintillations (QPS) are recurrent radio scintillation features generated by plasma structures in the Earth’s ionosphere. They are generally categorised into two forms, symmetric and asymmetric. Symmetric QPS are characterised by a series of signal intensity fringes either side of a distinct signal fade. In previous literature, such features have only been observed using single...
Over the past 10 years, increasingly intensive studies of the ionosphere have been carried out using LOFAR data [1-5]. LOFAR detects scattering of high frequency (HF) (MHz) electromagnetic waves (EMW) emitted by astrophysical sources (supernovae, pulsars) on ionospheric (wave) excitations/plasma structures. Excitation and penetration of increasingly intense nonlinear active plasma structures,...
The Low-Frequency Array (LOFAR) has established itself as a formidable instrument in the realm of solar physics and space weather, providing a unique vantage point for observing the Sun, heliosphere, and ionosphere. As we transition into the LOFAR2.0 era, this abstract outlines the current status and future plans for leveraging LOFAR's capabilities, and the LOFAR IDOLS (Incremental Development...
Following the cosmological principle, the observed dipole anisotropy of the cosmic microwave background (CMB), which is presumably due to the motion of the solar system, should also be detectable in the distribution of visible matter. This study uses a new Bayesian estimator to measure the cosmic radio dipole in several wide-field radio surveys, including the NVSS, VLASS and RACS-low...
Studying the redshifted 21-cm signal emitted by neutral hydrogen during the Epoch of Reionization and Cosmic Dawn is crucial for understanding the physics of the early universe. One of the challenges that 21-cm experiments such as LOFAR face is the contamination by bright foreground sources, which necessitate accurate spatial and spectral models to minimize the residual contamination after...
The advancement of 21-cm Cosmology, particularly in probing the Epoch of Reionization (EoR) and beyond (z>6), relies on deep, wide-field observations at low frequencies. At the low frequencies required for the EoR science-case, the inherent instability of an interferometer requires extremely precise direction-dependent calibration. Many tools for direction-dependent calibration utilize a sky...
Between December 2023 and April 2024 we conducted a VLBI experiment with LOFAR, NenuFAR, KAIRA and several stations of the LWA to try transatlantic interferometry in the LOFAR low band. Targets were Jupiter (at times of expected decametric bursts) and three bright pulsars. First goal is detecting fringes at all, which was not possible in a smaller experiment more than ten years ago. In the...
Radiation unintentionally emitted by electronics onboard of satellites in low Earth orbit has recently been detected with LOFAR at frequencies between 110 and 188 MHz. The detection of this unintended electromagnetic radiation, and the absence of its regulation, will have consequences for radio astronomy. In this talk I will present the latest observational results of this radiation, and...
Radio jets are present in a diverse sample of AGN, however, the mechanisms of jet powering are not fully understood. We use the complete, spectroscopic GAMA09 survey to measure the fraction of galaxies hosting radio and X-ray AGN, defined using LOFAR and eROSITA data, as functions of mass-scaled power indicators. We recover the previously found mass-invariant triggering and fueling mechanisms...
We utilize a combination of radio continuum observations and optical integral field spectroscopic (IFS) data to explore the impact of radio AGNs on the evolution of their host galaxies at both global and sub-galactic scales. We construct a comprehensive radio-IFS sample comprising 5578 galaxies at redshift $z<0.15$ by cross-matching the LoTSS) with the MaNGA. We revisit the tight linear radio...
Studies show that both radio jets from the active galactic nuclei (AGN) and the star formation (SF) activity in quasar host galaxies contribute to the quasar radio emission, yet their relative contributions across the population remain unclear. Here, I will present new constraints on the SF and AGN contribution to the quasar radio emission and their evolution with various physical processes,...
The X-ray emission from resolved knots in the jets of many blazar cannot be explained as a simple extension of the radio synchrotron spectrum. So far no general consensus could be reached on the relative importance of the different broadband-emission mechanisms at play. In particular, observing the low radio frequencies provide valuable constraints to test different emission models like...
The International LOFAR Telescope (ILT) represents a unique infrastructure, providing sub-arcsecond resolution at 150 MHz. Such capabilities will be unmatched even in the SKA era, and this makes the ILT desirable for a wide range of scientific cases: however, the full exploitation of this facility brings along many technical challenges, especially related to the data volume and calibration...
One of the most common explanations for the existence of megaparsec-scaled radio galaxies (also called giant radio galaxies or GRGs) is that they are older sources. However, this hypothesis has not been thoroughly tested on a statistically large sample, —attributable primarily to the demand for multifrequency data that spans a broad spectrum from low to high frequencies, matched in sensitivity...
The Low Frequency Array (LOFAR) is currently the only instrument capable of deep, high-resolution imaging at frequencies below 100 MHz. Sources selected from the 3C catalogue are some of the best studied powerful radio galaxies, with the largest number of available sensitive and high (kpc-scale) resolution images at GHz frequencies, (still) driving our current understanding of their dynamics...
Understanding the morphological evolution of radio-loud quasars (RLQs) across cosmic time offers unique insights into the physical conditions of the early Universe, the interaction of these RLQs with their surrounding medium, and the underlying mechanisms driving galaxy formation and evolution. Previous works, e.g., Barthel & Miley (1988, Nature), have laid the foundational understanding of...
We study the co-evolution between host galaxies and their central supermassive black hole (SMBH) with an unprecedented large sample of SDSS type-1 quasars which are also detected by the far-infrared (FIR) SPIRE instrument on Herschel. This subset of optical quasars gives us a unique opportunity to study systems for which both star-formation activity and active galactic nucleus (AGN) activity...
The nearby Coma galaxy cluster is a milestone for exploring magnetic fields and particle acceleration processes in the intra-cluster medium (ICM). Recent LOFAR observations at 144 MHz have revealed new features in the extended radio emission of this cluster: a bridge connecting the halo to the cluster, a sharp radio front at the halo's edge, and a compelling "accretion relic" situated beyond...
Diffuse radio emission in galaxy clusters is the best evidence for the presence of accelerated particles and magnetic fields on large scales. Current low-frequency surveys, such as LoTSS, are revealing a large number of spectacular radio sources, but detailed analysis on the radio properties is limited to the low-redshift and high-mass regime. At high redshift, the relatively short ages of the...
Radio observations of the tau Bootis system performed in 2017 using LOFAR have shown a tentative signal, which was interpreted as the potentially first detection of planetary radio emission [Turner et al. 2021]. The signal was weak, with a significance of ~3 sigma. Also, a single detection is not sufficient to clearly attribute the emission to the planet rather than the host star or its binary...
Sloshing motions in relaxed galaxy clusters are believed to play an important role in re-accelerating relativistic particles in radio mini-halos. As shown by recent studies, these motions of the thermal gas can also led to the redistribution of the non-thermal material ejected by the cluster central AGN on broader scale.
In my talk, I will report the results from a recently published study on...
Giant Radio Galaxies (GRGs) with a projected linear extent $>$0.7 Mpc were first found in 1974 and over 10,000 are now known. I present results based on my compilation of GRGs (a) from literature, and my visual inspection of (b) large-scale radio surveys in general (e.g. NVSS, SUMSS, RACS, LoTSS DR2, etc.) with $\sim$9,800 GRGs, and of specific regions like (c) the LoTSS Deep Fields (247...
We present performed in the 20–40 MHz range spectral and imaging LOFAR (LOw-Frequency ARray) observations of solar radio bursts fine structures, such as flag-like, sail-like, and dot-like that appeared on 8 April 2019. These structures were associated with type III solar radio bursts that occurred in the 40–80 MHz band. The mean duration and spectral widths of the fine structures range from...
Current radio interferometers output multi-petabyte-scale amounts of data per year making the storage, transfer and processing of this data a sizeable challenge. This challenge is expected to persist with the next-generation telescopes such as the Square Kilometre array (SKA) which will be considerably larger in size than current instruments. Lossy compression of interferometric data...
Galaxy cluster mergers are the most energetic events dissipating a significant portion of the energy in the ICM through shocks. There is clear evidence that radio relics are related to large cluster merger shocks, however the electron acceleration mechanism is not well understood, in particular, whether mildly relativistic electrons exist in the intracluster medium (ICM) and if they are...
Radio relics play a pivotal role in unravelling the intricate dynamics of galaxy cluster mergers, serving as key indicators of shock waves and particle acceleration processes. While extensively studied in the radio band, the investigation of radio relics at ultra-low frequencies (<100 MHz) remains limited due to technical challenges, such as ionospheric disturbances and high sky temperature...
Radio relics are extended diffuse sources that are thought to originate from shock fronts caused by galaxy cluster mergers and are found at the periphery of many dynamically disturbed clusters. However, the particle acceleration mechanism at the shock fronts and the formation of the relics is not yet well understood. A spectacular, large-scale extended radio relic has been found in the galaxy...
The LOFAR Two-meter Sky Survey is the largest extragalactic survey to date. As part of the final stages of our third generation interferometric data reduction pipeline, we have synthetized ~480.000 dynamic spectra in full polarisation in the direction of about 85.000 nearby stellar objects (including exoplanetary systems). I propose to present the main results from a preliminary statistical...
Since the early Universe, dark matter has come together under the effects of gravity to form massive haloes, within which galaxies form. This distribution of matter is not uniform and instead we see galaxies distributed in a web throughout the Universe - the large-scale structure. Alongside a number of factors (e.g mergers and feedback processes), these large scale environments are likely to...
