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LOFAR Family Meeting 2024
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Zuid 1 (Pesthuis Leiden)
Zuid 1
Pesthuis Leiden
Pesthuislaan 7
2333 BA Leiden
Description
LOFAR Family Meeting 2024
The LOFAR Family meeting 2024 is hosted by Leiden Observatory, the astronomical institute of Leiden University, in the Netherlands. Established in 1633 to house the quadrant of Rudolph Snellius, it is the oldest operating university observatory in the world.
Venue
The conference will take place in the Pesthuis which was built in the 17th century as a place to quarantine and treat sufferers of the plague, but it was never actually used for that purpose. These days it serves as a convention center.
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11:00
Registration / lunch
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Welcome
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1
WelcomeSpeakers: Jessica Dempsey, Wim van Cappellen
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2
LOFAR 2.0: running the new observatorySpeakers: Jessica Dempsey, Wim van Cappellen
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3
LOFAR 2.0: science overviewSpeaker: Jason Hessels (ASTRON & University of Amsterdam)
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4
SDC operations: achievement, past & future challengesSpeaker: Roberto Pizzo
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5
LOFAR2.0 development status and plansSpeaker: Boudwijn Hut
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6
SDC Developments towards LOFAR 2.0Speaker: John Swinbank
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1
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15:15
coffee / tea
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LOFAR 2.0 Commissioning plan
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7
LOFAR 2.0 commissioning areas: status, challenges, plansSpeaker: Michiel Brentjens (ASTRON)
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11
Discussion: LOFAR2.0 pipelines roadmap
Discussion: LOFAR2.0 pipelines roadmap with contributions from:
Andre’ Offringa, RAPTHOR pipelines
Francesco de Ghaperin, LBA pipelines
Leah Morabito, VLBI pipelinesSpeaker: Timothy Shimwell et al. (ASTRON)
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7
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11:00
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Session: ISM / magnetism / otherConvener: Cathy Horellou
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12
First detections of Carbon Radio Recombination Lines with the NenuFAR telescope
In this talk, I will present the work we have been carried out over the past month with the data from the NenuFAR Long-Term 10 program. This program has been aimed at observing radio recombination lines between 10 and 85 MHz in absorption in various Galactic lines of sight with the newly commissionned NenuFAR telescope in Nancay. In this talk, I will present the first lines of sight for which we have reduced the data into a scientifically exploitable format: Cassiopeia A, Cygnus A, and Taurus A. For these sources, we used the beamforming mode, and we integrated several tens of hours on each source. The nominal spectral resolution was 95.4~Hz. We built and applied a reduction pipeline, mostly to remove RFI contamination and correct the baselines. We also performed a rudimentary fitting of the spectral lines observed in absorption, associated to line-of-sight clouds. Cas A is the brightest background source and represents an appropriate laboratory to benchmark this new telescope. On this source, we detected 398 lines, with improved signal-to-noise ratio (SNR) and spectral resolution compared to the most recent detections by LOFAR. Cyg A is also a bright source, however, we stacked lines by groups of a few tens of lines to improve the quality of our fitting process. Again, we reached much better SNR and spectral resolution than the most recent detections by LOFAR. Finally, we also detected CRRLs towards Tau A for the first time. The variation of spectral linewidths with the electronic quantum number provides constraints on the physical properties of the clouds: Te, ne, as well as the temperature of the radiation field T0, the mean turbulent velocity and the typical size of the cloud. Globally, our final constraints slightly differ from those inferred from LOFAR results, which could be related to the large beamsize of NenuFAR.
Speaker: Lucie Cros -
13
Revealing the Local Bubble and the Complex of Local Interstellar Clouds in the LoTSS-DR2 Faraday tomographic data
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 with the HI filaments and the magnetic field. We estimate the minimum distance to the Faraday structures to be between 40 and 80 pc, which puts them near the Local Bubble wall. The emission is organised in a large gradient in Faraday depth whose origin we associate with the curved wall of the Local Bubble. Comparing our data with a model of the Local Bubble wall, we conclude that we might be probing a contribution of the
medium inside the Local Bubble cavity as well, corresponding to the complex of local interstellar clouds (LICs).Speaker: Vibor Jelic (Ruder Boskovic Institute) -
14
ApPolLo - Apertif counterparts of polarised LOFAR sources
Polarisation studies over a significant redshift range are an important tool in understanding the evolution of cosmic magnetic fields and unrevealing their origin. As most depolarisation effects are highly wavelength depended, 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 show significant polarised emission at 144\,MHz, we image their 1.4\,GHz counterparts and construct a catalogue of 598 polarised sources.
We present preliminary results of the comparison of polarisation properties and Rotation Measure values at 1.4\,GHz and 144\,MHz, including the first redshift-dependent estimate of the Rotation Measure dispersion in cosmic web filaments.
Speaker: Anna Berger -
15
The ultra-low frequency radio continuum spectra of nearby galaxies
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 M101. This is an important use case for LOFAR LBA observations.
For the analysis of M51, we used radio continuum intensity maps between 54 and 8350 MHz at eight different frequencies. We found that cosmic-ray ionisation losses play an important role in the low-frequency spectral flattening alongside free-free absorption. We are working on a similar analysis in M101, using five radio maps between 54 and 4850 MHz. We would like to verify the importance of ionisation losses and focus on separate giant HII regions which can be resolved in M101.Speaker: Lovorka Gajović (Universität Hamburg, Hamburger Sternwarte) -
16
Studying radio galaxies with twisted jets using multifrequency data
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 morphological evolution and can reveal the underlying cause of the jet precession. When complemented with multiwavelegth data, such galaxies can help towards deeper understanding of SMBH-galaxy co-evolution. In this talk, I will present multifrequency radio analysis of an S-shaped quasar with precessing jets and discuss its evolution.
Speaker: Arpita Misra (Jagiellonian University) -
17
Extend the extragalactic peaked-spectrum sources to 54 megahertz
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 LOFAR Low Band Array (LBA) 54 MHz, High Band Array (HBA) 144 MHz, and the Very Large Array (VLA) FIRST 1.4 GHz data to measure the spectral index: $\alpha^{144}_{54}$ and $\alpha^{1400}_{144}$. For all samples, there is no significant evolution of the spectral index with the redshift. Compared to compact sources, the extended sources have a steeper spectral index. We also use these parameters to find megahertz peaked sources. We find that the fraction of megahertz peaked spectrum sources is almost constant with the evolution of redshift, bolometric luminosity, and supermassive black hole (SMBH) mass, which points out that the fraction of MPS sources does not undergo significant changes in relation to the host galaxies' properties.
Speaker: Sai Zhai (Leiden University) -
18
Old AGN remnant sculpted by IGM sloshing
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.
Speaker: Aleksandar Shulevski -
19
Near-Field Interferometry of Lightning with LOFAR
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 these low SNR conditions. We are using a unique beamforming algorithm that utilizes near-field imaging, called TRI-D (Time Resolved Interferometric 3-Dimensional imager). Antennas on all sides of the lightning flash are measuring different polarizations, yielding a 3-dimensional location and polarization information of every radio source. In this work, we perform a Monte Carlo error analysis which simulates the voltages on each antenna from an assumed dipole emitter, adds normally distributed noise, and then reconstructs the source properties with TRI-D. The difference between the simulated input and the reconstruction gives us an estimate of the resulting error bars. We will show a detailed account of the interferometry technique that produces our data, the Monte Carlo simulation that tests the accuracy of our model and finally, our polarization results.
Speaker: Paulina Turekova (ASTRON)
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12
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10:30
coffee / tea / posters
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Session: CR / lightning / other
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21
Measuring high-energy cosmic rays at SKA-Low
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 simulation study, this allows to reconstruct the longitudinal evolution of the number of particles in the shower, rather than just its maximum. This level of detail for individual showers has not yet been possible in cosmic-ray observatories.
We discuss the new possibilities for cosmic-ray measurements, which include additional independent information on the mass composition between $10^{16}$ and $10^{18}$ eV, in particular the proton fraction, which is astrophysically relevant yet difficult to distinguish from helium. Moreover, the main hadronic interaction models predict observably different longitudinal profiles. Hence, measuring these would be helpful in constraining hadronic physics beyond energy levels in man-made accelerators.Speaker: Arthur Corstanje (Vrije Universiteit Brussel) -
22
The Initiation of Lightning Dart Leaders with LOFAR
During a lightning flash there are a multitude of propagating plasma channels, called leaders, that grow through the thunderstorm. After their growth these channels cool and lose ionization and conductivity. After hundreds of milliseconds these channels exhibit current pulses that then propagate along the leader plasma channels and re-heat them. These pulses are called dart leaders due to their fast propagation speed (~10^7 m/s). The physics of these dart leaders, how they get started and how they propagate, is not understood. In this work we image the beginnings of lightning dart leaders with the LOFAR radio telescope in order to try and understand how they start. We have found that each dart leader is unique, which makes for an interesting challenge to find the underlying physics. Some dart leaders are preceded by other small discharges of different types, while others seem to start out of the blue. Some dart leaders exhibit an exponential rise in radio intensity at their beginning, and others do not. After initiating, every dart leader shows strong fluctuations in radio intensity that could be due to poisson fluctuations in radio emitters, longer time-scale fluctuations in the plasma physics (i.e. pulsing), or perhaps even due to structure in the underlying lightning channel. It is a challenge to separate these three mechanisms. In this talk we will present LOFAR images of lightning dart leaders, with explanations of what we see, and possible explanations of our data.
Speaker: Brian Hare (ASTRON) -
23
LOFAR cross correlation with eBOSS
We cross-correlate the LOw-Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) second data release (DR2) catalogue with the extended Baryon Oscillation Spectroscopic Survey (eBOSS) luminous red galaxies (LRGs) sample to extract the Baryon Acoustic Oscillation (BAO) signal and constrain the bias of radio sources in LoTSS DR2.
In the LoTSS catalogue, employing a flux limit of $1.5$mJy and a signal-to-noise ratio (SNR) of $7.5$, and considering a redshift interval of $\Delta z=0.06$ in the eBOSS LRG catalogue, we measure both the cross angular power spectrum $C_{\ell,x}$ and the eBOSS auto-power spectrum $C_{\ell,e}$. These measurements are performed across various eBOSS redshift slices. By marginalising over the broadband information of the $C_\ell$'s, we detect a mild BAO signal, and determine the bias of radio sources.Speaker: Jinglan Zheng
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12:15
Group picture
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12:25
Lunch (external)
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Session: Surveys and Methods (1)Convener: Francesco de Gasperin (IRA INAF)
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24
Low-frequency VLBI with the International LOFAR Telescope
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 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 and logistical challenges: its phased-array design, the ionosphere, lack of known suitable calibrator sources, and lacking software tools. For this reason, many projects have relied only on the Dutch part of the array, using baselines up to 120 km. Thanks to the Long Baseline Working Group, a strategy has been developed to enable the calibration of the international stations. This has unlocked the highest resolutions (~0.3 arcseconds) attainable with LOFAR, enabling a wide variety of research for the first time. In this talk, I will present the details of the calibration strategy, recent scientific results, the current development status of the pipeline, and a future outlook for what to expect from the International LOFAR Telescope in the near future.
Speaker: Roland Timmerman -
25
The high-resolution COSMOS: peering into the unknown with LOFAR and JWST observations
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 high resolution and sensitivity the active galactic nuclei (AGN) radio population and extract information about the radio properties and their interaction with the environment. We will present the first high-resolution wide-field map of a Dec+02 field using HBA LOFAR observations and the latest LOFAR VLBI pipelines to obtain an angular resolution of 0.8” across 1 sq. deg. We will discuss the challenges related to processing low Declination, high-sensitivity observations, and we will share with the community the steps taken to overcome these, which will benefit also the preparations for LOFAR2.0 observations. We will also present the 6” resolution 144 MHz map, and will discuss how the LOFAR observations of COSMOS, in combination to multi-frequency (from 144MHz to 3 GHz) and multi-wavelength (X-ray to radio) data from the panchromatic dataset of COSMOS, help us understand the nature of the radio source populations and their interrelation to their hosts and large-scale environment (e.g. galaxy groups, density fields, and cosmic web). I will lastly present our efforts to study the physical properties and hosts of radio AGN using LOFAR and JWST sub-arcsec observations.
Speaker: Dr Eleni Vardoulaki (National Observatory of Athens IAASARS/NOA) -
26
Into the Depths: Unveiling ELAIS-N1 with LOFAR's deepest sub-arcsecond wide-field images
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 obtain a best sensitivity of 14 μJy/beam with about 16 times less total observing time than what would be required for the same depth using solely the Dutch high-band antennas from LOFAR (Shimwell et al. in prep).
LoTSS already provides us with wide-field images of almost the complete northern sky at 144 MHz and 6” resolutions, revealing up to 5 million objects (Shimwell et al. 2022). However, 90% of the radio sources at 6” remain unresolved at these frequencies, prompting the need for higher resolutions. To address this, we have built upon the work from Morabito et al. (2022) and Sweijen et al. (2022), by improving the workflow for wide-field imaging incorporating international LOFAR data. Our focus was in particular on refining the DI calibration and automating the selection and calibration of direction-dependent calibrators. This effort resulted in three wide-field images at 0.3”, 0.6”, and 1.2” resolutions, which enables comparisons of source detections across resolution and sensitivity.
Beyond the extensive scientific output that can be derived from our deep sub-arcsecond wide-field image of ELAIS-N1, will our efforts also advance us toward the development of a robust and fully automated LOFAR VLBI pipeline. This pipeline is essential for efficiently processing upcoming sub-arcsecond northern sky surveys, facilitating the study of the low-frequency universe at the smallest angular scales.
Speaker: Mr Jurjen de Jong (Leiden Observatory) -
27
HETDEX-LOFAR Spectroscopic Redshift Catalog
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 extracted 28,705 HETDEX spectra. Using an automatic classifying algorithm, we assigned a star, galaxy, or quasar label along with a velocity/redshift. We supplemented these classifications with the continuum and emission line catalogs of the internal, fourth data release from HETDEX (HDR4). We measured 9,087 new redshifts; in combination with the value-added catalog, our final spectroscopic redshift sample is 9,710 sources. This new catalog of distances facilitates research to determine the [O II] emission properties of radio galaxies from 0.0 < z < 0.5 and the Lyman-alpha emission characteristics of both radio galaxies and quasars from 1.9 < z < 3.5. Additionally, by combining the unique properties of LOFAR and HETDEX, we will be able to measure star formation rate (SFR), stellar mass, and reddening properties. Using the Visible Integral-field Repicable Unit Spectrograph (VIRUS), we can measure the emission lines of [O III], Hβ, [Ne III], and [O II] and evaluate line-ratio diagnostics to determine whether the emission from these galaxies is dominated by AGN or star formation.
Speaker: Maya Debski (University of Texas at Austin) -
28
Cosmology from LOFAR Two-metre Sky Survey Data Release 2: Counts-in-Cells statistics
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 function. This statistic, also known as counts-in-cells, offers insights into the spatial distribution of radio sources. I will show that the distribution of the radio sources is non-Poisson which is likely due to multiple physical components of individual sources. Employing Cox process, I utilize both compound Poisson and negative binomial distributions to model the distribution of the sources. Through statistical tests in both frequentist and Bayesian frameworks, I evaluate which distribution fit better to the observed source distribution.
In the second part of the talk, I will use statistical measures from counts-in-cells to calculate the two-point correlation function. It's widely known that the variance of counts-in-cells is directly linked to the angular two-point correlation function. By analyzing the variance of counts-in-cells in various cell sizes within the Healpix pixelization scheme, I will fit it to a single power-law model representing the angular two-point correlation function. This helps us determine the amplitude and exponent of the power-law by a computationally very cheaper method.
Speaker: Morteza Pashapour-Ahmadabadi (University Bielefeld) -
29
Tracking travelling ionospheric disturbances in the mid-latitude ionosphere from Poland to the North Sea with LOFAR.
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 ionospheric disturbance (TID) containing embedded sub-structures which generated unusual scintillation patterns over a distance of >1200 km across Northern Europe. Broadband trans-ionospheric radio scintillation observations of these phenomena are, to our knowledge, unreported in the literature as is the ability to track them over such a distance. The features are characterised by an initial broadband signal fade and enhancement which is then followed by a series of interference fringes, caused by diffractive fringing as the radio signal transitions through regions of relatively steep plasma density gradient at the trailing edge of the plasma structures. The structures retained their characteristics consistently over the full 1200 km from Poland to the North Sea implying self-coherence for several hours. The TID propagation altitude of 110 km was directly measured from medium frequency radar demonstrating that these were E-region phenomena. Co-temporal GPS data was used to establish that these plasma density variations were very small, with a maximum likely amplitude of <<1% of ionospheric plasma density in the LOFAR field-of-view.
Speaker: Gareth Dorrian (University of Birmingham) -
30
Radial variation of anisotropic density turbulence from the low corona to 1au and solar radio observations
Radio signals propagating via solar corona and solar wind are significantly affected by density fluctuations, impacting solar radio burst properties as well as the observations of sources viewed through the turbulent atmosphere. Using large-scale simulations of radio-wave transport, the radial profile of anisotropic density turbulence from the low corona to 1 au is explored. For the first time, a profile of Heliospheric density fluctuations is deduced that accounts for the properties of extra-solar radio sources, solar radio bursts, and in-situ density fluctuation measurements in the solar wind at 1 au. Combining the anisotropic turbulence model with the space-craft frequency broadening measurements radial and perpendicular to radial velocities are deduced. The deduced properties of turbulence could be used to estimate the energy deposition rates due to Landau damping ion-sound waves and specific energy rate Alfven wave turbulent cascade at large scales.
Speaker: Eduard Kontar
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24
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15:30
coffee / tea / posters
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Session: Surveys and Methods (2)Convener: Virginia Cucciti
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31
Ultra-low frequencies with LOFAR: status and plans
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 imaging.
In this talk, I will recap the latest results obtained with the LBA system in interferometric mode, as an example I will show the most recent results on imaging Virgo A (M87) at 50 (and 150 MHz) using international stations. I will make an overview on the upgrades made to the Pipeline for LOFAR LBA (PiLL) and I will give a status update on the LOFAR LBA Sky Survey (LoLSS), that aims to cover the sky at dec > 24 deg in the frequency range 42-66 MHz, reaching the sensitivity of 1 mJy/b and the resolution of 15 arcsec. Finally, I will outline the plans for the expansion of the LBA surveys with LOFAR 2.0 through the LBA LOFAR Community Sky Survey (LLoCuSS) project.
Speaker: Francesco de Gasperin (IRA INAF) -
32
The awakening of the WEAVE-LOFAR survey
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 of the Universe, and the formation and evolution of radio galaxies and (proto)clusters. After long delays, the survey is now ready to start, with the first IFU data available and the first MOS science verification observations taken. In this talk, I will provide a recap of the WL survey plans and science goals, with an emphasis on what the community can expect from the first year of the survey.
Speaker: Anniek Gloudemans (NSF’s NOIRLab) -
33
The LOFAR Two-metre Sky Survey
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 an update on LoTSS including survey progress, challenges, plans for the next data release and ambitions to build upon LoTSS once the upgrade to LOFAR is complete in 2025.
Speaker: Timothy Shimwell (ASTRON) -
34
The LOFAR LBA Virgo Cluster Survey
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 these interactions, since they allow us to probe the ram-pressure stripped tails, compressed magnetic fields and AGN-injected plasma.We previously completed a LOFAR HBA survey of the Virgo cluster, detecting 112 cluster member galaxies. We are currently carrying out follow-up surveys with the LOFAR LBA and MeerKAT of a >100 deg² region covering the cluster. Together, these surveys will improve the radio coverage of the system by more than an order-of-magnitude in depth, ranging from 42 MHz to 1.7 GHz.
In this talk, I will introduce these Virgo surveys, with a particular focus on the ongoing LOFAR LBA project. The major challenge of this project is the presence of the extremely bright central source M87 (= Virgo A, 2600 Jy) in the center of the cluster, imposing severe dynamic range limitations if not treated carefully. Furthermore, the low declination of the cluster (down to +4 deg) amplifies ionospheric systematics and reduces the signal-to-noise ratio. I will provide an overview on the specialised calibration strategies that are being developed to overcome these difficulties.
As an outlook for the scientific value of these data, I will present an analysis of highly extended (>0.6 deg scale) ultra-steep spectrum emission revealed for the Virgo galaxies M49 and NGC4365 by the LOFAR observations. This radio emission is ultra-steep spectrum (α < -1.5) and interpreted as past phases of AGN activity in these nearby massive early-type galaxies.Speaker: Henrik Edler (University of Hamburg) -
35
A cautionary tale about pipelines
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 discuss the recent addition of self-calibration to the LINC pipeline, added to improve the calibration on difficult fields such as the galactic plane or those containing bright compact sources. Based on this I will show examples of poor calibration, how things can go wrong early on and emphasize the need for (automated) quality control checks as early on as possible. Now that complex tools and pipelines are readily available, it is time to make our pipelines stricter in terms of what we accept for processing.
Speaker: Frits Sweijen (Durham University)
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31
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Session: Galaxy Clusters (1)Convener: Reinout van Weeren
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36
Optical identifications in LoTSS DR2: from Citizens to Science
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 can be robustly selected from the multiwavelength data.
Speaker: Prof. Martin Hardcastle (University of Hertfordshire, UK) -
37
Galaxy clusters at LOFAR's turning point: lessons learned and open questionsSpeaker: Andrea Botteon
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38
LOFAR-CHEXMATE study of radio halo clusters
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 new radio facilities at low frequencies, robust spatially resolved analyses on clusters are becoming available, providing new crucial information about different acceleration models.
As a first step of a wider systematical study, we analyzed a sample of 18 radio halos observed by LoTSS drawn from the CHEX-MATE project.
I find strong correlations between X-ray and radio brightness in every target. This relation is (almost) always sub-linear indicating a flatter distribution of the non-thermal component. In addition, by studying the varying radio-X relations found, I was able to test a simplified re-acceleration model and to put constraints on some of its parameters.
Finally, I will also present preliminary results of a tentative radio profile rescaling, as usually made for the thermal component of the ICM, searching for a universality of the halos radial profile.Speaker: Marco Balboni (DiSAT Insubria - IASF Milan) -
39
Decameter observations of Galaxy Clusters
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 are predicted to reveal the origin and nature of the population of these seed electrons. Radio observations below 30 MHz are very rare, however, due to the severe perturbing effects of the ionosphere. Recent calibration innovations with the LOw Frequency ARray (LOFAR) have enabled us to study galaxy clusters with high sensitivity below 30 MHz. This represents more than an order of magnitude improvement over previous decameter studies, both in terms of resolution (45 arcseconds) and sensitivity (12 mJy RMS noise). We have identified four fossil plasma sources corresponding to galaxy clusters in the region surveyed. These rare sources are believed to contain old, possibly re-energised, radio plasma originating from previous outbursts of active galactic nuclei. Notably, two of these sources display the steepest radio spectral index among all the sources detected (ɑ=-1.8 and -1.4). This has profound consequences for the understanding of the origin of non-thermal plasma in galaxy clusters.
Speaker: Christian Groeneveld (Leiden Observatory) -
40
Can we use LOFAR to estimate SFR of Low Surface Brightness Galaxies?
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 are considered to be dust-poor. However, the last analysis shows that a few per cent of them can be attenuated at the level of 0.8 magnitudes.
Our previous analysis shows that for main-sequence galaxies, LOFAR measurements can easily substitute infrared data to constrain the star formation rate through the spectral energy fitting method. Can we use the same method to study dust-poor and faint LSBs?
In my talk, I will present our study on the NEP multiwavelength data using more than 1000 LSB galaxies with estimated LOFAR fluxes at 144 MHz.Speaker: Prof. KATARZYNA MALEK (National Centre for Nuclear Research, Poland) -
41
Bridging the Gap: From UV/IR to Radio in Infrared Bright galaxies via SED Modeling and Radio SFR Calibration
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 in detail the physical processes that could be associated with the hierarchical transformation of star-forming galaxies into elliptical galaxies.
I will present the results of detailed spectral energy distribution (SED) modeling of 14 local ultra-luminous infrared galaxies (ULIRGs) with outstanding photometric data from the literature covering ultraviolet-far-infrared and radio bands (~50 MHz to ~30 GHz). We employ the CIGALE SED fitting code for ultraviolet to far-infrared and radio SED modeling. For radio-only SED modeling, we use the UltraNest package, leveraging its nested sampling algorithm. Combining results from our previous study on 11 LIRGs, we discuss the global astrophysical properties of a sample of 25 starburst galaxies (z<0.5). Their radio spectra are frequently characterized by bends and turnovers, with no indication of ULIRGs exhibiting more complicated SEDs than LIRGs despite showing more signs of interactions. Including radio measurements in CIGALE modeling constrained the dust luminosity and star formation rate (SFR) estimates by more than one order of magnitude better than previously reported for starburst galaxies. We show that total and nonthermal radio luminosity at 1.4 and 4.8 GHz frequencies can be good estimators of the recent SFR for all LIRGs and those ULIRGS with insignificant AGN influence. A weaker but still significant correlation is observed between radio SFR at 1.4 GHz and old (averaged over 100 Myr) SFR based on SED modeling, indicative of multiple episodes of starburst activity during their lifetime. The thermal radio luminosity at 4.8 GHz is a better tracer of recent star formation than the thermal luminosity at 1.4 GHz.
Speaker: Subhrata Dey (Jagiellonian University) -
42
The influence of the ionosphere visible in the dynamic spectra of pulsars observed with PL612 LOFAR station
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 knowledge of the signal entering and passing through the ionosphere provides an additional and independent of standard techniques (GNSS) study of the ionosphere. What is extremely helpful is that the LOFAR system is an extremely sensitive tool for observing flux changes. This is exploited by observing bright sources such as CasA or CygA. See for example [2].
During the presentation, results of the analysis of pulsar data for the study of the ionosphere will be presented. Already published work related to the influence of the ionosphere on pulsar signals [3] have now been extended to include studies of ionospheric-related structures visible in dynamic spectra. At the same time, because the results of pulsar observations are often reduced to average profiles, the influence of the ionosphere is not considered when studying these objects. However, for pulsars with strong pulse fluxes, we can analyze the case of a sequence of single pulses or average the results over several periods.
As we cannot determine absolute fluxes from observations of individual LOFAR stations, dynamic spectra are constructed based on instantaneous S/N (signal to noise) values. Comparative analysis of such a signal with the results of TEC (Total Electron Content) measurements carried out by GNSS services and analysis of variability allow for determining the dynamics of changes in the direction of the observed source. To determine the dynamics of changes in the signal received by the LOFAR station, the PSI – Pulsar Scintillation Index calculation, based on S4 index described in [4,5] is used.
Initial data show the presence of quasi-periodic changes, which gives hope for the possibility of further analyzes related to TID structures and increase knowledge on spatiotemporal disturbances of the ionospheric plasma. We will also present the first correlation results between the dynamic spectra of selected pulsars observed simultaneously with polish PL612 and PL611 LOFAR stations.References:
1.M. P. van Haarlem et al., “LOFAR: The LOw-Frequency ARray,” A&A, 556 ,2013, A2, DOI: https://doi.org/10.1051/0004-6361/201220873
2. R. A. Fallows et al., “Broadband meter-wavelength observations of ionospheric scintillation”, J. Geophys. Res. SpacePhysics,119, 10,544–10,560, 2014 doi:10.1002/2014JA020406.
3. L.P. Błaszkiewicz et al., “Finding the Ionospheric Fluctuations Reflection in the Pulsar Signals’ Characteristics Observed with LOFAR”. Sensors.; 21(1):51, 2021, DOI: https://doi.org/10.3390/s21010051.
4. P. Flisek et al., "Towards the possibility to combine LOFAR and GNSS measurements to sense ionospheric irregularities", J. Space Weather Space Clim. Vol. 13, 2023, DOI: https://doi.org/10.1051/swsc/2023021
5. B. Forte et al., Interpretation of Radio Wave Scintillation Observed through LOFAR Radio Telescopes, Astroph. Journal, Supplement Series, Vol. 263, Issue 21, 2022, DOI: 10.3847/1538-4365/ac6debSpeaker: Leszek Błaszkiewicz (Space RadioDiagnostic Research Centre, University of Warmia and Mazury in Olsztyn, Poland) -
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LOFAR-BG – the South-easternmost station of LOFAR ERIC: status update
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 software, hardware and human resources developments towards building LOFAR-BG.
Speaker: Antoaneta Antonova (Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences)
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10:30
coffee / tea / poster
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Session: Galaxy Clusters (2), Planets (1)Convener: Andrea Botteon (INAF-IRA)
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Tracing large-scale gas outflows from spiral galaxies in clusters with LOFAR
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 observations of galaxy clusters using LOFAR have revealed that an increasing number of spiral galaxies host radio-continuum tails which can extend for tens of kpc outside of the stellar disk. These tails are caused by the large-scale ISM outflows that are induced by the ram pressure. The gradients in the synchrotron emission, produced by the relativistic electrons embedded in the stripped ISM clouds, can constrain the velocity of the ISM outflows from the stellar disk. To test this hypothesis, a semi-empirical model was developed based on the pure synchrotron cooling of a radio plasma moving along the stripping direction with a uniform velocity. This model can reproduce the multi-frequency radio continuum emission of the ram-pressure-induced outflows. In an exploratory study on seven galaxies in Abell 2255 (z=0.08012), deep LOFAR and uGMRT observations at 144 and 400 MHz were used to showcase the results. The model successfully reproduces the observed properties of the radio-continuum tails, with projected outflow velocities ranging from 160 to 430 km/s. This new piece of information can help us understand the poorly-known physics of the interplay between the stripped ISM and the surrounding ICM in the stripped tails of these galaxies.
Additionally, this semi-empirical model can expand the use of radio observations of ram-pressure-stripped galaxies in clusters and groups. With the advent of SKA, the availability of these observations is expected to grow over the coming years. By combining deep radio, X-ray, and optical observations, we will be able to quantitatively characterize the role of ram pressure stripping in quenching the galaxies in dense environments.Speaker: Alessandro Ignesti (INAF-Padova) -
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The high resolution view of radio phoenices
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 passage of a shock wave. However, their precise origin and connection to shocks is still uncertain.
Radio phoenices are typically characterised by an irregular and filamentary morphology with an ultra-steep radio spectrum ($\alpha\ge1.5-2$). To investigate in more details the radio morphology of these sources we have decided to exploit the low frequency signal and high resolution of LOFAR VLBI data at 144 MHz.
In this talk, I will present for the first time the LOFAR high resolution images of the clusters A1914 and A566.
At sub-arcsecond resolution the emission of the radio phoenix in the cluster A1914 appears composed by two sub-structures, that could be remnant radio lobes. Many filaments have been detected connecting the two components or branching out from them. As the filaments in A1914 are very tangled, we speculate that the filamentary structure becomes more complex with time.
The radio phoenix in the cluster A566 also presents filamentary emission resembling the ``mushroom-shape'' structure observed in M87 (Owen et al. 2000) and in the galaxy group Nest200047 (Brienza et al. 2021).
The detection of filaments within radio sources is becoming frequent thanks to the high resolution and sensitivity observations available nowadays (e.g. Ramatsoku et al. 2020, Rudnick et al. 2022, Brienza et al. 2022). Given the variety of physical conditions in which these structures are observed, their formation should be connected to the dynamics of the magnetized plasma. Inquiring the origin of these filaments could therefore help us to make a step forward on the comprehension of radio phoenices formation.Speaker: Nadia Biava (Thüringer Landessternwarte (TLS)) -
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The age of filaments
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 dynamically important, as we now begin to learn. The turbulent fields can also be probed with Faraday rotation measurements. In this talk I describe a wide range of new observations that show that we are entering a new era of radio astronomy. A comparison with the latest generation of MHD simulations tells us about turbulence on a large range of scales.
Speaker: Marcus Brüggen (Uni Hamburg) -
47
A periodic radio transient found with LOFAR
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. 2022, Hurley-Walker et al. 2002, Hurley-Walker et al. 2023). Both magnetic white dwarfs and magnetar, in isolation or in binary systems, have been invoked to explain these types of objects. However, there is no consensus on the progenitor for this type of emission.
Our transient seems to fit with this long-period radio transient source class in a lot of aspects. However, in contrast to the previous detections, our transient lies far off the galactic plane and has an optical counterpart. This potentially confirms that this type of emission could originate from compact object binaries. This talk will be a broad description of the source, including the radio and multi-wavelength follow-up observations and the conclusions we can draw about the progenitor system.Speaker: Iris de Ruiter (University of Amsterdam/Anton Pannekoek Institute for Astronomy)
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12:15
Lunch (Pesthuis)
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Session: Planets (2), Transients and Pulsars (1)Convener: Jason Hessels (ASTRON & University of Amsterdam)
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48
Catching the wisps: constraining mass-loss rates of cool stars at low frequencies
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 indirectly, for example from astrospheric Ly$\alpha$ absorption. In this talk, I will present a more direct method to constrain the mass-loss rate of a star using detections of low-frequency coherent radio emission, exploiting the lack of free-free absorption to place upper limits on the stellar mass-loss rate. We apply this method to M dwarfs detected with LOFAR at 120 MHz and find upper limits down to 4 times the solar mass-loss rate, independent of distance. While these limits are already competitive with other methods, we expect to reach upper limits of less than the solar mass-loss rate in the near future.
Speaker: Sanne Bloot (ASTRON, Kapteyn Astronomical Institute) -
49
Hide and seek: Using LOFAR to hunt for hot Jupiters at decameter wavelengths
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 frequencies. Besides many efforts, direct imaging of radio exoplanets has not been successful until today, with only a handful of tentative detections. The Low-Frequency Array (LOFAR) is ideally suited for this task because it can observe at frequencies below 40 MHz and has high sensitivity. However, imaging at such low frequencies is challenging due to high interference levels and rapidly varying ionospheric conditions. To overcome the technical challenges of imaging below 40 MHz, I will present a new pipeline that corrects for all the known instrumental and ionospheric effects. Then, I will show the deepest images down to 15 MHz of a radio exoplanet candidate field. A clear detection of Tau Bootes b would be the first in the field of radio exoplanets and a step forward for imaging at low frequencies. I will end with a brief overview of the learned lessons and introduce an ongoing major LOFAR upgrade that will facilitate deeper imaging down to 15 MHz.
Speaker: Cristina-Maria Cordun (ASTRON) -
50
The collaboration between the University of Warmia and Mazury and the Poznan Supercomputing and Networking Center: A significant milestone in our endeavor to conduct high-resolution mapping of compact galaxies utilizing the LOFAR-VLBI pipeline.
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 Compact Steep Spectrum (CSS) sources serve as precursors to large-scale radio galaxies of the FRI/FRII type. As these compact sources evolve, their radio jets endeavor to extend beyond their host galaxies, developing into large-scale structures. However, statistical analyses have uncovered a significant surplus of small, low-luminosity sources compared to powerful, fully developed, luminous radio galaxies. This suggests that not all GPS and CSS sources can evolve into large-scale structures; some exhibit intermittent, recurrent activity over periods of several thousand years.
Through the application of Very Long Baseline Interferometry (VLBI) techniques and extensive multi-epoch, multi-frequency observations, we have been able to detect even the faintest objects, acquiring their luminosities and fast-evolving spectra. These spectra serve as primary evidence of rapid changes occurring within young AGNs. Additionally, extensive scattered emission surrounding the source may serve as another indication of such phenomena, representing remnants of previous phases of activity where jet propagation was hindered and dispersed on smaller scales.
Access to the sky at extremely low frequencies, facilitated by instruments like LOFAR, now enables us to capture relic emissions, providing a unique opportunity to study the life cycle of radio sources, even on smaller scales.
However, imaging these objects necessitates substantial computational resources and time. In our work, we aim to present the results of our initial attempts to image these objects in pursuit of the aforementioned emissions, leveraging the latest available software in collaboration with the Poznań Supercomputing and Networking Center.
Speakers: Aleksandra Wołowska (University of Warmia and Mazury), Mateusz Olech (Space RadioDiagnostic Research Centre, University of Warmia and Mazury in Olsztyn, Poland) -
51
Fast transients < 300 MHz
Low-frequency (~< 300 MHz) observations of impulsive transients allow precise measurements of propagation effects (dispersion, scatter-broadening and Faraday rotation) that probe the local environments of the sources that produce these transients. The detection of bursts from repeating fast radio burst (FRB) sources 20180916B and 20181030A with the LOFAR telescope indeed has put the tightest constraints on free-free absorption local to these two sources. It has also revealed a chromaticity in the periodic activity of FRB 20180916B. Moreover, one burst extending down to the bottom of the LOFAR High-Band Antennas (HBA) at 110 MHz suggests that FRB emission is detectable at even lower frequencies. LOFAR 2.0 will have a much-improved correlator network bandwidth that allows for the multi-casting of station data and the production of order thousand tied-array beams for rapid sky mapping. We have been developing the EuroFlash survey, that will piggyback on all LOFAR observations and independently beamform and search for transients on a dedicated compute cluster. A combination of targeted and untargeted searches will run 24/7 and year-round and will greatly increase the yield of fast transients at low frequencies. It will reveal any frequency-evolution in the population of FRBs through comparison with the CHIME/FRB survey and surveys at L-band, and it may well uncover a completely new class of fast transients that only manifests at low frequencies. Inclusion of the international stations with baselines up to 1000 km will allow for ~arcsecond localization of bursts. In this talk, I will review low-frequency observations of fast transients and give an update of the commissioning of EuroFlash on LOFAR 2.0.
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Galaxy groups at the lowest frequencies: a combined LOFAR-uGMRT view of A1213
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 the lowest radio frequencies. This is essential since, because of the shape of the synchrotron spectrum, we are potentially able to assess the effects of past AGN outbursts on the host environment and how it affected its evolution.
In this talk, I will present new observations of Abell 1213, a galaxy group that recently fell under the spotlight for the presence of a long tail of diffuse emission in the radio band whose origin is hard to explain. Our study includes LOFAR and uGMRT proprietary data at 54 and 380 MHz, as well as LOFAR VLBI images from LoTSS at 144 MHz. The long tail extends for ~500 kpc Eastwards from the AGN and shows multiple sub-components. While a recent study gave a tentative classification as a radio relic, we show spectral index maps that hint a different origin, most likely linked to old AGN plasma ejected during past outbursts. The analysis of the thermal emission from the Intra-Group Medium (IGrM) support this hypothesis, as it hints to a physical connection with the non-thermal component. By sampling the spectral index along the extended tail and the AGN, we show that within the first 150 kpc the source shows an inverted spectrum. Finally, from LOFAR images there are hints of a faint, diffuse component with an extremely steep spectrum (𝛼<-3) which surrounds the central AGN, and whose nature is still unclear.Speaker: Thomas Pasini (Istituto di Radioastronomia IRA-INAF) -
53
Title: Thermal and non-thermal emission in merging galaxy groups NGC7618/UGC12491
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 poster, I will report ongoing work based on the combination of radio multi-frequency observations (LOFAR 144 MHz, GMRT at 323 and 608 MHz and JVLA in L band) and X-ray Chandra data of this rare major group merger. In the radio the two groups show different features, with NGC7618 being characterized by prominent extended radio emission at its center (on scales up to 90 kpc), and UGC12491 showing only a marginal indication of faint diffuse emission at its center. The spectral mapping of the radio emission in NGC7618 has a complex distribution, suggesting ongoing interplay between non-thermal components and the surrounding thermal gas, likely involving particle re-acceleration. By combining radio and X-ray properties we aim to understand the origin of the diffuse source in NGC7618 and the reason of its different radio properties with respect to the companion UGC12491.
Speaker: Davide Matteo Brustio (University of Bologna) -
54
Unveiling the fine structure details of the radio relics in MACS J1752.0+4440
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 as a double-relic system, in which the near to the plane of the sky merger axis allows for a simple geometry and minimalized projection effects.
Recent high-resolution studies of radio relics revealed their filamentary structure, exposing the presence of many small-scale substructures, generating morphologies that are challenging to explain with simple systems. The origin of these filaments is yet unknown, and can be connected with complex shock surfaces or a complex magnetic field structure.
In this work, we studied the double-relic galaxy cluster MACS J1752.0+4440 at four frequencies: 144MHz (LOFAR), 416MHz and 650MHz (uGMRT) and 1.6GHz (JVLA), performing a high-resolution spectral and curvature study of both relics, observing a filamentary substructure along the North-East (NE) relic. The surface brightness and spectral index profiles highlight the presence of the filament along the NE relic. Color-color plots show that no spectral curvature is observed in the bandwidth. Furthermore, the integrated spectral index is surprisingly flatter than what predicted by DSA theory.
These features cannot be reproduced with simple assumptions and are likely the result of either a complex Mach number shock surface or strong projection effects at the shock location, which suggest caution is needed on the interpretation of double-relic systems.Speaker: Maicol Della Chiesa (UNIBO)
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15:00
Coffee / tea / posters
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Session: Transients and Pulsars (2)Convener: Antonia Rowlinson
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Pulsar Timing Arrays -- The impact of LOFAR and NenuFAR
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 convincing evidence for a GW signature in the pulsar data collected to date.
This groundbreaking result is not a confirmed discovery yet, as its signal-to-noise does not reach the safe 5$\sigma$ threshold requested for a robust detection. This is mainly because of the numerous other signals that are present in pulsar data, such as intrinsic instabilities of the pulsars and the plasma-induced noise.
To increase the significance of the discovered signature, the EPTA is leveraging on the extraordinary low-frequency pulsar datasets that have been collected with LOFAR and NenuFAR. These are demonstrating to be crucial to identify signals induced by the interstellar medium and the Solar wind.
In this talk I will revise the current status of PTA experiments and the most significant results coming from the combination of LOFAR, NenuFAR and the EPTA data, as well as the role of LOFAR2.0 in the next stages of PTA science.Speaker: Caterina Tiburzi (INAF-OAC) -
57
The Crab Nebula
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 observations allow us to measure the expansion of the pulsar wind nebula, which resulted from a supernova explosion in 1054. More interestingly, our map shows new absorption features in a filament southwest of the pulsar, including knots with a spectral index of approximately 3 (for $S_\nu \propto \nu^\alpha$). I will discuss free-free absorption and synchrotron self-absorption as the possible origins for the observed absorption features, and their implications for the physical conditions in the knots.
Speaker: Maria Arias (Leiden Observatory) -
58
EuroFlash: a commensal fast transient search machine for LOFAR2.0
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 physical origin(s) of these enigmatic signals and to use them as unique and powerful probes of the otherwise invisible matter and magnetic fields that lie between stars and galaxies. LOFAR2.0 offers us a new way to explore the sky as never before possible by giving a novel, wide-field view of the lowest radio frequencies observable from Earth at both high time and angular resolution. To turn LOFAR2.0 into a fast transient search machine, we are constructing the EuroFlash backend, which will receive a commensal stream of raw station data (and maybe even raw antenna data) to search for milliseconds- to seconds-duration transients in all observations. In this talk, I will outline the scientific case, technical approach, and project status.
Speaker: Jason Hessels (ASTRON & University of Amsterdam)
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Evening session: Boat tour and conference dinner
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Session: Sun and Space Weather (1)Convener: Pietro Zucca (ASTRON - Netherlands Institute for radio astronomy)
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Solar research with LOFAR telescope
Astronomers have been observing the Sun at radio wavelengths for about 80 years. Of their particular interest are studies of various solar radio bursts and fine structures. This research is crucial for better understanding of the plasma processes occurring in the corona, as well as their diagnostics and verification of the obtained results with laboratory plasma studies. Recently a new generation of radio telescopes such as LOFAR has significantly improved the quality of radio observations of the Sun. Apart from the sensitivity, high time and frequency resolution of the dynamic spectra, LOFAR allows also an imaging of the radio sources and tracking of their positions through the solar corona. LOFAR can also be used to monitor radio bursts for space weather purposes like for example type II radio bursts related to CMEs. In this talk, I will present an overview of recent progress and current status of amazing Solar and Space Weather studies performed with LOFAR telescope.
Speaker: Bartosz Dąbrowski -
60
Observations and simulations of the shortest solar radio bursts with LOFAR
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 mass ejection (CME). The CME perturbs the field geometry, leading to increased spike emission likely due to frequent magnetic reconnection. LOFAR imaging reveals that on average, both burst types have a similar source size, fast expansion at millisecond scales, superluminal sky-plane centroid velocities, and intensity contours that overlap for cotemporal bursts. Combined with previous observations above 1 GHz, the average decay time and source size estimates follow a $\sim1/f$ dependence over three decades in frequency, similar to radio-wave scattering predictions. Both time and spatial characteristics of the bursts between 30-70 MHz are consistent with radio-wave scattering with a strong anisotropy of the density fluctuation spectrum. Consequently, the site of the radio-wave emission does not correspond to the observed burst locations and implies acceleration and emission near the CME flank.
Speaker: Daniel Clarkson (University of Glasgow) -
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Evolution of fundamental and harmonic sources in LOFAR type III radio burst images
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 the location remains largely fixed since it is determined by where in the solar corona the local plasma frequency matches the observing frequency. But from time to time the source changes its position, with dual structures during the transition. We interpret this as signatures of fundamental and harmonic emission, the latter originating from a higher location in the corona so that the local plasma frequency there matches half of the observing frequency. Fundamental-harmonic pairs, e.g. fundamental emission at 35 MHz and harmonic emission at 70 MHz, should originate from the same plasma volume. Differences in their positions and intensity variations are expected since radio wave transport effects in the corona, like scattering and refraction, should affect fundamental more than harmonic emission. Analyzing such differences therefore allows for quantifying these effects.
Speaker: Christian Vocks (Leibniz-Institut für Astrophysik Potsdam (AIP)) -
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Ionospheric irregularities assesed throught LOFAR and GNSS observations
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 particular,
intensity scintillation is visible when the signal travels through plasma density irregularities with small spatial scales.
Ionosphere conditions are observed and studied with use of the Global Navigation Satellite Systems (GNSS), where
ground-based receivers observe the radio signals coming from the satellites. Moreover, the radio telescopes (such as
LOFAR – LOw Frequency ARray) are being increasingly utilised for ionospheric studies in recent years. Such multi-
instrumental approach has a significant impact on the field of ionospheric studies and is expected to bring new insight
ine ionospheric plasma dynamics as well as in ionospheric radio wave propagation. The mutual observations with
GNSS and LOFAR can be utilised to determine the properties of the ionosphere irregularities as it has not been done
before.
Ionosphere scintillation can be quantified by means the S 4 intensity scintillation index (the standard deviation of the
normalized signal intensity). The S 4 index is attributable to ionospheric irregularities in the inertial sub-range where
electron density irregularities can induce scintillation.
Ionospheric propagation effects have an impact on other observations, such as from pulsars. The combination of
ionospheric observations from different instruments such as LOFAR and GNSS helps describe the properties of
ionospheric irregularities and their propagation effects in a way that has not been done before. This contribution
discusses the interpretation of ionospheric observations measured, for example, by means of LOFAR and GNSS.Speaker: Prof. Andrzej Krankowski (University of Warmia and Mazury in Olsztyn) -
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Observing the Sky with a Single LOFAR Station: Impact of Ionosphere on Position Measurements and Observation of related ionospheric structures
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 station operates at the frequency range of 10 - 240 MHz, enabling the observations of astronomical sources at the lowest frequencies available on Earth.
Due to its design and operating frequencies, the LOFAR radio telescope is not limited to radio-astronomical observations. In that context, the Space Research Centre of the Polish Academy of Sciences utilises the station to monitor the ionosphere and observe the effects of space weather.
The previous studies confirmed the feasibility of measuring ionospheric gradients using a single LOFAR station by observing the changes in radio source position.In our work, we show that the ionosphere significantly impacts the radio source position that is directly connected to the horizontal ionisation gradient.
To investigate this gradient, we measured the positions of the strongest astronomical radio sources – called the A-Team (CasA, CygA, TauA, and VirA) – observed in the LOFAR frequency range (10 – 90 MHz). Due to its high time resolution (1 s), the method allows the observation of small-scale structures, which can be related to ionospheric scintillation. Moreover, it enables the observation of medium-scale structures moving over the LOFAR station.
In the following work, we present selected cases of observed structures recorded moving over the station during the observations.Speaker: Dr Dorota Przepiórka-Skup (Centrum Badań Kosmicznych Polskiej Akademii Nauk)
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10:30
Coffee / tea / posters
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Session: Sun and Space Weather (2), Cosmology (1)Convener: Andrzej Krankowski
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64
LOFAR observations of highly defined symmetric quasi-periodic ionospheric scintillations
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 channel scintillation observations. Here we present LOFAR broadband ionospheric scintillation observations of exceptionally well defined symmetric quasi-periodic scintillations. Two case studies are shown, one from 15th. December 2016, and one from 30th. January 2018, in which well-defined main signal fades and secondary diffraction fringing are observed. In particular, the broadband observing capabilities of LOFAR permit us to see considerable frequency dependent behaviour in the QPS which, to our knowledge, is a new result. We extract some of the clearest examples of scintillation arcs reported in an ionospheric context, from delay-Doppler spectral analysis of these two events. These arcs permit the extraction of propagation velocities for the plasma structures causing the QPS ranging from 50-200 ms-1, depending on the assumed altitude. The spacing between the individual plasma structures ranges between 5-20 km. The periodicities of the main signal fades in each event and, in the case of the 2018 data, co-temporal ionosonde data, suggest the propagation of the plasma structures causing the QPS is in the E-region. Each of the two events is accurately reproduced using a Gaussian perturbation phase screen model. Individual signal fades and enhancements were modelled using small variations in total electron content (TEC) amplitudes of order1 mTECu, demonstrating the sensitivity of LOFAR to very small fluctuations in ionospheric plasma density. To our knowledge these results are among the most detailed observations and modelling of QPS in the literature.
Speaker: Hannah Trigg (University of Birmingham) -
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Modeling and experimental investigations for Modern Radio-Diagnostics of the Ionosphere using LOFAR and GNSS Data
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, including traveling ionospheric disturbances (TIDs), from high and low latitudes to mid-latitudes is expected during current period of increased solar activity 2023-2025. At the University of Warmia and Mazury in Olsztyn, Poland, the project “Modern Radio-Diagnostics of the Ionosphere using LOFAR and GNSS Data” National Center of Science (Poland) is currently underway. Its goal is to consolidate ongoing experimental and theoretical research, including data and modelling on excitation and scattering of HF EMW on wave plasma structures in unstable nonlinear space (ionospheric and interstellar) plasma. Example of such structures are ones connected with Hunga-Tonga volcano eruption. Possible applications include ionospheric diagnostics, including catastrophic space weather phenomena, as well as the identification of new mechanisms of nonlinear wave interactions in space plasma. Experimental studies and sampling of LOFAR and GNSS data are now aimed at identifying structures with characteristic TID parameters, presumably associated with atmospheric gravity waves (AGW), including corresponding ionospheric excitations caused by the solar terminator. It is planned to present theoretical results obtained from models of (1) scattering of HF EMW on ionospheric plasma structures, based on the method of complex geometric optics (CGO) and (2) ionospheric plasma structures, and work is currently underway to include wave excitations caused by solar terminator. The new results will be presented: (a) results of multi-beam scattering of HF EMW on plasma structures were obtained; (b) for frequencies several times higher than the cutoff frequency, when scattered by a plasma structure moving at a speed of the order of (0.3-0.1) km/s, Doppler frequency shifts have different signs for ordinary and extraordinary waves; (c) as horizontal size of plasma structures decreases, difference in Doppler shifts of ordinary and extraordinary waves increases. [1] M. P. van Haarlem et al., A&A, 556 ,2013, A2 DOI: https://doi.org/10.1051/0004-6361/201220873 [2] R.A. Fallows et al., JSWSC, 2020, 10, 10, doi.: 10.1051/swsc/2020010. [3] B. Forte et al., Astrophysical Journal, Supplement Series, 2022, 263, 36, doi.:10.3847/1538-4365/ac6deb. [4] P. Flisek et al., JSWSC, 2023, 13, 27, doi.: 10.1051/swsc/2023021. [5] Dorrian, G. et al. (2023). Space Weather, 21, e2022SW003198. https://doi.org/10.1029/2022SW003198
Speaker: Yuriy Rapoport (University of Warmia and Mazury in Olsztyn) -
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Radio eyes for the Sun, Heliosphere and Ionosphere: Status and plans for the LOFAR2.0 era.
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 of LOFAR Space-weather) project.
LOFAR's current work in solar physics involves high-resolution imaging and dynamic spectral analysis, enabling detailed observations of solar radio bursts and other coronal heliosphere and ionosphere phenomena. These observations are critical for understanding the mechanisms behind solar activity and improving our predictive models of space weather events. The LOFAR IDOLS station, dedicated to space-weather science, has been instrumental in advancing this work. It currently provides continuous monitoring of the ionosphere and Sun, tracking disturbances that can affect space weather on Earth, but also the astronomical observations of LOFAR itself.
The LOFAR2.0 upgrade promises to enhance these capabilities significantly. Plans include improving the sensitivity and spatial resolution of the array, and the simultaneous observations in LBA and HBA, which will allow for even more precise and broad imaging and tracking of solar phenomena. This will enable researchers to identify and study the fine structures within the solar corona and track the development of space weather events with greater accuracy.
Furthermore, the LOFAR IDOLS project is set to continue observation during the period of transition to LOFAR2.0 enabling us to test the monitoring capabilities.
In conclusion, the LOFAR2.0 era heralds a new chapter in solar and space weather research. With the ongoing work and future plans for the LOFAR IDOLS station and LOFAR2.0 observations, we are ready to gain deeper insights into the Sun's influence on our space environment and to develop more robust forecasting capabilities for space weather phenomena.
Speaker: Pietro Zucca (ASTRON - Netherlands Institute for radio astronomy) -
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Cosmological studies with LOFAR surveysSpeaker: Catherine Hale
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The Cosmic Radio Dipole: Bayesian multi-survey estimation
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 catalogues, as well as, for the first time, the LoTSS-DR2 and RACS-mid radio source catalogues. The estimator provides a more accurate description of the observations by accounting for multi-component radio sources. For the measurement, the radio dipole direction remains fixed to the CMB dipole direction. This study finds amplitudes that are in line with the CMB dipole expectation. However, it cannot be ruled out that there is an excess radio dipole.
Speaker: Lukas Böhme (Bielefeld University)
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Lunch (external)
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Session: Cosmology, EoR (2)Convener: Dominik Schwarz
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Observing the 21-cm signal from the Epoch of Reionization and the Cosmic DawnSpeaker: Kariuki Chege
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Advanced modeling of bright radio sources for LOFAR 21-cm power spectrum analysis: the Cygnus A and 3C196 cases
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 their removal. This modeling is essential in scenarios where bright sources are close to the observing direction, such as in the 3C196 field, as well as in situations where they are far from the main field of view, as observed with A-team sources in the North Celestial Pole (NCP) field. In this talk, I present a new high-resolution model of Cygnus A, the brightest of the A-team sources, using LOFAR-HBA observations. This model improves previous models by incorporating physical spectral information through the forced-spectrum method during multi-frequency deconvolution. I will demonstrate how this new model effectively lowers the upper limits on the LOFAR 21-cm power spectrum extracted from the NCP, thus enhancing the quality of foreground subtraction. Furthermore, I introduce the first upper limits at z~9 from the 3C196 field, based on a single night of observations with LOFAR-HBA. The modeling challenge here is presented by 3C196, a ~100 Jy source at the center of the field, which helps the calibration but must be meticulously subtracted to minimize its residuals. Using a LOFAR-VLBI model of 3C196 and a processing pipeline different from the one used for the NCP, we achieve promising results that highlight the accuracy and potential of LOFAR for cosmological 21-cm signal observations.
Speaker: Emilio Ceccotti (Kapteyn Astronomical Institute) -
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Beyond Just Beam Error: Direction-Dependent Calibration Challenges Far from the Phase Center
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 and beam model for finding element gains which minimize the difference between observed and modeled gains. However, these standard calibration tools struggle with precision calibration when small beam modelling errors and relatively bright sources distant from the phase center are present. The resulting errors are currently limiting the attainable sensitivity in LOFAR Epoch of EoR observations. This may be due to the highly spatially, spectrally and temporally varying nature of the instrument beam of minimally redundant arrays outside of their primary beam. Our objective is to thoroughly characterize this problem using LOFAR simulations and to explore potential solutions. This presentation will outline our findings and discuss their implications for improving direction-dependent calibration in radio astronomy.
Speaker: Stefanie Brackenhoff (Kapteyn Astronomical Institute)
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Coffee / tea / poster
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Session: LOFAR ERIC Celebration
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The LOFAR ERICSpeaker: Jacqueline Mout
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Evening session: Reception at the city hall (Stadhuisplein 1)
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Session: Galaxy Clusters (2), OtherConvener: Emmy Escott (Durham University)
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Intercontinental decametric VLBI
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 case of success, we can study the decametric emission from Jupiter at the finest scales. I will report on the progress, hopefully show first very preliminary results, and explain what can be done in the case of Jupiter, based on earlier European interferometry.
Speaker: Olaf Wucknitz (Max-Planck-Institut für Radioastronomie) -
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Unintended electromagnetic radiation from satellite constellations
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 discuss its impact on various science cases and possible strategies to mitigate it.
Speaker: Cees Bassa (ASTRON) -
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A view on cluster-scale diffuse radio emission at high redshiftSpeaker: Gabriella di Gennaro
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10:30
Coffee / tea / posters
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Session: AGN (1)Convener: Gabriella Di Gennaro (Hamburg Observatory)
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The LOFAR-eFEDS survey: The incidence of radio and X-ray AGN
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 in the incidence of X-ray AGN as a function of λEdd. However, the story is more perplexing in the case of radio AGN, especially when considering different radio morphologies, as their incidence as a function of λJet shows a residual mass and jet power dependence. Interestingly, these effects cannot be explained by more powerful radio AGN residing in more dense environments (or more massive dark matter haloes). Finally, we demonstrate that this statistical incidence approach is a powerful way to probe the fundamental accretion physics, in particular the disk-jet connection, in varying accretion modes.
Speaker: Zsofi Igo (MPE) -
79
The Mass Assembly and Quenching of Radio AGN Host Galaxies
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 continuum - star formation relation and quantify its intrinsic scatter, then use them to classify 618 radio AGNs with excessive radio luminosities of $L\rm _{144MHz}>10^{21}\,W\,Hz^{-1}$. Massive quiescent galaxies dominate the radio AGN hosts, but the quenching level of radio AGN hosts shows no correlation with the jet luminosity. The mass assembly histories from stellar population synthesis agree with cosmological simulations incorporating radio-mode AGN feedback models. We observe that radio AGN hosts tend to grow faster, particularly evident in their central regions. By stacking the spectra in different radial bins of radio AGN hosts and their control sample, we find subtle emission line excess features in the nuclear region of radio AGNs, potentially indicative of connections between radio jets and the nuclear interstellar medium.
Speaker: Gaoxiang Jin (Max Planck Institute for Astrophysics) -
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New constraints on the contribution of star formation and AGN activity in quasar radio emission from the LOFAR Two-metre Sky Survey
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, using an improved Bayesian parametric model that allows us to statistically separate the SF and AGN components in observed quasar radio flux density distributions. I will present new results based on the LOFAR Two-Metre Sky Survey Data Release 2, showing a quasar host galaxy SFR evolution that increases with bolometric luminosity and with redshift out to redshift ~4. The prevalence of radio AGN emissions increases with quasar luminosity, but has little dependence on redshift, indicating the AGN jet strength is mostly governed by local activities. Our new methodology and large sample size also allow us to investigate the role of parameters including quasar colour and black hole mass on quasar radio emission. I will show that the radio excess in red quasars is due to an enhancement in AGN-related emission, and that this radio enhancement occurs mostly in quasars with weak or intermediate radio power. I will also present a coherent picture of black hole mass impact on the quasar radio emission, where only the most massive black holes produce powerful jets that lead to excess in radio loudness.
Speaker: Bohan Yue (University of Edinburgh) -
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High-resolution low-frequency probes of X-ray emitting knots in blazar jets
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 IC/CMB, Synchrotron Self Compton(SSC) or second synchrotron peak. We aim to study a sample of blazars featuring X-ray emitting jets, the morphology of which can be sampled with LOFAR-VLBI. We present ongoing analysis and results on the first object in this sample, OJ287. The long international baselines of LOFAR allow us to spatially resolve the individual X-ray emitting jet knots at ~140MHz and to probe the previously inaccessible part of the low-energy electron population. In combination with shorter-wavelength radio in the VLA GHz regime and Chandra X-ray data, the LOFAR-VLBI data will help test and constrain the above-mentioned different emission models. Here, we present results from this project with a focus on the LOFAR-VLBI sub-arcsecond resolution image of the X-ray jet in OJ287, resolving the kiloparsec knots in the jet. Furthermore, we present broadband SED modeling analysis for these knots, thereby understanding the physical properties of the underlying electron population.
Speaker: Hrishikesh Shetgaonkar (Julius-Maximilians-Universität Würzburg)
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12:30
Lunch (Pesthuis)
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Session: AGN (2)Convener: Olaf Wucknitz (Max-Planck-Institut für Radioastronomie)
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82
Revealing the sub-arcsecond nature of radio galaxies in Abell 2255
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 strategies.
In this talk, I will present results from deep (64 hours) observations of the main radio galaxies in the galaxy cluster Abell 2255. The main focus will be on the “tails” of the most extended sources, and in particular on the spectacular wealth of filaments revealed in the Original Tailed Radio galaxy (Original TRG, Harris et al. 1980) combining high-resolution and sensitivity of the ILT: such structures represent unique tracers to study the interplay between the radio galaxies and the turbulent cluster environment.
I will then zoom out on the cluster scale showing the first wide-field, ILT image of the cluster with 8 hours of observations at 1.5” resolution. This represents an unprecedented opportunity for statistical and morphological studies to investigate the effect of cluster environment on a large sample of cluster member radio galaxies. I will discuss the technical challenges involved in the processing of such complex field and the calibration strategies adopted to deal with such extended sources.
Speaker: Emanuele De Rubeis (Università di Bologna (UNIBO) & Istituto di Radioastronomia (INAF-IRA)) -
83
Multi-frequency mapping and analysis of the largest giant radio galaxies
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 and spatial resolution. The advent of LoFAR in recent years has made such analyses feasible, offering superior sensitivity and resolution at low frequencies, which is crucial for constraining injection index in spectral ageing analysis. GRGs that surpass 2 Mpc (largest) in size are uncommon, constituting less than ~10% of the GRG population. Consequently, we have selected a sample of the largest and brightest GRGs, all exceeding 2 Mpc, totalling eight sources (7 GRGs, 1 GRQ). These were meticulously observed using our dedicated observations with LoFAR (21hr), uGMRT (47hr), and JVLA (7hr), covering a frequency range from 150 MHz to 10 GHz. We have carried out detailed spectral and dynamical age modelling over a wide range of frequencies using packages like Synage, BRATS, Dynage and RAiSE HD and also compare them. We will for the first time present detailed spectral ageing analysis of the largest giants using our deep mutli-frequency data spanning 150 MHz to 10 GHz, which allows us to reliably determine the break frequencies. Additionally, we also examine the comparison between dynamical and radiative ages of these sources. Using our multi-frequency high resolution deep radio maps we have also explored core properties and hotspot features. Interestingly, all GRGs in our sample exhibit a high axial ratio, and most have conical hotspots on both sides. In this oral presentation, I will present our meticulous work, encompassing the acquisition of multifrequency data, its subsequent analysis, and the comprehensive process of integrating these insights into detailed modeling to decipher the nature of the largest giants.
Speaker: Sagar Sethi (Astronomical Observatory of the Jagiellonian University) -
84
LOFAR Legacy 58 MHz Survey of the 3CRR Catalogue
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 and energetics. However, a lack of instruments with sufficiently long baselines (combined with short baselines) at frequencies below 1 GHz, or a lack of robust calibration strategies, has prohibited any highly-resolved radio galaxy studies in the MHz regime. Observing at these low frequencies using the Low Band Antenna (LBA) system has proven challenging. However, over the past few years, our team has developed tools and strategies to solve both instrumental and ionospheric systematic errors, producing thermal noise limited images. With this work we calibrate and image the observations of the entire 3C(RR) catalogue. The final goal is to obtain a flux-limited legacy catalogue of radio images with the following unique combination of characteristics: (I) an observing frequency of 60 MHz, (II) a high resolution (< 10′′), and (III) good sensitivity to large scale emission.
Speaker: Jort Boxelaar (INAF - IRA) -
85
Probing the Evolution of Radio Quasar Morphologies Across Cosmic Time with LoTSS
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 the distortions in high-redshift RLQs, suggesting a more bent and distorted appearance compared to their lower-redshift counterparts. These studies have pointed towards an epoch-dependent interaction of the radio jets with an evolving interstellar or intergalactic medium. Saikia (1989, ESO) has stressed the importance of comparing sources of similar sizes as small sources are often found to be more distorted due to the effects of both the external environment and orientation. In addition, the limitation in the size of the samples and the depth of the surveys has called for further investigation with larger and more diverse quasar populations.
Our study aims to systematically characterize the properties of these RLQs, such as sizes, bending angles, and degrees of distortion, and to compare these features across size bins and redshift bins. Employing newer and significantly larger samples will not only ensure more robust statistical analyses of sources within each bin but also enable a comprehensive analysis of morphological evolution and its dependence on cosmic time. Building on the insights from Barthel & Miley (1988) and Saikia (1989), we intend to explore the relationship between quasar distortion and linear size, the fraction of emission from the core, and the misalignment angles, all while accounting for potential projection effects and orientation biases. Notably, previous studies (e.g. Barthel & Miley (1988)), included sources with redshifts up to ~2.6. We intend to significantly extend this investigation to encompass much higher redshifts, an ambition now feasible due to the exceptional sensitivity offered by LoTSS, coupled with the availability of deep spectroscopic surveys like DESI/ HETDEX. This expansion into higher redshift domains promises to illuminate the evolutionary trajectory of RLQs across a broader expanse of cosmic time, enhancing our understanding of their growth and the dynamics in the early Universe.
We have undertaken a comprehensive study using the LoTSS (deepest wide-sky area low-frequency radio survey), which provides an unprecedented opportunity to extend this line of inquiry to a broader and deeper cosmological scale. LoTSS, with its superior sensitivity and resolution at low frequencies, allows for the identification of RLQs across all redshifts up to z~6 (as demonstrated recently by Gloudemans et al. 2022 A&A), encompassing a wide variety of radio morphologies, including Fanaroff-Riley type II (FRII) sources. Our preliminary analysis has already revealed 36 RLQs with Fanaroff-Riley type II (FRII) morphology with z>3 from a careful manual inspection of 3000 candidate RLQs from the LoTSS, marking the largest sample of its kind to date. These 36 high-z RLQs exhibit a range of sizes from 40 to 800 kpc, among which three qualify as giants—representing the highest redshift giants identified to date. Interestingly, 70% of the 36 RLQs predominantly display asymmetric morphologies, with the core being situated closer to one lobe than the other. This observation marks the first instance of such reporting for FRII RLQs and their properties within this previously unexplored redshift regime. Additionally, these sources provide us with a unique opportunity to further investigate the effect of inverse Compton scattering from the Cosmic Microwave Background (CMB), given their location at very high redshifts. This aspect of our study is particularly significant, as it offers insights into the interaction between the relativistic electrons within the quasar jets and the increasingly energetic CMB photons in the early Universe. Understanding this interaction is crucial for elucidating the energy loss mechanisms and the overall impact on the observed radio morphology of RLQs across different epochs.
While the automated identification of large samples of Fanaroff-Riley type II (FRII) radio sources has demonstrated promising progress through the application of machine learning techniques, the automated measurement of sizes, distortion, and bending angles of radio sources remains a challenge. Consequently, these tasks still necessitate meticulous manual inspection and measurements, a process that is both time-consuming and labour-intensive. In response to this, our efforts are being concentrated on developing a semi-automated package designed to streamline the classification and measurement of the properties of thousands of sources. We have already conducted tests and identified properties for nearly 1000 sources, with ~0.3 ≤ z ≤3. This innovative approach aims to expedite the creation of an extensive sample of FRII RLQs from the LoTSS (aided by FIRST and VLASS), encompassing the widest possible range of redshifts. Through this, we anticipate significantly enhancing the efficiency and accuracy of our analyses, paving the way for important discoveries.
In the near future, our sample will benefit from data obtained from high-frequency surveys (matched in sensitivity and resolution), enabling us to ascertain the radio spectral properties and analyze their relationship with redshift.
By using the capabilities of LoTSS, this study promises to significantly advance our understanding of the evolutionary trajectory of RLQs and their interaction with the cosmic environment. The insights gained could have profound implications for models of galaxy evolution, the physics of radio sources, and the nature and evolution of the Universe's large-scale structure. By meticulously analysing the largest sample of FRII RLQs to date, we anticipate uncovering nuanced trends and relationships that were previously unattainable. In the oral presentation, we will present the results mentioned above, delve into their implications, and highlight the significant progress made in our study.
Speaker: Pratik Dabhade (Instituto de Astrofísica de Canarias (IAC, Spain)) -
86
A statistical study of the most extreme star factories and gorging black holes
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 are at the most extreme. Thanks to the well-established far-infrared to radio correlation, we make use of the high angular resolution of the radio observations from telescopes such LOFAR, Meerkat and VLA to cross-match the Herschel sources with the SDSS quasar catalogue. Our sample spans over a wide range of redshifts ($0
Speaker: Ismail Eissa (University of Groningen)
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Session: ClosingConvener: Roberto Pizzo
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ClosingSpeaker: Roberto Pizzo
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