Showing 1–50 of 67 results for author: Mingo, B

Radio Galaxies and Jet Duty Cycles

Authors: M. J. Hardcastle, C. Konar, S. Dutta, D. V. Lal, R. D. Baldi, M. Brienza, A. Hota, M. Kunert-Bajraszewska, B. Mingo, M. Pandey-Pommier, K. Rubinur, S. Shabala, E. Vardoulaki

Abstract: Radio-luminous active galactic nuclei, or radio galaxies, are the brightest population of objects in the extragalactic radio sky and will be seen in large numbers in essentially every SKA observation. Despite having been studied for more than seventy years, some aspects of radio galaxy physics are still poorly understood, and the SKA will shed light on this by enabling the generation of very large… ▽ More Radio-luminous active galactic nuclei, or radio galaxies, are the brightest population of objects in the extragalactic radio sky and will be seen in large numbers in essentially every SKA observation. Despite having been studied for more than seventy years, some aspects of radio galaxy physics are still poorly understood, and the SKA will shed light on this by enabling the generation of very large samples of high-resolution, sensitive, broad-band images of radio galaxies, allowing us to probe, for example, regions of particle acceleration, spectral ageing, and the magnetic field structures both internal and external to the radio lobes. A key feature of the radio galaxy population is that observations of extended sources probe the past history, and thus the duty cycles, of accretion onto the central supermassive black hole, and we discuss ways in which the SKA will improve our understanding of episodic and dying radio galaxies in particular.} △ Less

Submitted 27 June, 2026; originally announced June 2026.

Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no: AASKAII/Hardcastle01

Report number: AASKAII/Hardcastle01

The Emerging Population of High-energy Emitting Radio Galaxies

Authors: G. Bruni, V. S. Paliya, D. J. Saikia, L. Bassani, R. D. Baldi, E. Bronzini, F. D'Ammando, S. del Palacio, M. Kadler, Y. Y. Kovalev, D. V. Lal, G. Migliori, B. Mingo, J. Moldon, L. Ostorero, F. Panessa, M. Persic, I. Prandoni, L. Ricci, T. Savolainen, F. Shankar, F. Tavecchio, E. Traianou, F. Ubertosi, T. Venturi

Abstract: High-energy emission from radio galaxies provides a unique laboratory to study the connection between accretion, jet formation, and particle acceleration in active galactic nuclei (AGN). The recent detection of $γ$-ray emission from misaligned radio galaxies - including Compact Symmetric Objects (CSOs), FR0, FRI/II, and even Giant Radio Galaxies (GRGs) - has shown that efficient particle accelerat… ▽ More High-energy emission from radio galaxies provides a unique laboratory to study the connection between accretion, jet formation, and particle acceleration in active galactic nuclei (AGN). The recent detection of $γ$-ray emission from misaligned radio galaxies - including Compact Symmetric Objects (CSOs), FR0, FRI/II, and even Giant Radio Galaxies (GRGs) - has shown that efficient particle acceleration is not limited to blazars, but occurs throughout the full radio-loud AGN population. This finding supports a unifying framework where leptonic synchrotron, synchrotron self-Compton (SSC), and external inverse-Compton (EIC) processes coexist across multiple spatial scales, from the inner jet and corona to the extended lobes, possibly with a hadronic contribution in dense environments. The Square Kilometre Array (SKA) will be pivotal in advancing this field. SKA1-Low will detect and characterize diffuse, low-surface-brightness emission tracing aged plasma and jet duty cycles. SKA1-Mid will enable high-resolution spectral and polarimetric studies of compact jets and nuclear regions, while SKA-VLBI will connect parsec- to kiloparsec-scale structures, identifying the exact sites of high-energy dissipation. In synergy with forthcoming high-energy missions such as NewAthena and CTAO, SKA will provide the first spatially resolved, multi-scale view of particle acceleration and energy release in misaligned AGN, unveiling the physical link between the central engine and its large-scale feedback on the host galaxy evolution. △ Less

Submitted 25 June, 2026; originally announced June 2026.

Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no: AASKAII/Bruni01. Advancing Astrophysics with the SKA II (AASKAII) outlines the transformative scientific advances that will be enabled by the SKA telescopes

Report number: AASKAII/Bruni01

Evolution of AGN Across Cosmic Epochs with the SKAO

Authors: R. Kondapally, V. Singh, G. Mazzolari, I. Delvecchio, A. Datta, A. Kayal, B. Mingo, J. Moldon, J. Petley, I. Prandoni, K. Rubinur, S. Shabala, F. Shankar

Abstract: Understanding the evolution of active galactic nuclei (AGN) and their host galaxies across cosmic epochs is one of the key science drivers of extragalactic astronomy. The detection of AGN residing in dusty environments and at high redshifts is difficult due to obscuration and faintness which poses a challenge in understanding AGN evolution across cosmic time. Deep radio continuum surveys (rms nois… ▽ More Understanding the evolution of active galactic nuclei (AGN) and their host galaxies across cosmic epochs is one of the key science drivers of extragalactic astronomy. The detection of AGN residing in dusty environments and at high redshifts is difficult due to obscuration and faintness which poses a challenge in understanding AGN evolution across cosmic time. Deep radio continuum surveys (rms noise $<$ 1 $μ$Jy~beam$^{-1}$) from the Square Kilometre Array Observatory (SKAO) will be an efficient means to detect and study a broad population of AGN across cosmic history. In this chapter, we present radio luminosity functions, source counts, and detection rates of AGN based on the SKAO simulated radio source catalogues. We demonstrate that the SKA-Mid multi-tiered surveys, in particular, reaching sub-$μ$Jy depths, will allow us to characterise the bulk of the radio-AGN complete down to $L_{\rm{1.4\,GHz}} \sim 10^{23}\,\rm{W\,Hz^{-1}}$ and enable us to probe the evolution of radio-AGN across a wide range of luminosities and all galaxy environments up to $z \sim 6$. Overall, our work highlights the importance of deep multi-tiered SKAO radio continuum surveys for studying the evolution of radio-AGN activity across cosmic time. △ Less

Submitted 23 June, 2026; originally announced June 2026.

Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Kondapally01

Report number: AASKAII/Kondapally01

Probing the environments of FRI and FRII radio galaxies in LoTSS DR2 with galaxy clusters

Authors: Tong Pan, Yuming Fu, H. J. A. Rottgering, J. M. G. H. J. de Jong, M. J. Hardcastle, B. Mingo, L. Clews, M. Magliocchetti, J. W. Petley, Bohan Yue

Abstract: The origin of the Fanaroff--Riley Class I/II (FRI/FRII) morphological dichotomy remains uncertain. We investigate whether cluster-scale environment contributes to this distinction using a morphologically classified LoTSS DR2 catalogue at \(z<0.4\). We construct a volume-limited sample with \(L_{144}>4\times10^{24}\,\mathrm{W\,Hz^{-1}}\) and a luminosity--redshift paired sample, and cross-match the… ▽ More The origin of the Fanaroff--Riley Class I/II (FRI/FRII) morphological dichotomy remains uncertain. We investigate whether cluster-scale environment contributes to this distinction using a morphologically classified LoTSS DR2 catalogue at \(z<0.4\). We construct a volume-limited sample with \(L_{144}>4\times10^{24}\,\mathrm{W\,Hz^{-1}}\) and a luminosity--redshift paired sample, and cross-match them with DESI Legacy Imaging Survey galaxy clusters. A radio galaxy is associated with a cluster if \(|Δz|<0.01\), projected separation \(<2R_{500}\). In the volume-limited sample, \(48.6\%\) of FRIs and \(30.6\%\) of FRIIs are cluster-associated; in the paired sample, the corresponding fractions are \(45.6\%\) and \(32.6\%\). The difference is stronger at \(L_{144}>10^{26}\,\mathrm{W\,Hz^{-1}}\), where the fractions are \(55.6\%\) versus \(19.0\%\) in the volume-limited sample and \(50.0\%\) versus \(6.7\%\) in the paired sample. However, cluster-associated FRIs and FRIIs occupy similar environments: their radio luminosities and stellar masses show similar trends with cluster richness and \(M_{500}\), and their radial distributions both peak near \(0.5R_{500}\) and decline beyond \(R_{500}\). Most cluster-associated sources are brightest cluster galaxies (BCGs), with fractions of \(74.8\%\) for FRIs and \(61.9\%\) for FRIIs in the volume-limited sample, and \(78.1\%\) and \(65.9\%\) in the paired sample. These results show that FRIIs are less frequently found in clusters, especially at high radio luminosity, consistent with dense intracluster gas disrupting or decelerating jets and suppressing stable FRII structures. Nevertheless, once inside clusters, FRIs and FRIIs inhabit similar large-scale environments, implying that cluster-scale properties alone are unlikely to be the primary driver of the FRI/FRII dichotomy. △ Less

Submitted 22 May, 2026; originally announced May 2026.

Comments: 12 pages, 13 figures, 3 tables. Accepted for publication by A&A

The diverse morphologies and evolution of low-luminosity edge-brightened radio galaxies

Authors: B. Barkus, J. H. Croston, B. Mingo, M. J. Hardcastle, G. Gürkan, V. H. Mahatma

Abstract: Fanaroff-Riley class I (FRI) radio galaxies show centre-brightened emission from disrupted lower power jets, while traditionally more luminous class II (FRIIs), are edge-brightened, with relativistic jets terminating in hotspots. Population studies of radio-loud AGN (RLAGN) with low frequency, deep, wide-field surveys have revealed FRII-like radio structures at lower luminosities. We present the f… ▽ More Fanaroff-Riley class I (FRI) radio galaxies show centre-brightened emission from disrupted lower power jets, while traditionally more luminous class II (FRIIs), are edge-brightened, with relativistic jets terminating in hotspots. Population studies of radio-loud AGN (RLAGN) with low frequency, deep, wide-field surveys have revealed FRII-like radio structures at lower luminosities. We present the first high-resolution morphological investigation of a representative LOFAR-selected sample of low-luminosity FRIIs, to determine whether this new population is physically distinct from traditional high-luminosity FRIIs. Using new $1.5$-GHz Jansky Very Large Array (VLA) observations for a sample of 19 low-luminosity FRIIs, from the LOFAR Two Metre Sky Survey Data Release 1 (LoTSS DR1), with luminosities up to three orders of magnitude lower than the typical FR break ($L_{150} = 10^{26}$ W Hz$^{-1}$). We examine the compact features and perform spectral index analysis to identify hotspots, cores and signatures of restarting or remnant activity. We find a higher prevalence of cores and a comparable number of hotspots in the low-luminosity FRII sample compared to a randomly-selected sample of luminous ($L_{150}>10^{26}$ W Hz$^{-1}$) FRIIs selected from the same parent LOFAR sample. Approximately 32 per cent of low-luminosity FRIIs show restarting or remnant behaviour, while $\sim 32$ per cent are active FRIIs with compact hotspots. Our results show that FRII source dynamics occur at low radio luminosities, but reinforce earlier conclusions that the population of low-luminosity edge-brightened RLAGN is highly diverse. Binary morphological classifications should be used cautiously as a first step towards more nuanced investigations of the complexity of jet life cycles and evolution. △ Less

Submitted 8 May, 2026; originally announced May 2026.

Comments: 16 pages, 7 figures, 8 tables. Accepted for publication in MNRAS

The LOFAR Two-metre Sky Survey: VII. Third Data Release

Authors: T. W. Shimwell, M. J. Hardcastle, C. Tasse, A. Drabent, A. Botteon, W. L. Williams, P. N. Best, H. J. A. Röttgering, M. Brüggen, G. Brunetti, J. R. Callingham, K. T. Chyży, J. E. Conway, F. De Gasperin, M. Haverkorn, C. Horellou, N. Jackson, G. K. Miley, L. K. Morabito, R. Morganti, S. P. O'Sullivan, D. J. Schwarz, D. J. B. Smith, R. J. van Weeren, H. K. Vedantham , et al. (77 additional authors not shown)

Abstract: We present the third data release of the LOFAR Two-metre Sky Survey (LoTSS-DR3). The survey images cover 88% of the northern sky and were created from 12,950 hrs of data (18.6 PB) accumulated over 10.5 years. The images were produced through direction-independent and direction-dependent calibration pipelines that correct for instrumental effects as well as spatially and temporally varying ionosphe… ▽ More We present the third data release of the LOFAR Two-metre Sky Survey (LoTSS-DR3). The survey images cover 88% of the northern sky and were created from 12,950 hrs of data (18.6 PB) accumulated over 10.5 years. The images were produced through direction-independent and direction-dependent calibration pipelines that correct for instrumental effects as well as spatially and temporally varying ionospheric distortions. In our 120-168 MHz continuum mosaic images with an angular resolution of 6 arcsec (9 arcsec below declination 10$^\circ$) we catalogue 13,667,877 sources, formed from 16,943,656 Gaussian components. The scatter in the astrometric precision approximately follows the expected noise-like behaviour but with an additional systematic component of at least 0.24 arcsec that is likely due to calibration imperfections. The random flux density scale error is 6%, while the systematic offset was previously shown to be within 2%. The median sensitivity of our mosaics is 92$μ$Jy beam$^{-1}$. Completeness simulations, accounting for realistic source models, time- and bandwidth-smearing effects, and astrometric errors, indicate that we detect more than 95% of compact sources with integrated flux densities exceeding 9 times the local root mean square (RMS) noise. However, the recovered source counts in a particular integrated flux density bin do not match the injected counts until flux densities exceed 45 times the local RMS noise. The Euclidean-normalised differential source counts derived from the survey constrain the radio source population over five orders of magnitude and are in good agreement with previous deep and wide-area surveys. All data products are publicly available, including catalogues, individual-field Stokes I, Q, U, and V images, mosaicked Stokes I images, and $uv$ data with associated direction-dependent calibration solutions. △ Less

Submitted 17 February, 2026; originally announced February 2026.

Comments: 15 figures, 2 tables and 22 pages. The catalogues, images and uv-data associated with this data release are publicly available via https://lofar-surveys.org/

Simulating the Formation of the Young "Fermi Bubbles" in the Circinus Galaxy

Authors: Shaokun Xie, Fulai Guo, Ruiyu Zhang, B. Mingo, Fangzheng Shi, Jiang-Tao Li

Abstract: The Fermi and eROSITA bubbles in the Milky Way represent an archetypal case of galactic nucleus feedback, yet their origin remains highly debated. Here we use hydrodynamic simulations to investigate the formation of the "Fermi bubbles" in the nearby Circinus galaxy, a pair of kpc-scaled elliptical bubbles seen in both radio and X-ray observations. We find that a pair of active galactic nucleus (AG… ▽ More The Fermi and eROSITA bubbles in the Milky Way represent an archetypal case of galactic nucleus feedback, yet their origin remains highly debated. Here we use hydrodynamic simulations to investigate the formation of the "Fermi bubbles" in the nearby Circinus galaxy, a pair of kpc-scaled elliptical bubbles seen in both radio and X-ray observations. We find that a pair of active galactic nucleus (AGN) jets drive forward shocks in the circumgalactic medium, and after evolving for ~0.95 Myr, the shock-delineated bubble pair roughly matches the observed Circinus bubbles in size and morphology. Our mock X-ray image and spectrum reproduce the observed edge-brightened X-ray surface brightness distribution and spectrum quite well, and suggest that non-thermal emissions from the jet ejecta also contribute substantially to radio and X-ray emissions from the inner "hotspot" region. We further show that AGN winds tend to produce more spherical bubbles with a wider base near the galactic plane, inconsistent with observations. The hotspot emissions and the misalignment between the galaxy rotational axis and the bubble's axis argue against a starburst wind origin. Our study thus corroborates the AGN jet-shock model for the origin of both the Circinus bubbles and the Fermi bubbles, and suggests that AGN jet feedback may be a common origin of extended gaseous bubbles in regular disk galaxies, potentially playing an important role in their evolution. △ Less

Submitted 7 January, 2026; originally announced January 2026.

Comments: Submitted to ApJ; 14 pages, 9 figures

Radio-loud AGN morphology and host-galaxy properties in the LOFAR Two-Metre Sky Survey Data Release 2

Authors: L. Clews, J. H. Croston, H. Dickinson, B. Mingo, M. J. Hardcastle, B. Barkus, J. M. G. H. J. de Jong, H. J. A. Röttgering

Abstract: Radio-loud active galaxies (RLAGN) can exhibit various morphologies. The Fanaroff-Riley (FR) classifications, which are defined by the locations of peaks in surface brightness, have been applied to many catalogues of RLAGN. The FR classifications were initially found to correlate with radio luminosity. However, recent surveys have demonstrated that radio luminosity alone does not reliably predict… ▽ More Radio-loud active galaxies (RLAGN) can exhibit various morphologies. The Fanaroff-Riley (FR) classifications, which are defined by the locations of peaks in surface brightness, have been applied to many catalogues of RLAGN. The FR classifications were initially found to correlate with radio luminosity. However, recent surveys have demonstrated that radio luminosity alone does not reliably predict radio morphology. We have devised a new-semi automated method involving ridgeline characterisations to compile the largest known classified catalogue of RLAGN to date with data from the second data release of the LOFAR Two-Metre Sky Survey (LoTSS DR2). We reassess the FR divide and its cause by examining the physical and host galaxy properties of $3590$ FRIIs and $2354$ FRIs (at $z \leq 0.8$). We find that RLAGN near the FR divide with $10^{25} \le L_{144} \le 10^{26} $ WHz$^{-1}$ are more likely to show FRI over FRII morphology if they occupy more massive host galaxies. We find no correlation, when considering selection effects, between the FR break luminosity and stellar mass or host-galaxy rest-frame absolute magnitude. Overall, we find the cause of different radio morphologies in this sample to be complex. Considering sources near the FR divide with $10^{25} \le L_{144} \le 10^{26} $ WHz$^{-1}$, we find evidence to support inner environment having a role in determining jet disruption. We make available a public catalogue of morphologies for our sample, which will be of use for future investigations of RLAGN and their impact on their surroundings. △ Less

Submitted 10 June, 2025; originally announced June 2025.

Comments: 17 pages 11 figures

Radio AGN selection in LoTSS DR2

Authors: M. J. Hardcastle, J. C. S. Pierce, K. J. Duncan, G. Gürkan, Y. Gong, M. A. Horton, B. Mingo, H. J. A. Röttgering, D. J. B. Smith

Abstract: The wide-area component of the LOFAR Two-Metre Sky Survey (LoTSS) is currently the largest radio survey ever carried out, and a large fraction of the 4.5 million radio sources it contains have been optically identified with galaxies or quasars with spectroscopic or photometric redshifts. Identification of radio-luminous AGN from this LoTSS source catalogue is not only important from the point of v… ▽ More The wide-area component of the LOFAR Two-Metre Sky Survey (LoTSS) is currently the largest radio survey ever carried out, and a large fraction of the 4.5 million radio sources it contains have been optically identified with galaxies or quasars with spectroscopic or photometric redshifts. Identification of radio-luminous AGN from this LoTSS source catalogue is not only important from the point of view of understanding the accretion history of the universe, but also enables a wide range of other science. However, at present the vast majority of the optical identifications lack spectroscopic information or well-sampled spectral energy distributions. We show that colour and absolute magnitude information from the Wide-Field Infrared Survey Explorer (WISE) allows for the robust and efficient selection of radio AGN candidates, generating a radio AGN candidate sample of around 600,000 objects with flux density $> 1.1$ mJy, spanning 144-MHz luminosities between $10^{21}$ and $10^{29}$ W Hz$^{-1}$. We use the catalogue to constrain the total sky density of radio-luminous AGN and the evolution of their luminosity function between $z=0$ and $z\approx 1$, and show that the typical mass of their host galaxies, around $10^{11} M_\odot$, is essentially independent of radio luminosity above around $L_{144} \approx 10^{24}$ W Hz$^{-1}$. Combining with Very Large Array Sky Survey (VLASS) data, we show that the core prominences, radio spectral indices and variability of extended sources from the sample are qualitatively consistent with the expectations from unified models. A catalogue of the radio AGN candidates is released with this paper. △ Less

Submitted 12 April, 2025; originally announced April 2025.

Comments: 23 pages, accepted for publication in MNRAS

Radio-AGN activity across the galaxy population: dependence on stellar mass, star-formation rate, and redshift

Authors: R. Kondapally, P. N. Best, K. J. Duncan, H. J. A. Röttgering, D. J. B. Smith, I. Prandoni, M. J. Hardcastle, T. Holc, A. L. Patrick, M. I. Arnaudova, B. Mingo, R. K. Cochrane, S. Das, P. Haskell, M. Magliocchetti, K. Małek, G. K. Miley, C. Tasse, W. L. Williams

Abstract: We characterise the co-evolution of radio-loud AGN and their galaxies by mapping the dependence of radio-loud AGN activity on stellar mass and star-formation rate (SFR) across cosmic time (out to $z \sim 1.5$). Deep LOFAR radio observations are combined with large galaxy samples to study the incidence of radio-loud AGN across the galaxy population; the AGN are further split into low-excitation rad… ▽ More We characterise the co-evolution of radio-loud AGN and their galaxies by mapping the dependence of radio-loud AGN activity on stellar mass and star-formation rate (SFR) across cosmic time (out to $z \sim 1.5$). Deep LOFAR radio observations are combined with large galaxy samples to study the incidence of radio-loud AGN across the galaxy population; the AGN are further split into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs). We find that LERG activity occurs over a wide range of SFRs, whereas HERGs are typically found in galaxies with ongoing star formation. The LERGs are then split based on their SFRs relative to the main sequence, across redshift. Within quiescent galaxies, LERG activity shows a steep stellar mass dependence with the same normalisation across the past $\sim$ 10 Gyr; this indicates that hot gas fuels LERGs in quiescent galaxies across cosmic time. In massive galaxies ($\log_{10}(M/\rm{M_{\odot}}) \gtrsim 11$), the incidence of LERGs is roughly constant across the galaxy population, suggesting that LERGs in massive galaxies may be fuelled by hot gas regardless of the star-formation activity. At lower masses, however, LERG activity is significantly more enhanced (by a factor of up to 10) in star-forming galaxies compared to quiescent galaxies; this suggests that an additional fuelling mechanism, likely associated with cold gas, may fuel the LERGs in galaxies with higher SFRs. We find that HERGs typically accrete above 1 per cent of the Eddington-scaled accretion rate, and the LERGs typically accrete below this level. △ Less

Submitted 12 November, 2024; originally announced November 2024.

Comments: Accepted for publication in MNRAS, 18 pages, 10 figures

The NuSTAR Local AGN $N_{\rm H}$ Distribution Survey (NuLANDS) I: Towards a Truly Representative Column Density Distribution in the Local Universe

Authors: Peter G. Boorman, Poshak Gandhi, Johannes Buchner, Daniel Stern, Claudio Ricci, Mislav Baloković, Daniel Asmus, Fiona A. Harrison, Jiří Svoboda, Claire Greenwell, Michael Koss, David M. Alexander, Adlyka Annuar, Franz Bauer, William N. Brandt, Murray Brightman, Francesca Panessa, Chien-Ting J. Chen, Duncan Farrah, Karl Forster, Brian Grefenstette, Sebastian F. Hönig, Adam B. Hill, Elias Kammoun, George Lansbury , et al. (11 additional authors not shown)

Abstract: Hard X-ray-selected samples of Active Galactic Nuclei (AGN) provide one of the cleanest views of supermassive black hole accretion, but are biased against objects obscured by Compton-thick gas column densities of $N_{\rm H}$ $>$ 10$^{24}$ cm$^{-2}$. To tackle this issue, we present the NuSTAR Local AGN $N_{\rm H}$ Distribution Survey (NuLANDS)$-$a legacy sample of 122 nearby ($z$ $<$ 0.044) AGN pr… ▽ More Hard X-ray-selected samples of Active Galactic Nuclei (AGN) provide one of the cleanest views of supermassive black hole accretion, but are biased against objects obscured by Compton-thick gas column densities of $N_{\rm H}$ $>$ 10$^{24}$ cm$^{-2}$. To tackle this issue, we present the NuSTAR Local AGN $N_{\rm H}$ Distribution Survey (NuLANDS)$-$a legacy sample of 122 nearby ($z$ $<$ 0.044) AGN primarily selected to have warm infrared colors from IRAS between 25$-$60 $μ$m. We show that optically classified type 1 and 2 AGN in NuLANDS are indistinguishable in terms of optical [OIII] line flux and mid-to-far infrared AGN continuum bolometric indicators, as expected from an isotropically selected AGN sample, while type 2 AGN are deficient in terms of their observed hard X-ray flux. By testing many X-ray spectroscopic models, we show the measured line-of-sight column density varies on average by $\sim$ 1.4 orders of magnitude depending on the obscurer geometry. To circumvent such issues we propagate the uncertainties per source into the parent column density distribution, finding a directly measured Compton-thick fraction of 35 $\pm$ 9%. By construction, our sample will miss sources affected by severe narrow-line reddening, and thus segregates sources dominated by small-scale nuclear obscuration from large-scale host-galaxy obscuration. This bias implies an even higher intrinsic obscured AGN fraction may be possible, although tests for additional biases arising from our infrared selection find no strong effects on the measured column-density distribution. NuLANDS thus holds potential as an optimized sample for future follow-up with current and next-generation instruments aiming to study the local AGN population in an isotropic manner. △ Less

Submitted 9 October, 2024; originally announced October 2024.

Comments: Accepted for publication in ApJ. 50 pages (78 including appendix and bibliography), 21 figures

Core prominence as a signature of restarted jet activity in the LOFAR radio-galaxy population

Authors: Dhanya G. Nair, Raffaella Morganti, Marisa Brienza, Beatriz Mingo, Judith H. Croston, Nika Jurlin, Timothy W. Shimwell, Joseph R. Callingham, Martin J. Hardcastle

Abstract: (abridged) Characterizing duty cycles of recurrent phases of dormancy and activity in supermassive black holes in active galactic nuclei is crucial in understanding impact of energy released on host galaxies and their evolution. However, identifying sources in quiescent and restarted phases is challenging. Our goal is to identify and characterize a substantial sample of radio galaxies in restarted… ▽ More (abridged) Characterizing duty cycles of recurrent phases of dormancy and activity in supermassive black holes in active galactic nuclei is crucial in understanding impact of energy released on host galaxies and their evolution. However, identifying sources in quiescent and restarted phases is challenging. Our goal is to identify and characterize a substantial sample of radio galaxies in restarted phase and explore core prominence as a signature of this activity. We expand our prior study from a $30\,\mathrm{deg^2}$ area in Lockman Hole to a larger $424\,\mathrm{deg^2}$ region in Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) field using visually selected core-dominated radio galaxies. We used 144 MHz LOFAR survey images to identify galaxies with restarting jets. By applying selection criteria, including radio core dominance, low surface brightness extended emission, spectral index properties, and morphology, we found 69 candidate restarted radio galaxies. These candidates show diverse intrinsic morphology, spanning FRI, FRII, core-with-halo, and asymmetric forms, suggesting different progenitors. Among these, nine galaxies exhibit ultra-steep spectrum extended emission combined with high radio core prominence, representing previous and current epochs of jet activity. This subset supports a model where the switch-on and switch-off mechanism occurs with fast duty cycle. The restarted candidates span radio luminosities from log$_{10}$(L$_\mathrm{144 MHz}$/$\mathrm{WHz^{-1}}$) = 23.24 to 26.80, with sizes between 88 and 1659 kpc, including 16 giant radio galaxies. Their total stellar content aligns with massive elliptical galaxies. Our findings at $z<0.4$ suggest that many restarting galaxies are not found in rich cluster environments, consistent with broader radio-galaxy population. This study confirms core prominence as an effective parameter for selecting restarted radio sources. △ Less

Submitted 23 September, 2024; originally announced September 2024.

Comments: 28 pages, 18 figures, 7 tables, accepted for publication in A&A

Journal ref: A&A 691, A287 (2024)

Radio properties of Green Pea galaxies

Authors: Abhijeet Borkar, Romana Grossová, Jiří Svoboda, Emily Moravec, Konstantinos Kouroumpatzakis, Peter G. Boorman, Barbora Adamcová, Beatriz Mingo, Matthias Ehle

Abstract: Green Peas (GPs) are young, compact, star-forming dwarf galaxies, and local (z~0.3) analogues of the early galaxies (z>6) considered to be mainly responsible for the reionisation of the Universe. Recent X-ray observations of GPs have detected high excess emission which cannot be accounted for by star formation alone, and implies presence of an active galactic nucleus (AGN). We employ radio observa… ▽ More Green Peas (GPs) are young, compact, star-forming dwarf galaxies, and local (z~0.3) analogues of the early galaxies (z>6) considered to be mainly responsible for the reionisation of the Universe. Recent X-ray observations of GPs have detected high excess emission which cannot be accounted for by star formation alone, and implies presence of an active galactic nucleus (AGN). We employ radio observations to study the radio properties of GPs, build their radio spectral energy distributions, and verify the presence of AGNs. We performed new radio observations of three GPs with the Karl G. Jansky Very Large Array (JVLA) in the L, C, and X bands (1.4, 6 and 10 GHz resp.), supplemented by the data from archival observations and large radio surveys. We also analysed the archival radio data for a larger sample of GPs and blueberry (BBs) galaxies, which are lower-mass and lower-redshift analogues of the GPs. To understand the significance of the radio observations, we assess the detectability of these sources, and compare the detected radio luminosities with the expectations from theoretical and empirical relations. Two of the three targeted GPs were strongly detected ($>10σ$) in the JVLA observations and their fluxes are consistent with star formation, while the third source was undetected. Although a large fraction (~75%) of the sources from the larger archival sample of GPs and BBs could be detected with archival surveys, only a small number (<40%) are detected and their radio luminosity is significantly lower than the expectation from empirical relations. Our results show that the majority of the dwarf galaxy sample is highly underluminous. Especially towards the lower end of galaxy mass and star formation rate (SFR), the radio luminosity-SFR relation deviates from the empirical relations, suggesting that the relations established for larger galaxies may not hold towards the low-mass end. △ Less

Submitted 28 March, 2024; originally announced March 2024.

Comments: 9 pages, 4 figures, accepted for publication to A&A

Journal ref: A&A 687, A137 (2024)

The nature of compact radio-loud AGN: a systematic look at the LOFAR AGN population

Authors: J. Chilufya, M. J. Hardcastle, J. C. S. Pierce, J. H. Croston, B. Mingo, X. Zheng, R. D. Baldi, H. J. A. Röttgering

Abstract: We investigate the nature of low-luminosity radio-loud active galactic nuclei (RLAGN) selected from the LOFAR Two-metre Sky Survey (LoTSS) first data release (DR1). Using optical, mid-infrared, and radio data, we have conservatively selected 55 radiative AGN candidates from DR1 within the redshift range $0.03<z<0.1$. We show using high-frequency {\it Karl G. Jansky} Very Large Array (VLA) observat… ▽ More We investigate the nature of low-luminosity radio-loud active galactic nuclei (RLAGN) selected from the LOFAR Two-metre Sky Survey (LoTSS) first data release (DR1). Using optical, mid-infrared, and radio data, we have conservatively selected 55 radiative AGN candidates from DR1 within the redshift range $0.03<z<0.1$. We show using high-frequency {\it Karl G. Jansky} Very Large Array (VLA) observations that 10 out of 55 objects show radio emission on scales $>$$1-3$ kpc, 42 are compact at the limiting resolution of 0.35 arcsec (taking an upper limit on the projected physical size, this corresponds to less than 1 kpc), and three are undetected. The extended objects display a wide range of radio morphologies: two-jet (5), one-jet (4), and double-lobed (1). We present the radio spectra of all detected radio sources which range from steep to flat/inverted and span the range seen for other compact radio sources such as compact symmetric objects (CSOs), compact steep spectrum (CSS) sources, and gigahertz peaked-spectrum (GPS) sources. Assuming synchrotron self-absorption (SSA) for flat/inverted radio spectrum sources, we predict small physical sizes for compact objects to range between $2-53$ pc. Alternatively, using free-free absorption (FFA) models, we have estimated the free electron column depth for all compact objects, assuming a homogeneous absorber. We find that these objects do not occupy a special position on the power/linear size ($P-D$) diagram but some share a region with radio-quiet quasars (RQQs) and so-called `FR0' sources in terms of radio luminosity and linear size. △ Less

Submitted 29 February, 2024; originally announced February 2024.

Comments: Accepted for publication in the Monthly Notices of the Royal Astronomy Society (MNRAS) journal

Cosmic evolution of FRI and FRII sources out to z=2.5

Authors: J. M. G. H. J. de Jong, H. J. A. Röttgering, R. Kondapally, B. Mingo, R. J. van Weeren, P. N. Best, L. K. Morabito, M. Magliocchetti, J. B. R. Oonk, A. Villarrubia-Aguilar, F. F. Vecchi

Abstract: Radio-loud active galactic nuclei (RLAGN) play an important role in the evolution of galaxies through the effects on their environment. The two major morphological classes are core-bright (FRI) and edge-bright (FRII) sources. With the LOw-Frequency ARray (LOFAR) we compare the FRI and FRII evolution down to lower flux densities and with larger samples than before with the aim to examine the cosmic… ▽ More Radio-loud active galactic nuclei (RLAGN) play an important role in the evolution of galaxies through the effects on their environment. The two major morphological classes are core-bright (FRI) and edge-bright (FRII) sources. With the LOw-Frequency ARray (LOFAR) we compare the FRI and FRII evolution down to lower flux densities and with larger samples than before with the aim to examine the cosmic space density evolution for FRIs and FRIIs by analyzing their space density evolution between L_150~10^24.5 W/Hz and L_150~10^28.5 W/Hz and up to z=2.5. We construct radio luminosity functions (RLFs) from FRI and FRII catalogues based on recent data from LOFAR at 150MHz to study the space densities as a function of radio luminosity and redshift. To partly correct for selection biases and completeness, we simulate how sources appear at a range of redshifts. We report a space density enhancement from low to high redshift for FRI and FRII sources brighter than L_150~10^27 W/Hz. This is possibly related to the higher gas availability in the earlier denser universe. The constant FRI/FRII space density ratio evolution as a function of radio luminosity and redshift in our results suggests that the jet-disruption of FRIs might be primarily caused by events occurring on scales within the host galaxy, rather than being driven by changes in the overall large-scale environment. Remaining selection biases in our results also highlight the need to resolve more sources at angular scales below 40 arcsec and therefore strengthens the motivation for the further development and automation of the calibration and imaging pipeline of LOFAR data to produce images at sub-arcsecond resolution. △ Less

Submitted 22 November, 2023; originally announced November 2023.

The Multi-Wavelength Environment of Second Bologna Catalog Sources

Authors: A. Paggi, F. Massaro, H. Peña-Herazo, V. Missaglia, A. Jimenez-Gallardo, F. Ricci, S. Ettori, G. Giovannini, F. Govoni, R. D. Baldi, B. Mingo, M. Murgia, E. Liuzzo, F. Galati

Abstract: We present the first results of the Chandra Cool Targets (CCT) survey of the Second Bologna Catalog (B2CAT) of powerful radio sources, aimed at investigating the extended X-ray emission surrounding these sources. For the first 33 sources observed in the B2CAT CCT survey, we performed both imaging and spectral X-ray analysis, producing multi-band Chandra images, and compared them with radio observa… ▽ More We present the first results of the Chandra Cool Targets (CCT) survey of the Second Bologna Catalog (B2CAT) of powerful radio sources, aimed at investigating the extended X-ray emission surrounding these sources. For the first 33 sources observed in the B2CAT CCT survey, we performed both imaging and spectral X-ray analysis, producing multi-band Chandra images, and compared them with radio observations. To evaluate the presence of extended emission in the X-rays, we extracted surface flux profiles comparing them with simulated ACIS Point Spread Functions. We detected X-ray nuclear emission for 28 sources. In addition, we detected 8 regions of increased X-ray flux originating from radio hot-spots or jet knots, and a region of decreased flux, possibly associated with an X-ray cavity. We performed X-ray spectral analysis for 15 nuclei and found intrinsic absorption significantly larger than the Galactic values in four of them. We detected significant extended X-ray emission in five sources, and fitted their spectra with thermal models with gas temperatures $\sim 2 \text{ keV}$. In the case of B2.1 0742+31, the surrounding hot gas is compatible with the ICM of low luminosity clusters of galaxies, while the X-ray diffuse emission surrounding the highly disturbed WAT B2.3 2254+35 features a luminosity similar to those of relatively bright galaxy groups, although its temperature is similar to those of low luminosity galaxy clusters. These results highlight the power of the low-frequency radio selection, combined with short Chandra snapshot observations, to investigate the properties of the X-ray emission from radio sources. △ Less

Submitted 5 July, 2023; originally announced July 2023.

Comments: 38 pages, 13 figures, 6 tables. Accepted for publication in The Astrophysical Journal Supplement Series

The LOFAR Two-metre Sky Survey Deep Fields Data Release 1: V. Survey description, source classifications and host galaxy properties

Authors: P. N. Best, R. Kondapally, W. L. Williams, R. K. Cochrane, K. J. Duncan, C. L. Hale, P. Haskell, K. Malek, I. McCheyne, D. J. B. Smith, L. Wang, A. Botteon, M. Bonato, M. Bondi, G. Calistro Rivera, F. Gao, G. Gurkan, M. J. Hardcastle, M. J. Jarvis, B. Mingo, H. Miraghaei, L. K. Morabito, D. Nisbet, I. Prandoni, H. J. A. Rottgering , et al. (4 additional authors not shown)

Abstract: Source classifications, stellar masses and star formation rates are presented for 80,000 radio sources from the first data release of the Low Frequency Array Two-metre Sky Survey (LoTSS) Deep Fields, which represents the widest deep radio survey ever undertaken. Using deep multi-wavelength data spanning from the ultraviolet to the far-infrared, spectral energy distribution (SED) fitting is carried… ▽ More Source classifications, stellar masses and star formation rates are presented for 80,000 radio sources from the first data release of the Low Frequency Array Two-metre Sky Survey (LoTSS) Deep Fields, which represents the widest deep radio survey ever undertaken. Using deep multi-wavelength data spanning from the ultraviolet to the far-infrared, spectral energy distribution (SED) fitting is carried out for all of the LoTSS-Deep host galaxies using four different SED codes, two of which include modelling of the contributions from an active galactic nucleus (AGN). Comparing the results of the four codes, galaxies that host a radiative AGN are identified, and an optimised consensus estimate of the stellar mass and star-formation rate for each galaxy is derived. Those galaxies with an excess of radio emission over that expected from star formation are then identified, and the LoTSS-Deep sources are divided into four classes: star-forming galaxies, radio-quiet AGN, and radio-loud high-excitation and low-excitation AGN. Ninety-five per cent of the sources can be reliably classified, of which more than two-thirds are star-forming galaxies, ranging from normal galaxies in the nearby Universe to highly-starbursting systems at z>4. Star-forming galaxies become the dominant population below 150-MHz flux densities of about 1 mJy, accounting for 90 per cent of sources at a 150-MHz flux density of 100 microJy. Radio-quiet AGN comprise around 10 per cent of the overall population. Results are compared against the predictions of the SKADS and T-RECS radio sky simulations, and improvements to the simulations are suggested. △ Less

Submitted 9 May, 2023; originally announced May 2023.

Comments: Accepted for publication in MNRAS. Catalogues available at www.lofar-surveys.org/deepfields.html. 27 pages

A Quick Look at the 3GHz Radio Sky. II. Hunting for DRAGNs in the VLA Sky Survey

Authors: Yjan A. Gordon, Lawrence Rudnick, Heinz Andernach, Leah K. Morabito, Christopher P. O'Dea, Kaylan-Marie Achong, Stefi A. Baum, Caryelis Bayona-Figueroa, Eric J. Hooper, Beatriz Mingo, Melissa E. Morris, Adrian N. Vantyghem

Abstract: Active Galactic Nuclei (AGN) can often be identified in radio images as two lobes, sometimes connected to a core by a radio jet. This multi-component morphology unfortunately creates difficulties for source-finders, leading to components that are a) separate parts of a wider whole, and b) offset from the multiwavelength cross identification of the host galaxy. In this work we define an algorithm,… ▽ More Active Galactic Nuclei (AGN) can often be identified in radio images as two lobes, sometimes connected to a core by a radio jet. This multi-component morphology unfortunately creates difficulties for source-finders, leading to components that are a) separate parts of a wider whole, and b) offset from the multiwavelength cross identification of the host galaxy. In this work we define an algorithm, \textsc{DRAGNhunter}, for identifying Double Radio Sources associated with Active Galactic Nuclei (DRAGNs) from component catalog data in the first epoch \textit{Quick Look} images of the high resolution ($\approx 3''$ beam size) Very Large Array Sky Survey (VLASS). We use \textsc{DRAGNhunter} to construct a catalog of $>17,000$ DRAGNs in VLASS for which contamination from spurious sources is estimated at $\approx 11\,\%$. A `high-fidelity' sample consisting of $90\,\%$ of our catalog is identified for which contamination is $<3\,\%$. Host galaxies are found for $\approx 13,000$ DRAGNs as well as for an additional $234,000$ single-component radio sources. Using these data we explore the properties of our DRAGNs, finding them to be typically consistent with Fanaroff-Riley class II sources and allowing us to report the discovery of $31$ new giant radio galaxies identified using VLASS. △ Less

Submitted 22 May, 2023; v1 submitted 22 March, 2023; originally announced March 2023.

Comments: Accepted for publication in ApJS. 33 pages, 25 figures, 6 tables. Minor textual changes with respect to previous version, One table added, two example tables removed. Catalog data will be available via https://cirada.ca/, https://vizier.cds.unistra.fr/viz-bin/VizieR and in the online version of the ApJS article

The LOFAR LBA Sky Survey II. First data release

Authors: F. de Gasperin, H. W. Edler, W. L. Williams, J. R. Callingham, B. Asabere, M. Bruggen, G. Brunetti, T. J. Dijkema, M. J. Hardcastle, M. Iacobelli, A. Offringa, M. J. Norden, H. J. A. Rottgering, T. Shimwell, R. J. van Weeren, C. Tasse, D. J. Bomans, A. Bonafede, A. Botteon, R. Cassano, K. T. Chyzy, V. Cuciti, K. L. Emig, M. Kadler, G. Miley , et al. (5 additional authors not shown)

Abstract: The Low Frequency Array (LOFAR) is the only existing radio interferometer able to observe at ultra-low frequencies (<100 MHz) with high resolution (<15") and high sensitivity (<1 mJy/beam). To exploit these capabilities, the LOFAR Surveys Key Science Project is using the LOFAR Low Band Antenna (LBA) to carry out a sensitive wide-area survey at 41-66 MHz named the LOFAR LBA Sky Survey (LoLSS). LoLS… ▽ More The Low Frequency Array (LOFAR) is the only existing radio interferometer able to observe at ultra-low frequencies (<100 MHz) with high resolution (<15") and high sensitivity (<1 mJy/beam). To exploit these capabilities, the LOFAR Surveys Key Science Project is using the LOFAR Low Band Antenna (LBA) to carry out a sensitive wide-area survey at 41-66 MHz named the LOFAR LBA Sky Survey (LoLSS). LoLSS is covering the whole northern sky above declination 24 deg with a resolution of 15" and a sensitivity of 1-2 mJy/beam (1 sigma) depending on declination, field properties, and observing conditions. Here we present the first data release. An automated pipeline was used to reduce the 95 fields included in this data release. The data reduction procedures developed for this project have general application and are currently being used to process LOFAR LBA interferometric observations. Compared to the preliminary release, direction-dependent errors have been corrected for during the calibration process. This results in a typical sensitivity of 1.55 mJy/beam at the target resolution of 15". The first data release of the LOFAR LBA Sky Survey covers 650 sqdeg in the HETDEX spring field. The resultant data products released to the community include mosaic images (I and V Stokes) of the region, and a catalogue of 42463 detected sources and related Gaussian components used to describe sources' morphologies. Separate catalogues for 6 in-band frequencies are also released. The first data release of LoLSS shows that, despite the influences of the ionosphere, LOFAR can conduct large-scale surveys in the frequency window 42-66 MHz with unprecedentedly high sensitivity and resolution. The data can be used to derive unique information on the low-frequency spectral properties of many thousands of sources with a wide range of applications in extragalactic and galactic astronomy. △ Less

Submitted 30 January, 2023; originally announced January 2023.

Comments: 20 pages, 22 figures, images and catalogues available at https://www.lofar-surveys.org/lolss.html

Journal ref: A&A 673, A165 (2023)

The Faraday Rotation Measure Grid of the LOFAR Two-metre Sky Survey: Data Release 2

Authors: S. P. O'Sullivan, T. W. Shimwell, M. J. Hardcastle, C. Tasse, G. Heald, E. Carretti, M. Brüggen, V. Vacca, C. Sobey, C. L. Van Eck, C. Horellou, R. Beck, M. Bilicki, S. Bourke, A. Botteon, J. H. Croston, A. Drabent, K. Duncan, V. Heesen, S. Ideguchi, M. Kirwan, L. Lawlor, B. Mingo, B. Nikiel-Wroczyński, J. Piotrowska , et al. (2 additional authors not shown)

Abstract: A Faraday rotation measure (RM) catalogue, or RM Grid, is a valuable resource for the study of cosmic magnetism. Using the second data release (DR2) from the LOFAR Two-metre Sky Survey (LoTSS), we have produced a catalogue of 2461 extragalactic high-precision RM values across 5720 deg$^{2}$ of sky (corresponding to a polarized source areal number density of $\sim$0.43 deg$^{-2}$). The linear polar… ▽ More A Faraday rotation measure (RM) catalogue, or RM Grid, is a valuable resource for the study of cosmic magnetism. Using the second data release (DR2) from the LOFAR Two-metre Sky Survey (LoTSS), we have produced a catalogue of 2461 extragalactic high-precision RM values across 5720 deg$^{2}$ of sky (corresponding to a polarized source areal number density of $\sim$0.43 deg$^{-2}$). The linear polarization and RM properties were derived using RM synthesis from the Stokes $Q$ and $U$ channel images at an angular resolution of 20'' across a frequency range of 120 to 168 MHz with a channel bandwidth of 97.6 kHz. The fraction of total intensity sources ($>1$ mJy beam$^{-1}$) found to be polarized was $\sim$0.2%. The median detection threshold was 0.6 mJy beam$^{-1}$ ($8σ_{QU}$), with a median RM uncertainty of 0.06 rad m$^{-2}$ (although a systematic uncertainty of up to 0.3 rad m$^{-2}$ is possible, after the ionosphere RM correction). The median degree of polarization of the detected sources is 1.8%, with a range of 0.05% to 31%. Comparisons with cm-wavelength RMs indicate minimal amounts of Faraday complexity in the LoTSS detections, making them ideal sources for RM Grid studies. Host galaxy identifications were obtained for 88% of the sources, along with redshifts for 79% (both photometric and spectroscopic), with the median redshift being 0.6. The focus of the current catalogue was on reliability rather than completeness, and we expect future versions of the LoTSS RM Grid to have a higher areal number density. In addition, 25 pulsars were identified, mainly through their high degrees of linear polarization. △ Less

Submitted 18 January, 2023; originally announced January 2023.

Comments: 20 pages, 23 figures, 3 tables. Accepted for publication in MNRAS. Go to https://lofar-mksp.org/data/ to download the catalogue and associated data products

V-LoTSS: The Circularly-Polarised LOFAR Two-metre Sky Survey

Authors: J. R. Callingham, T. W. Shimwell, H. K. Vedantham, C. G. Bassa, S. P. O'Sullivan, T. W. H. Yiu, S. Bloot, P. N. Best, M. J. Hardcastle, M. Haverkorn, R. D. Kavanagh, L. Lamy, B. J. S. Pope, H. J. A. Röttgering, D. J. Schwarz, C. Tasse, R. J. van Weeren, G. J. White, P. Zarka, D. J. Bomans, A. Bonafede, M. Bonato, A. Botteon, M. Bruggen, K. T. Chyży , et al. (22 additional authors not shown)

Abstract: We present the detection of 68 sources from the most sensitive radio survey in circular polarisation conducted to date. We use the second data release of the 144 MHz LOFAR Two-metre Sky Survey to produce circularly-polarised maps with median 140 $μ$Jy beam$^{-1}$ noise and resolution of 20$''$ for $\approx$27% of the northern sky (5634 deg$^{2}$). The leakage of total intensity into circular polar… ▽ More We present the detection of 68 sources from the most sensitive radio survey in circular polarisation conducted to date. We use the second data release of the 144 MHz LOFAR Two-metre Sky Survey to produce circularly-polarised maps with median 140 $μ$Jy beam$^{-1}$ noise and resolution of 20$''$ for $\approx$27% of the northern sky (5634 deg$^{2}$). The leakage of total intensity into circular polarisation is measured to be $\approx$0.06%, and our survey is complete at flux densities $\geq1$ mJy. A detection is considered reliable when the circularly-polarised fraction exceeds 1%. We find the population of circularly-polarised sources is composed of four distinct classes: stellar systems, pulsars, active galactic nuclei, and sources unidentified in the literature. The stellar systems can be further separated into chromospherically-active stars, M dwarfs, and brown dwarfs. Based on the circularly-polarised fraction and lack of an optical counterpart, we show it is possible to infer whether the unidentified sources are likely unknown pulsars or brown dwarfs. By the completion of this survey of the northern sky, we expect to detect 300$\pm$100 circularly-polarised sources. △ Less

Submitted 19 December, 2022; originally announced December 2022.

Comments: Accepted for publication in A&A, 15 pages, 8 figures, 1 table. The catalogue will be publicly available at http://lofar-surveys.org/ and via Vizier shortly

Journal ref: A&A 670, A124 (2023)

The Host Galaxies of Hybrid Morphology Radio Sources

Authors: Andra Stroe, Victoria Catlett, Jeremy J. Harwood, Tessa Vernstrom, Beatriz Mingo

Abstract: Based on their differing radio morphologies, powerful radio galaxies can be separated into the Fanaroff-Riley I (FR-I) and II (FR-II) classes. Hybrid morphology radio sources (HyMoRS) contain morphologies consistent with each type of jet on either side: a powerful, highly relativistic FR-II-like jet terminating in a hotspot on one side and an FRI-like plume on the other. HyMoRS present a unique op… ▽ More Based on their differing radio morphologies, powerful radio galaxies can be separated into the Fanaroff-Riley I (FR-I) and II (FR-II) classes. Hybrid morphology radio sources (HyMoRS) contain morphologies consistent with each type of jet on either side: a powerful, highly relativistic FR-II-like jet terminating in a hotspot on one side and an FRI-like plume on the other. HyMoRS present a unique opportunity to study the conditions which give rise to the dichotomy. Using host galaxy properties, we conduct the first multiwavelength investigation into whether orientation can explain HyMoRS morphology. Through optical spectroscopy and mid-infrared photometry, we analyze the emission characteristics, and evaluate the broad characteristics of five HyMoRS host galaxies at intermediate redshifts (0.4 < z < 1.5). The HyMoRS host galaxies in our sample have properties consistent with typical host galaxies of FR-II sources, suggesting that the observed hybrid morphologies may be caused by a dense, cluster-like environment bending FR-II jets combined with a favorable orientation which can make one side appear similar to an FR-I jet. Our results thus support the hypothesis that HyMoRS are mainly caused by environment and orientation. △ Less

Submitted 17 October, 2022; originally announced October 2022.

Comments: Accepted for publication in the Astrophysical Journal; 12 pages, 4 figures; Comments welcome!

Cosmic evolution of low-excitation radio galaxies in the LOFAR Two-meter Sky Survey Deep Fields

Authors: R. Kondapally, P. N. Best, R. K. Cochrane, J. Sabater, K. J. Duncan, M. J. Hardcastle, P. Haskell, B. Mingo, H. J. A. Röttgering, D. J. B. Smith, W. L. Williams, M. Bonato, G. Calistro Rivera, F. Gao, C. L. Hale, K. Małek, G. K. Miley, I. Prandoni, L. Wang

Abstract: Feedback from low-excitation radio galaxies (LERGs) plays a key role in the lifecycle of massive galaxies in the local Universe; their evolution, and the impact of these active galactic nuclei on early galaxy evolution, however, remain poorly understood. We use a sample of 10481 LERGs from the first data release of the LOFAR Two-meter Sky Survey Deep Fields, covering $\sim$ 25 deg$^2$, to present… ▽ More Feedback from low-excitation radio galaxies (LERGs) plays a key role in the lifecycle of massive galaxies in the local Universe; their evolution, and the impact of these active galactic nuclei on early galaxy evolution, however, remain poorly understood. We use a sample of 10481 LERGs from the first data release of the LOFAR Two-meter Sky Survey Deep Fields, covering $\sim$ 25 deg$^2$, to present the first measurement of the evolution of the radio luminosity function (LF) of LERGs out to $z\sim2.5$; this shows relatively mild evolution. We split the LERGs into those hosted by quiescent and star-forming galaxies, finding a new dominant population of LERGs hosted by star-forming galaxies at high redshifts. The incidence of LERGs in quiescent galaxies shows a steep dependence on stellar-mass out to $z \sim1.5$, consistent with local Universe measurements of accretion occurring from cooling of hot gas haloes. The quiescent-LERGs dominate the LFs at $z<1$, showing a strong decline in space density with redshift, tracing that of the available host galaxies, while there is an increase in the characteristic luminosity. The star-forming LERG LF increases with redshift, such that this population dominates the space densities at most radio-luminosities by $z \sim 1$. The incidence of LERGs in star-forming galaxies shows a much weaker stellar-mass dependence, and increases with redshift, suggesting a different fuelling mechanism compared to their quiescent counterparts, potentially associated with the cold gas supply present in the star-forming galaxies. △ Less

Submitted 22 April, 2022; v1 submitted 15 April, 2022; originally announced April 2022.

Comments: 26 pages, 16 figures, accepted for publication in MNRAS. LF data available at: https://github.com/rohitk-10/AGN_LF_Kondapally22 . Author list error corrected in updated version

The LOFAR Two-metre Sky Survey -- V. Second data release

Authors: T. W. Shimwell, M. J. Hardcastle, C. Tasse, P. N. Best, H. J. A. Röttgering, W. L. Williams, A. Botteon, A. Drabent, A. Mechev, A. Shulevski, R. J. van Weeren, L. Bester, M. Brüggen, G. Brunetti, J. R. Callingham, K. T. Chyży, J. E. Conway, T. J. Dijkema, K. Duncan, F. de Gasperin, C. L. Hale, M. Haverkorn, B. Hugo, N. Jackson, M. Mevius , et al. (81 additional authors not shown)

Abstract: In this data release from the LOFAR Two-metre Sky Survey (LoTSS) we present 120-168MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44$^\circ$30' and 1h00m +28$^\circ$00' and spanning 4178 and 1457 square degrees respectively. The images were derived from 3,451hrs (7.6PB) of LOFAR High Band Antenna data which were corrected for th… ▽ More In this data release from the LOFAR Two-metre Sky Survey (LoTSS) we present 120-168MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44$^\circ$30' and 1h00m +28$^\circ$00' and spanning 4178 and 1457 square degrees respectively. The images were derived from 3,451hrs (7.6PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4,396,228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 6" resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144MHz have: a median rms sensitivity of 83$μ$Jy/beam; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.2"; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8mJy/beam. By creating three 16MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of +/-0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 20" resolution 120-168MHz continuum images have a median rms sensitivity of 95$μ$Jy/beam, and we estimate a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation (Stokes Q and Stokes U) image cubes consist of 480 x 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8mJy/beam at 4' and 2.2mJy/beam at 20"; we estimate the Stokes I to Stokes Q/U leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes I, Q, U and V images in addition to the calibrated uv-data. △ Less

Submitted 23 February, 2022; originally announced February 2022.

Comments: 23 figures, 1 table and 29 pages. The catalogues, images and uv-data associated with this data release are publicly available via https://lofar-surveys.org/

Do Radio Active Galactic Nuclei Reflect X-ray Binary Spectral States?

Authors: Emily Moravec, Jiri Svoboda, Abhijeet Borkar, Peter Boorman, Daniel Kynoch, Francesca Panessa, Beatriz Mingo, Matteo Guainazzi

Abstract: Over recent years there has been mounting evidence that accreting supermassive black holes in active galactic nuclei (AGN) and stellar mass black holes have similar observational signatures: thermal emission from the accretion disk, X-ray corona, and relativisitic jets. Further, there have been investigations into whether or not AGN have spectral states similar to that of X-ray binaries (XRBs) and… ▽ More Over recent years there has been mounting evidence that accreting supermassive black holes in active galactic nuclei (AGN) and stellar mass black holes have similar observational signatures: thermal emission from the accretion disk, X-ray corona, and relativisitic jets. Further, there have been investigations into whether or not AGN have spectral states similar to that of X-ray binaries (XRBs) and what parallels can be drawn between the two using a hardness-intensity diagram (HID). To address whether AGN jets might be related to accretion states as in XRBs, we explore whether populations of radio-AGN classified according to their radio jet morphology (Fanaroff-Riley classes I and II; FR I and II), excitation class (HERG and LERG), and radio jet linear extent (compact to giant) occupy different and distinct regions of the AGN hardness-intensity diagram (total luminosity vs. hardness). We do this by cross correlating 15 catalogs of radio galaxies with the desired characteristics from the literature with XMM Newton and Swift X-ray and ultraviolet (UV) source catalogs. We calculate the luminosity and hardness from the X-ray and UV photometry, place the sources on the AGN hardness-intensity diagram, and search for separation of populations and analogies with the XRB spectral state HID. We find that (a) FR Is and IIs, (b) HERGs and LERGs, (c) FR I-LERGs and FR II-HERGs occupy distinct areas of the HID at a statistically significant level (p-value < 0.05) and no clear evidence for population distinction between the different radio jet linear extents. The separation between FR I-LERG and FR II-HERG populations is the strongest in this work. Our results indicate that radio-loud AGN occupy distinct areas of the HID depending on the morphology and excitation class, showing strong similarities to XRBs. △ Less

Submitted 31 May, 2022; v1 submitted 22 February, 2022; originally announced February 2022.

Comments: 24 pages with 10 figures. Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 662, A28 (2022)

Accretion mode versus radio morphology in the LOFAR Deep Fields

Authors: B. Mingo, J. H. Croston, P. N. Best, K. J. Duncan, M. J. Hardcastle, R. Kondapally, I. Prandoni, J. Sabater, T. W. Shimwell, W. L. Williams, R. D. Baldi, M. Bonato, M. Bondi, P. Dabhade, G. Gürkan, J. Ineson, M. Magliocchetti, G. Miley, J. C. S. Pierce, H. J. A. Röttgering

Abstract: Radio-loud active galaxies have two accretion modes [radiatively inefficient (RI) and radiatively efficient (RE)], with distinct optical and infrared signatures, and two jet dynamical behaviours, which in arcsec- to arcmin-resolution radio surveys manifest primarily as centre- or edge-brightened structures [Fanaroff-Riley (FR) class I and II]. The nature of the relationship between accretion mode… ▽ More Radio-loud active galaxies have two accretion modes [radiatively inefficient (RI) and radiatively efficient (RE)], with distinct optical and infrared signatures, and two jet dynamical behaviours, which in arcsec- to arcmin-resolution radio surveys manifest primarily as centre- or edge-brightened structures [Fanaroff-Riley (FR) class I and II]. The nature of the relationship between accretion mode and radio morphology (FR class) has been the subject of long debate. We present a comprehensive investigation of this relationship for a sample of 286 well-resolved radio galaxies in the LOFAR Two-metre Sky Survey Deep Fields (LoTSS-Deep) first data release, for which robust morphological and accretion mode classifications have been made. We find that two-thirds of luminous FRII radio galaxies are RI, and identify no significant differences in the visual appearance or source dynamic range (peak/mean surface brightness) of the RI and RE FRIIs, demonstrating that both RI and RE systems can produce FRII structures. We also find a significant population of low-luminosity FRIIs (predominantly RI), supporting our earlier conclusion that FRII radio structures can be produced at all radio luminosities. We demonstrate that in the luminosity range where both morphologies are present, the probability of producing FRI or FRII radio morphology is directly linked to stellar mass, while across all morphologies and luminosities, RE accretion occurs in systems with high specific star formation rate, presumably because this traces fuel availability. In summary, the relationship between accretion mode and radio morphology is very indirect, with host-galaxy environment controlling these two key parameters in different ways. △ Less

Submitted 17 February, 2022; v1 submitted 12 January, 2022; originally announced January 2022.

Comments: 22 pages, 17 figures, 7 tables. Accepted for publication in MNRAS. Update with minor changes to match published version

VLA Snapshot Continuum Survey of FRI Quasar Candidates Selected from the LOFAR Two-Metre Sky Survey (LoTSS)

Authors: Gülay Gürkan, Judith Croston, Martin Hardcastle, Vijay Mahatma, Beatriz Mingo, Wendy Williams

Abstract: The radiative and jet power in active galactic nuclei is generated by accretion of material on to supermassive galactic-centre black holes. For quasars, where the radiative power is by definition very high, objects with high radio luminosities form around 10 per cent of the population, although it is not clear whether this is a stable phase. Traditionally, quasars with high radio luminosities have… ▽ More The radiative and jet power in active galactic nuclei is generated by accretion of material on to supermassive galactic-centre black holes. For quasars, where the radiative power is by definition very high, objects with high radio luminosities form around 10 per cent of the population, although it is not clear whether this is a stable phase. Traditionally, quasars with high radio luminosities have been thought to present jets with edge-brightened morphology (Fanaroff-Riley II - FR II) due to the limitations of previous radio surveys (i.e., FRIs were not observed as part of the quasar population). The LOw Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) with its unprecedented sensitivity and resolution covering wide sky areas has enabled the first systematic selection and investigation of quasars with core-brightened morphology (Fanaroff-Riley I - FR). We carried out a Very Large Array (VLA) snapshot survey to reveal inner structures of jets in selected quasar candidates; 15 (25 per cent) out of 60 sources show clear inner jet structures that are diagnostic of FRI jets and 13 quasars (around 22 per cent) show extended structures similar to those of FRI jets. Black hole masses and Eddington ratios do not show a clear difference between FRI and FRII quasars. FRII quasars tend to have higher jet powers than FRI quasars. Our results show that the occurrence of FRI jets in powerful radiatively efficient systems is not common, probably mainly due to two factors: galaxy environment and jet power. △ Less

Submitted 24 December, 2021; originally announced December 2021.

Comments: 39 pages, 8 figures, 5 tables, Accepted the Special Issue "A New Window on the Radio Emission from Galaxies, Galaxy Clusters and Cosmic Web: Current Status and Perspectives" of MDPI Galaxies; Galaxies 2022, 10(1), 2; 10.3390/galaxies10010002

The Application of Ridgelines in Extended Radio Source Cross-Identification

Authors: B. Barkus, J. H. Croston, J. Piotrowska, B. Mingo, P. N. Best, M. J. Hardcastle, R. I. J. Mostert, H. J. A. Röttgering, J. Sabater, B. Webster, W. L. Williams

Abstract: Extended radio sources are an important minority population in modern deep radio surveys, because they enable detailed investigation of the physics governing radio-emitting regions such as active galaxies and their environments. Cross-identification of radio sources with optical host galaxies is challenging for this extended population, due to their morphological complexity and multiple potential… ▽ More Extended radio sources are an important minority population in modern deep radio surveys, because they enable detailed investigation of the physics governing radio-emitting regions such as active galaxies and their environments. Cross-identification of radio sources with optical host galaxies is challenging for this extended population, due to their morphological complexity and multiple potential counterparts. In the first data release of the Low-frequency array (LOFAR) Two-metre Sky Survey (LoTSS DR1) the automated likelihood ratio for compact sources was supplemented by a citizen science visual identification process for extended sources. In this paper we present a novel method for automating the host identification of extended sources by using ridgelines, which trace the assumed direction of fluid-flow through the points of highest flux density. Applying a new code, RL-Xid, to LoTSS DR1, we demonstrate that ridgelines are versatile; by providing information about spatial structure and brightness distributions, they can be used both for optical host identification and morphological studies in radio surveys. RL-Xid draws ridgelines for 85 per cent of sources brighter than 10 mJy and larger than 15 arcsec, with an improved performance of 96 per cent for the subset >30 mJy and >60 arcsec. Using a sample of sources with known hosts from LoTSS DR1, we demonstrate that RL-Xid successfully identifies the host for 98 per cent of the sources with successfully drawn ridgelines, and performs at a comparable level to visual identification via citizen science. We also demonstrate that ridgeline brightness profiles provide a promising automated technique for morphological classification. △ Less

Submitted 12 October, 2021; v1 submitted 11 October, 2021; originally announced October 2021.

Comments: 16 pages, 7 figures, accepted for publication in MNRAS

Investigating the spectra and physical nature of galaxy scale jets

Authors: B. Webster, J. H. Croston, J. J. Harwood, R. D. Baldi, M. J. Hardcastle, B. Mingo, H. J. A. Rottgering

Abstract: Previous studies have shown that physically small, low-luminosity radio galaxies, which we refer to as galaxy scale jets (GSJ), could potentially have a significant effect upon the host galaxy's evolution. Using 6 arcsec resolution images taken from the first release of the LOFAR Two Metre Sky Survey (LoTSS DR1), we identified a representative sample of nine potential GSJ for which we obtained hig… ▽ More Previous studies have shown that physically small, low-luminosity radio galaxies, which we refer to as galaxy scale jets (GSJ), could potentially have a significant effect upon the host galaxy's evolution. Using 6 arcsec resolution images taken from the first release of the LOFAR Two Metre Sky Survey (LoTSS DR1), we identified a representative sample of nine potential GSJ for which we obtained high-resolution, 2-4 GHz data using the Karl G. Jansky Very Large Array (VLA). Using these data we aim to verify the GSJ nature of these sources as well as investigating the potential role of feedback. Our VLA images reveal a diversity of structures, confirm the hosts for four of the sources and find that a fifth is the first known example of a galaxy-scale remnant showing that some radio galaxies never grow beyond the GSJ stage. We also derive spectral ages and the first estimates of the lobe expansion speeds of GSJ. We find our GSJ have maximum spectral ages of 60 Myr with most between about 5 and 20 Myr, consistent with being located along an evolutionary path joining compact sources and larger radio galaxies. We find lobe advance speeds a few times the local sound speed, with most GSJ predicted to be driving strong shocks into their environment and having a significant impact upon the host's evolution. Our discovery of a remnant GSJ, which will eventually transfer all of its energy directly into the local environment, represents an important and previously hidden aspect of AGN life cycles. △ Less

Submitted 8 October, 2021; originally announced October 2021.

Comments: 19 pages, 12 figures, accepted by MNRAS

Radio Morphology of Red Geysers

Authors: Namrata Roy, Emily Moravec, Kevin Bundy, Martin J. Hardcastle, Gülay Gürkan, Ranieri D. Baldi, Sarah K. Leslie, Karen Masters, Joseph Gelfand, Rogerio Riffel, Rogemar A. Riffel, Beatriz Mingo, Alexander Drabent

Abstract: We present 150 MHz, 1.4 GHz, and 3 GHz radio imaging (LoTSS, FIRST and VLASS) and spatially resolved ionized gas characteristics (SDSS IV-MaNGA) for 140 local ($z<0.1$) early-type "red geyser" galaxies. These galaxies have low star formation activity (SFR $\sim \rm 0.01\ M_{\odot} yr^{-1}$), but show unique extended patterns in spatially-resolved emission line maps that have been interpreted as la… ▽ More We present 150 MHz, 1.4 GHz, and 3 GHz radio imaging (LoTSS, FIRST and VLASS) and spatially resolved ionized gas characteristics (SDSS IV-MaNGA) for 140 local ($z<0.1$) early-type "red geyser" galaxies. These galaxies have low star formation activity (SFR $\sim \rm 0.01\ M_{\odot} yr^{-1}$), but show unique extended patterns in spatially-resolved emission line maps that have been interpreted as large-scale ionized winds driven by active galactic nuclei (AGN). In this work we confirm that red geysers host low-luminosity radio sources ($\rm L_{1.4GHz} \sim 10^{22} W Hz^{-1}$). Out of 42 radio-detected red geysers, 32 are spatially resolved in LoTSS and FIRST, with radio sizes varying between $\sim 5-25$ kpc. Three sources have radio sizes exceeding 40 kpc. A majority display a compact radio morphology and are consistent with either low-power compact radio sources ("FR0" galaxies) or "radio-quiet quasars". They may be powered by small-scale AGN-driven jets which remain unresolved at the current $5"$ resolution of radio data. The extended radio sources, not belonging to the "compact" morphological class, exhibit steeper spectra with a median spectral index of $-0.67$ indicating the dominance of lobed components. The red geysers hosting extended radio sources also have the lowest specific star formation rates, suggesting they either have a greater impact on the surrounding interstellar medium or are found in more massive halos on average. The degree of alignment of the ionized wind cone and the extended radio features are either 0$^{\circ}$ or 90$^{\circ}$, indicating possible interaction between the interstellar medium and the central radio AGN. △ Less

Submitted 6 September, 2021; originally announced September 2021.

Comments: 23 pages, 14 figures. Accepted for publication in The Astrophysical Journal

Characterising the extended morphologies of BL Lacs at 144 MHz with LOFAR

Authors: Seán Mooney, Francesco Massaro, John Quinn, Alessandro Capetti, Ranieri D. Baldi, Gülay Gürkan, Martin J. Hardcastle, Cathy Horellou, Beatriz Mingo, Raffaella Morganti, Shane O'Sullivan, Urszula Pajdosz-Śmierciak, Mamta Pandey-Pommier, Huub Röttgering

Abstract: We present a morphological and spectral study of a sample of 99 BL Lacs using the LOFAR Two-Metre Sky Survey Second Data Release (LDR2). Extended emission has been identified at gigahertz frequencies around BL Lacs, but with LDR2 it is now possible to systematically study their morphologies at 144 MHz, where more diffuse emission is expected. LDR2 reveals the presence of extended radio structures… ▽ More We present a morphological and spectral study of a sample of 99 BL Lacs using the LOFAR Two-Metre Sky Survey Second Data Release (LDR2). Extended emission has been identified at gigahertz frequencies around BL Lacs, but with LDR2 it is now possible to systematically study their morphologies at 144 MHz, where more diffuse emission is expected. LDR2 reveals the presence of extended radio structures around 66/99 of the BL Lac nuclei, with angular extents ranging up to 115 arcseconds, corresponding to spatial extents of 410 kpc. The extended emission is likely to be both unbeamed diffuse emission and beamed emission associated with relativistic bulk motion in jets. The spatial extents and luminosities of the extended emission are consistent with the AGN unification scheme where BL Lacs correspond to low-excitation radio galaxies with the jet axis aligned along the line-of-sight. While extended emission is detected around the majority of BL Lacs, the median 144-1400 MHz spectral index and core dominance at 144 MHz indicate that the core component contributes ~42% on average to the total low-frequency flux density. A stronger correlation was found between the 144 MHz core flux density and the gamma-ray photon flux (r = 0.69) compared to the 144 MHz extended flux density and the gamma-ray photon flux (r = 0.42). This suggests that the radio-to-gamma-ray connection weakens at low radio frequencies because the population of particles that give rise to the gamma-ray flux are distinct from the electrons producing the diffuse synchrotron emission associated with spatially-extended features. △ Less

Submitted 5 September, 2021; originally announced September 2021.

Comments: 15 pages, 9 figures, accepted for publication in the Astrophysical Journal Supplement Series

Clusters' far-reaching influence on narrow-angle tail radio galaxies

Authors: K de Vos, N. A. Hatch, M. R. Merrifield, B. Mingo

Abstract: In order to study the ram-pressure interaction between radio galaxies and the intracluster medium, we analyse a sample of 208 highly-bent narrow-angle tail radio sources (NATs) in clusters, detected by the LOFAR Two-metre Sky Survey. For NATs within $7\,R_{500}$ of the cluster centre, we find that their tails are distributed anisotropically with a strong tendency to be bent radially away from the… ▽ More In order to study the ram-pressure interaction between radio galaxies and the intracluster medium, we analyse a sample of 208 highly-bent narrow-angle tail radio sources (NATs) in clusters, detected by the LOFAR Two-metre Sky Survey. For NATs within $7\,R_{500}$ of the cluster centre, we find that their tails are distributed anisotropically with a strong tendency to be bent radially away from the cluster, which suggests that they are predominantly on radially inbound orbits. Within $0.5\,R_{500}$, we also observe an excess of NATs with their jets bent towards the cluster core, indicating that these outbound sources fade away soon after passing pericentre. For the subset of NATs with spectroscopic redshifts, we find the radial bias in the jet angles exists even out to $10\,R_{500}$, far beyond the virial radius. The presence of NATs at such large radii implies that significant deceleration of the accompanying inflowing intergalactic medium must be occurring there to create the ram pressure that bends the jets, and potentially even triggers the radio source. △ Less

Submitted 1 July, 2021; originally announced July 2021.

Comments: 5 pages, 4 figures, paper accepted for publication by MNRAS

The LOFAR LBA Sky Survey I. survey description and preliminary data release

Authors: F. de Gasperin, W. L. Williams, P. Best, M. Bruggen, G. Brunetti, V. Cuciti, T. J. Dijkema, M. J. Hardcastle, M. J. Norden, A. Offringa, T. Shimwell, R. van Weeren, D. Bomans, A. Bonafede, A. Botteon, J. R. Callingham, R. Cassano, K. T. Chyzy, K. L. Emig, H. Edler, M. Haverkorn, G. Heald, V. Heesen, M. Iacobelli, H. T. Intema , et al. (16 additional authors not shown)

Abstract: LOFAR is the only radio telescope that is presently capable of high-sensitivity, high-resolution (<1 mJy/b and <15") observations at ultra-low frequencies (<100 MHz). To utilise these capabilities, the LOFAR Surveys Key Science Project is undertaking a large survey to cover the entire northern sky with Low Band Antenna (LBA) observations. The LOFAR LBA Sky Survey (LoLSS) aims to cover the entire n… ▽ More LOFAR is the only radio telescope that is presently capable of high-sensitivity, high-resolution (<1 mJy/b and <15") observations at ultra-low frequencies (<100 MHz). To utilise these capabilities, the LOFAR Surveys Key Science Project is undertaking a large survey to cover the entire northern sky with Low Band Antenna (LBA) observations. The LOFAR LBA Sky Survey (LoLSS) aims to cover the entire northern sky with 3170 pointings in the frequency range 42-66 MHz, at a resolution of 15 arcsec and at a sensitivity of 1 mJy/b. Here we outline the survey strategy, the observational status, the current calibration techniques, and briefly describe several scientific motivations. We also describe the preliminary public data release. The preliminary images were produced using a fully automated pipeline that aims to correct all direction-independent effects in the data. Whilst the direction-dependent effects, such as those from the ionosphere, are not yet corrected, the images presented in this work are still 10 times more sensitive than previous surveys available at these low frequencies. The preliminary data release covers 740 sqdeg around the HETDEX spring field region at a resolution of 47" with a median noise level of 5 mJy/b. The images and the catalogue with 25,247 sources are publicly released. We demonstrate that the system is capable of reaching an rms noise of 1 mJy/b and the resolution of 15" once direction-dependent effects are corrected for. LoLSS will provide the ultra-low-frequency information for hundreds of thousands of radio sources, providing critical spectral information and producing a unique dataset that can be used for a wide range of science topics such as: the search for high redshift galaxies and quasars, the study of the magnetosphere of exoplanets, and the detection of the oldest populations of cosmic-rays in galaxies, clusters of galaxies, and from AGN activity. △ Less

Submitted 18 February, 2021; originally announced February 2021.

Comments: 19 pages, 14 figures, Accepted A&A, catalogue and images on www.lofar-surveys.org

The best of both worlds: Combining LOFAR and Apertif to derive resolved radio spectral index images

Authors: R. Morganti, T. A. Oosterloo, M. Brienza, N. Jurlin, I. Prandoni, E. Orru', S. S. Shabala, E. A. K. Adams, B. Adebahr, P. N. Best, A. H. W. M. Coolen, S. Damstra, W. J. G. de Blok, F. de Gasperin, H. Denes, M. Hardcastle, K. M. Hess, B. Hut, R. Kondapally, A. M. Kutkin, G. M. Loose, D. M. Lucero, Y. Maan, F. M. Maccagni, B. Mingo , et al. (14 additional authors not shown)

Abstract: Supermassive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei is crucial for understanding the impact of the energy they release on the host galaxy. For radio AGN, this can be done by identifying dying (remnant) and restarted radio galaxies from their radio spectral properties. Using the combination… ▽ More Supermassive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei is crucial for understanding the impact of the energy they release on the host galaxy. For radio AGN, this can be done by identifying dying (remnant) and restarted radio galaxies from their radio spectral properties. Using the combination of images at 1400 MHz produced by Apertif, the new phased-array feed receiver installed on the Westerbork Synthesis Radio Telescope, and images at 150 MHz provided by LOFAR, we have derived resolved spectral index images (at a resolution of ~15 arcsec) for all the sources within ~6 deg^2 area of the Lockman Hole region. We were able to select 15 extended radio sources with emission (partly or entirely) characterised by extremely steep spectral indices (steeper than 1.2). These objects represent radio sources in the remnant or the restarted phases of their life cycle. Our findings suggest this cycle to be relatively fast. They also show a variety of properties relevant for modelling the evolution of radio galaxies. For example, the restarted activity can occur while the remnant structure from a previous phase of activity is still visible. This provides constraints on the duration of the 'off' (dying) phase. In extended remnants with ultra-steep spectra at low frequencies, the activity likely stopped a few hundred megayears ago, and they correspond to the older tail of the age distribution of radio galaxies, in agreement with simulations of radio source evolution. We find remnant radio sources with a variety of structures (from double-lobed to amorphous), suggesting different types of progenitors. The present work sets the stage for exploiting low-frequency spectral index studies of extended sources by taking advantage of the large areas common to the LOFAR and the Apertif surveys. △ Less

Submitted 16 November, 2020; originally announced November 2020.

Comments: Accepted for publication in A&A. This paper is part of the 1st data release of the LoTSS Deep Fields. 17 pages, 10 figures

The LOFAR Two Metre Sky Survey: Deep Fields Data Release 1 -- III. Host-galaxy identifications and value added catalogues

Authors: R. Kondapally, P. N. Best, M. J. Hardcastle, D. Nisbet, M. Bonato, J. Sabater, K. J. Duncan, I. McCheyne, R. K. Cochrane, R. A. A. Bowler, W. L. Williams, T. W. Shimwell, C. Tasse, J. H. Croston, A. Goyal, M. Jamrozy, M. J. Jarvis, V. H. Mahatma, H. J. A. R\öttgering, D. J. B. Smith, A. Wo\łowska, M. Bondi, M. Brienza, M. J. I. Brown, M. Br\üggen , et al. (18 additional authors not shown)

Abstract: We present the source associations, cross-identifications, and multi-wavelength properties of the faint radio source population detected in the deep tier of the LOFAR Two Metre Sky Survey (LoTSS): the LoTSS Deep Fields. The first LoTSS Deep Fields data release consists of deep radio imaging at 150~MHz of the ELAIS-N1, Lockman Hole, and Boötes fields, down to RMS sensitives of around 20, 22, and 32… ▽ More We present the source associations, cross-identifications, and multi-wavelength properties of the faint radio source population detected in the deep tier of the LOFAR Two Metre Sky Survey (LoTSS): the LoTSS Deep Fields. The first LoTSS Deep Fields data release consists of deep radio imaging at 150~MHz of the ELAIS-N1, Lockman Hole, and Boötes fields, down to RMS sensitives of around 20, 22, and 32$~μ$Jy\,beam$^{-1}$, respectively. These fields are some of the best studied extra-galactic fields in the northern sky, with existing deep, wide-area panchromatic photometry from X-ray to infrared wavelengths, covering a total of $\approx$~26~\mbox{deg$^{2}$}. We first generated improved multi-wavelength catalogues in ELAIS-N1 and Lockman Hole; combined with the existing catalogue for Boötes, we present forced, matched aperture photometry for over 7.2 million sources across the three fields. We identified multi-wavelength counterparts to the radio detected sources, using a combination of the Likelihood Ratio method and visual classification, which greatly enhances the scientific potential of radio surveys and allows for the characterisation of the photometric redshifts and the physical properties of the host galaxies. The final radio-optical cross-matched catalogue consists of 81\,951 radio-detected sources, with counterparts identified and multi-wavelength properties presented for 79\,820 ($>$97\%) sources. We also examine the properties of the host galaxies, and through stacking analysis find that the radio population with no identified counterpart is likely dominated by AGN at $z\sim3-4$. This dataset contains one of the largest samples of radio-selected star-forming galaxies and active galactic nuclei (AGN) at these depths, making it ideal for studying the history of star-formation, and the evolution of galaxies and AGN across cosmic time. △ Less

Submitted 16 November, 2020; originally announced November 2020.

Comments: 34 pages, 14 figures and 14 tables. Accepted for publication in A&A special issue. This paper is part of the 1st data release of the LoTSS Deep Fields. Electronic data catalogues will be made available on journal publication

Journal ref: A&A 648, A3 (2021)

Unveiling the rarest morphologies of the LOFAR Two-metre Sky Survey radio source population with self-organised maps

Authors: Rafaël I. J. Mostert, Kenneth J. Duncan, Huub J. A. Röttgering, Kai L. Polsterer, Philip N. Best, Marisa Brienza, Marcus Brüggen, Martin J. Hardcastle, Nika Jurlin, Beatriz Mingo, Raffaella Morganti, Tim Shimwell, Dan Smith, Wendy L. Williams

Abstract: The Low Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) is a low-frequency radio continuum survey of the Northern sky at an unparalleled resolution and sensitivity. In order to fully exploit this huge dataset and those produced by the Square Kilometre Array in the next decade, automated methods in machine learning and data-mining will be increasingly essential both for morphological classific… ▽ More The Low Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) is a low-frequency radio continuum survey of the Northern sky at an unparalleled resolution and sensitivity. In order to fully exploit this huge dataset and those produced by the Square Kilometre Array in the next decade, automated methods in machine learning and data-mining will be increasingly essential both for morphological classifications and for identifying optical counterparts to the radio sources. Using self-organising maps (SOMs), a form of unsupervised machine learning, we created a dimensionality reduction of the radio morphologies for the $\sim$25k extended radio continuum sources in the LoTSS first data release, which is only $\sim$2 percent of the final LoTSS survey. We made use of \textsc{PINK}, a code which extends the SOM algorithm with rotation and flipping invariance, increasing its suitability and effectiveness for training on astronomical sources. After training, the SOMs can be used for a wide range of science exploitation and we present an illustration of their potential by finding an arbitrary number of morphologically rare sources in our training data (424 square degrees) and subsequently in an area of the sky ($\sim$5300 square degrees) outside the training data. Objects found in this way span a wide range of morphological and physical categories: extended jets of radio active galactic nuclei, diffuse cluster haloes and relics, and nearby spiral galaxies. Finally, to enable accessible, interactive, and intuitive data exploration, we showcase the LOFAR-PyBDSF Visualisation Tool, which allows users to explore the LoTSS dataset through the trained SOMs. △ Less

Submitted 11 November, 2020; originally announced November 2020.

Comments: 26 pages; accepted for publication in A&A

Journal ref: A&A 645, A89 (2021)

Extended X-ray emission around FR II radio galaxies: hotspots, lobes and galaxy clusters

Authors: Ana Jimenez-Gallardo, Francesco Massaro, Alessandro Paggi, Raffaele D'Abrusco, M. Almudena Prieto, Harold A. Peña-Herazo, Vittoria Berta, Federica Ricci, Chiara Stuardi, Belinda J. Wilkes, Christopher P. O'Dea, Stefi A. Baum, Ralph P. Kraft, William R. Froman, Christine Jones, Beatriz Mingo, Elisabetta Liuzzo, Barbara Balmaverde, Alessandro Capetti, Valentina Missaglia, Martin J. Hardcastle, Ranieri D. Baldi, Leah K. Morabito

Abstract: We present a systematic analysis of the extended X-ray emission discovered around 35 FR II radio galaxies from the revised Third Cambridge catalog (3CR) Chandra Snapshot Survey with redshifts between 0.05 to 0.9. We aimed to (i) test for the presence of extended X-ray emission around FR II radio galaxies, (ii) investigate if the extended emission origin is due to Inverse Compton scattering of se… ▽ More We present a systematic analysis of the extended X-ray emission discovered around 35 FR II radio galaxies from the revised Third Cambridge catalog (3CR) Chandra Snapshot Survey with redshifts between 0.05 to 0.9. We aimed to (i) test for the presence of extended X-ray emission around FR II radio galaxies, (ii) investigate if the extended emission origin is due to Inverse Compton scattering of seed photons arising from the Cosmic Microwave Background (IC/CMB) or to thermal emission from an intracluster medium (ICM) and (iii) test the impact of this extended emission on hotspot detection. We investigated the nature of the extended X-ray emission by studying its morphology and compared our results with low-frequency radio observations (i.e., $\sim$150 MHz), in the TGSS and LOFAR archives, as well as with optical images from Pan-STARRS. In addition, we optimized a search for X-ray counterparts of hotspots in 3CR FR II radio galaxies. We found statistically significant extended emission ($>$3$σ$ confidence level) along the radio axis for $\sim$90%, and in the perpendicular direction for $\sim$60% of our sample. We confirmed the detection of 7 hotspots in the 0.5 - 3 keV. In the cases where the emission in the direction perpendicular to the radio axis is comparable to that along the radio axis, we suggest that the underlying radiative process is thermal emission from ICM. Otherwise, the dominant radiative process is likely non-thermal IC/CMB emission from lobes. We found that non-thermal IC/CMB is the dominant process in $\sim$70% of the sources in our sample, while thermal emission from the ICM dominates in $\sim$15% of them. △ Less

Submitted 9 November, 2020; originally announced November 2020.

Comments: 29 pages, 11 figures, ApJS accepted, pre-proof version

A population of galaxy-scale jets discovered using LOFAR

Authors: B. Webster, J. H. Croston, B. Mingo, R. D. Baldi, B. Barkus, G. Gurkan, M. J. Hardcastle, R. Morganti, H. J. A. Rottgering, J. Sabater, T. W. Shimwell, C. Tasse, G. J. White

Abstract: The effects of feedback from high luminosity radio-loud AGN have been extensively discussed in the literature, but feedback from low-luminosity radio-loud AGN is less well understood. The advent of high sensitivity, high angular resolution, large field of view telescopes such as LOFAR is now allowing wide-area studies of such faint sources for the first time. Using the first data release of the LO… ▽ More The effects of feedback from high luminosity radio-loud AGN have been extensively discussed in the literature, but feedback from low-luminosity radio-loud AGN is less well understood. The advent of high sensitivity, high angular resolution, large field of view telescopes such as LOFAR is now allowing wide-area studies of such faint sources for the first time. Using the first data release of the LOFAR Two Metre Sky Survey (LoTSS) we report on our discovery of a population of 195 radio galaxies with 150 MHz luminosities between $3\times10^{22}$ and $1.5\times10^{25}\text{ W Hz}^{-1}$ and total radio emission no larger than 80 kpc. These objects, which we term galaxy-scale jets (GSJ), are small enough to be directly influencing the evolution of the host on galaxy scales. We report upon the typical host properties of our sample, finding that 9 per cent are hosted by spirals with the remainder being hosted by elliptical galaxies. Two of the spiral-hosted GSJ are highly unusual with low radio luminosities and FRII-like morphology. The host properties of our GSJ show that they are ordinary AGN observed at a stage in their life shortly after the radio emission has expanded beyond the central regions of the host. Based on our estimates, we find that about half of our GSJ have internal radio lobe energy within an order of magnitude of the ISM energy so that, even ignoring any possible shocks, GSJ are energetically capable of affecting the evolution of the host. The current sample of GSJ will grow in size with future releases of LoTSS and can also form the basis for further studies of feedback from low-luminosity radio sources. △ Less

Submitted 2 November, 2020; originally announced November 2020.

Comments: 23 pages, accepted by MNRAS

The life cycle of radio galaxies in the LOFAR Lockman Hole field

Authors: N. Jurlin, R. Morganti, M. Brienza, S. Mandal, N. Maddox, K. J. Duncan, S. S. Shabala, M. J. Hardcastle, I. Prandoni, H. J. A. Röttgering, V. Mahatma, P. N. Best, B. Mingo, J. Sabater, T. W. Shimwell, C. Tasse

Abstract: Radio galaxies are known to go through cycles of activity, where phases of apparent quiescence can be followed by repeated activity of the central supermassive black hole. A better understanding of this cycle is crucial for ascertaining the energetic impact that the jets have on the host galaxy, but little is known about it. We used deep LOFAR images at 150 MHz of the Lockman Hole extragalactic fi… ▽ More Radio galaxies are known to go through cycles of activity, where phases of apparent quiescence can be followed by repeated activity of the central supermassive black hole. A better understanding of this cycle is crucial for ascertaining the energetic impact that the jets have on the host galaxy, but little is known about it. We used deep LOFAR images at 150 MHz of the Lockman Hole extragalactic field to select a sample of 158 radio sources with sizes $> 60^{\prime\prime}$ in different phases of their jet life cycle. Using a variety of criteria (e.g. core prominence combined with low-surface brightness of the extended emission and steep spectrum of the central region) we selected a subsample of candidate restarted radio galaxies representing between 13% and 15% of the 158 sources of the main sample. We compare their properties to the rest of the sample, which consists of remnant candidates and active radio galaxies. Optical identifications and characterisations of the host galaxies indicate similar properties for candidate restarted, remnant, and active radio galaxies, suggesting that they all come from the same parent population. The fraction of restarted radio galaxies is slightly higher with respect to remnants, suggesting that the restarted phase can often follow after a relatively short remnant phase (the duration of the remnant phase being a few times 10$^{7}$ years). This confirms that the remnant and restarted phases are integral parts of the life cycle of massive elliptical galaxies. A preliminary investigation does not suggest a strong dependence of this cycle on the environment surrounding any given galaxy. △ Less

Submitted 20 April, 2020; originally announced April 2020.

Comments: 16 pages, 9 figures, 4 tables, A&A accepted, companion paper to Shabala et al., also in today arXiv posting

Journal ref: A&A 638, A34 (2020)

The high energy universe at ultra-high resolution: the power and promise of X-ray interferometry

Authors: Phil Uttley, Roland den Hartog, Cosimo Bambi, Didier Barret, Stefano Bianchi, Michal Bursa, Massimo Cappi, Piergiorgio Casella, Webster Cash, Elisa Costantini, Thomas Dauser, Maria Diaz Trigo, Keith Gendreau, Victoria Grinberg, Jan-Willem den Herder, Adam Ingram, Erin Kara, Sera Markoff, Beatriz Mingo, Francesca Panessa, Katja Poppenhäger, Agata Różańska, Jiri Svoboda, Ralph Wijers, Richard Willingale , et al. (2 additional authors not shown)

Abstract: We propose the development of X-ray interferometry (XRI), to reveal the universe at high energies with ultra-high spatial resolution. With baselines which can be accommodated on a single spacecraft, XRI can reach 100 $μ$as resolution at 10 Å(1.2 keV) and 20 $μ$as at 2 Å(6 keV), enabling imaging and imaging-spectroscopy of (for example) X-ray coronae of nearby accreting supermassive black holes (SM… ▽ More We propose the development of X-ray interferometry (XRI), to reveal the universe at high energies with ultra-high spatial resolution. With baselines which can be accommodated on a single spacecraft, XRI can reach 100 $μ$as resolution at 10 Å(1.2 keV) and 20 $μ$as at 2 Å(6 keV), enabling imaging and imaging-spectroscopy of (for example) X-ray coronae of nearby accreting supermassive black holes (SMBH) and the SMBH `shadow'; SMBH accretion flows and outflows; X-ray binary winds and orbits; stellar coronae within ~100 pc and many exoplanets which transit across them. For sufficiently luminous sources XRI will resolve sub-pc scales across the entire observable universe, revealing accreting binary SMBHs and enabling trigonometric measurements of the Hubble constant with X-ray light echoes from quasars or explosive transients. A multi-spacecraft `constellation' interferometer would resolve well below 1 $μ$as, enabling SMBH event horizons to be resolved in many active galaxies and the detailed study of the effects of strong field gravity on the dynamics and emission from accreting gas close to the black hole. △ Less

Submitted 8 August, 2019; originally announced August 2019.

Comments: White Paper submitted in response to ESA's Voyage 2050 call

Voyage through the Hidden Physics of the Cosmic Web

Authors: A. Simionescu, S. Ettori, N. Werner, D. Nagai, F. Vazza, H. Akamatsu, C. Pinto, J. de Plaa, N. Wijers, D. Nelson, E. Pointecouteau, G. W. Pratt, D. Spiga, G. Vacanti, E. Lau, M. Rossetti, F. Gastaldello, V. Biffi, E. Bulbul, M. J. Collon, J. W. den Herder, D. Eckert, F. Fraternali, B. Mingo, G. Pareschi , et al. (5 additional authors not shown)

Abstract: The majority of the ordinary matter in the local Universe has been heated by strong structure formation shocks and resides in a largely unexplored hot, diffuse, X-ray emitting plasma that permeates the halos of galaxies, galaxy groups and clusters, and the cosmic web. We propose a next-generation "Cosmic Web Explorer" that will permit a complete and exhaustive understanding of these unseen baryons… ▽ More The majority of the ordinary matter in the local Universe has been heated by strong structure formation shocks and resides in a largely unexplored hot, diffuse, X-ray emitting plasma that permeates the halos of galaxies, galaxy groups and clusters, and the cosmic web. We propose a next-generation "Cosmic Web Explorer" that will permit a complete and exhaustive understanding of these unseen baryons. This will be the first mission capable to reach the accretion shocks located several times farther than the virial radii of galaxy clusters, and reveal the out-of-equilibrium parts of the intra-cluster medium which are live witnesses to the physics of cosmic accretion. It will also enable a view of the thermodynamics, kinematics, and chemical composition of the circumgalactic medium in galaxies with masses similar to the Milky Way, at the same level of detail that $Athena$ will unravel for the virialized regions of massive galaxy clusters, delivering a transformative understanding of the evolution of those galaxies in which most of the stars and metals in the Universe were formed. Finally, the proposed X-ray satellite will connect the dots of the large-scale structure by mapping, at high spectral resolution, as much as 100% of the diffuse gas hotter than $10^6$ K that fills the filaments of the cosmic web at low redshifts, down to an over-density of 1, both in emission and in absorption against the ubiquitous cosmic X-ray background, surveying at least 1600 square degrees over 5 years in orbit. This requires a large effective area (~10 m$^2$ at 1 keV) over a large field of view ($\sim1$ deg$^2$), a megapixel cryogenic microcalorimeter array providing integral field spectroscopy with a resolving power $E/ΔE$ = 2000 at 0.6 keV and a spatial resolution of 5 arcsec in the soft X-ray band, and a low and stable instrumental background ensuring high sensitivity to faint, extended emission. △ Less

Submitted 26 April, 2021; v1 submitted 5 August, 2019; originally announced August 2019.

Comments: White paper submitted in response to ESA's Voyage 2050 Call. Accepted for publication in Experimental Astronomy

Revisiting the Fanaroff-Riley dichotomy and radio-galaxy morphology with the LOFAR Two-Metre Sky Survey (LoTSS)

Authors: B. Mingo, J. H. Croston, M. J. Hardcastle, P. N. Best, K. J. Duncan, R. Morganti, H. J. A. Rottgering, J. Sabater, T. W. Shimwell, W. L. Williams, M. Brienza, G. Gurkan, V. H. Mahatma, L. K. Morabito, I. Prandoni, M. Bondi, J. Ineson, S. Mooney

Abstract: The relative positions of the high and low surface brightness regions of radio-loud active galaxies in the 3CR sample were found by Fanaroff and Riley to be correlated with their luminosity. We revisit this canonical relationship with a sample of 5805 extended radio-loud AGN from the LOFAR Two-Metre Sky Survey (LoTSS), compiling the most complete dataset of radio-galaxy morphological information o… ▽ More The relative positions of the high and low surface brightness regions of radio-loud active galaxies in the 3CR sample were found by Fanaroff and Riley to be correlated with their luminosity. We revisit this canonical relationship with a sample of 5805 extended radio-loud AGN from the LOFAR Two-Metre Sky Survey (LoTSS), compiling the most complete dataset of radio-galaxy morphological information obtained to date. We demonstrate that, for this sample, radio luminosity does *not* reliably predict whether a source is edge-brightened (FRII) or centre-brightened (FRI). We highlight a large population of low-luminosity FRIIs, extending three orders of magnitude below the traditional FR break, and demonstrate that their host galaxies are on average systematically fainter than those of high-luminosity FRIIs and of FRIs matched in luminosity. This result supports the jet power/environment paradigm for the FR break: low-power jets may remain undisrupted and form hotspots in lower mass hosts. We also find substantial populations that appear physically distinct from the traditional FR classes, including candidate restarting sources and ``hybrids''. We identify 459 bent-tailed sources, which we find to have a significantly higher SDSS cluster association fraction (at $z<0.4$) than the general radio-galaxy population, similar to the results of previous work. The complexity of the LoTSS faint, extended radio sources demonstrates the need for caution in the automated classification and interpretation of extended sources in modern radio surveys, but also reveals the wealth of morphological information such surveys will provide and its value for advancing our physical understanding of radio-loud AGN. △ Less

Submitted 8 July, 2019; originally announced July 2019.

Comments: 21 pages, 4 tables, 16 Figures. Accepted for publication on Monthly Notices of the Royal Astronomical Society (MNRAS). Our LoTSS morphological catalogue containing classifications for 5805 extended radio-loud AGN is available from www.lofar-surveys.org/releases.html

Morphological classification of radio galaxies: Capsule Networks versus Convolutional Neural Networks

Authors: V. Lukic, M. Brüggen, B. Mingo, J. H. Croston, G. Kasieczka, P. N. Best

Abstract: Next-generation radio surveys will yield an unprecedented amount of data, warranting analysis by use of machine learning techniques. Convolutional neural networks are the deep learning technique that has proven to be the most successful in classifying image data. Capsule networks are a more recently developed technique that use capsules comprised of groups of neurons, that describe properties of a… ▽ More Next-generation radio surveys will yield an unprecedented amount of data, warranting analysis by use of machine learning techniques. Convolutional neural networks are the deep learning technique that has proven to be the most successful in classifying image data. Capsule networks are a more recently developed technique that use capsules comprised of groups of neurons, that describe properties of an image including the relative spatial locations of features. The current work explores the performance of different capsule network architectures against simpler convolutional neural network architectures, in reproducing the classifications into the classes of unresolved, FRI and FRII morphologies. We utilise images from a LOFAR survey which is the deepest, wide-area radio survey to date, revealing more complex radio-source structures compared to previous surveys, presenting further challenges for machine learning algorithms. The 4- and 8-layer convolutional networks attain an average precision of 93.3% and 94.3% respectively, compared to 89.7% obtained with the capsule network, when training on original and augmented images. Implementing transfer learning achieves a precision of 94.4%, that is within the confidence interval of the 8-layer convolutional network. The convolutional networks always outperform any variation of the capsule network, as they prove to be more robust to the presence of noise in images. The use of pooling appears to allow more freedom for the intra-class variability of radio galaxy morphologies, as well as reducing the impact of noise. △ Less

Submitted 8 May, 2019; originally announced May 2019.

Comments: 17 pages, 11 figures, Accepted for publication in MNRAS

Cosmic evolution of supermassive black holes: A view into the next two decades

Authors: Francesca Civano, Nico Cappelluti, Ryan Hickox, Rebecca Canning, James Aird, Marco Ajello, Steve Allen, Eduardo Bañados, Laura Blecha, William N. Brandt, Marcella Brusa, Francisco Carrera, Massimo Cappi, Andrea Comastri, Klaus Dolag, Megan Donahue, Martin Elvis, Giuseppina Fabbiano, Francesca Fornasini, Poshak Gandhi, Antonis Georgakakis, Kelly Holley-Bockelmann, Anton Koekemoer, Andrew Goulding, Mackenzie Jones , et al. (16 additional authors not shown)

Abstract: The discoveries made over the past 20 years by Chandra and XMM-Newton surveys in conjunction with multiwavelength imaging and spectroscopic data available in the same fields have significantly changed the view of the supermassive black hole (SMBH) and galaxy connection. These discoveries have opened up several exciting questions that are beyond the capabilities of current X-ray telescopes and will… ▽ More The discoveries made over the past 20 years by Chandra and XMM-Newton surveys in conjunction with multiwavelength imaging and spectroscopic data available in the same fields have significantly changed the view of the supermassive black hole (SMBH) and galaxy connection. These discoveries have opened up several exciting questions that are beyond the capabilities of current X-ray telescopes and will need to be addressed by observatories in the next two decades. As new observatories peer into the early Universe, we will begin to understand the physics and demographics of SMBH infancy (at $z>6$) and investigate the influence of their accretion on the formation of the first galaxies ($§$ 2.1). We will also be able to understand the accretion and evolution over the cosmic history (at $z\sim$1-6) of the full population of black holes in galaxies, including low accretion rate, heavily obscured AGNs at luminosities beyond the reach of current X-ray surveys ($§$2.2 and $§$2.3), enabling us to resolve the connection between SMBH growth and their environment. △ Less

Submitted 26 March, 2019; originally announced March 2019.

Comments: 5 pages, 3 figures; Science white paper submitted to the Astro2020 Decadal Survey

LoTSS DR1: Double-double radio galaxies in the HETDEX field

Authors: V. H. Mahatma, M. J. Hardcastle, W. L. Williams, P. N. Best, J. H. Croston, K. Duncan, B. Mingo, R. Morganti, M. Brienza, R. K. Cochrane, G. Gürkan, J. J. Harwood, M. J. Jarvis, M. Jamrozy, N. Jurlin, L. K. Morabito, H. J. A. Röttgering, J. Sabater, T. W. Shimwell, D. J. B. Smith, A. Shulevski, C. Tasse

Abstract: Double-double radio galaxies (DDRGs) represent a short but unique phase in the life-cycle of some of the most powerful radio-loud active galactic nuclei (RLAGN). These galaxies display large-scale remnant radio plasma in the intergalactic medium left behind by a past episode of active galactic nuclei (AGN) activity, and meanwhile, the radio jets have restarted in a new episode. The knowledge of wh… ▽ More Double-double radio galaxies (DDRGs) represent a short but unique phase in the life-cycle of some of the most powerful radio-loud active galactic nuclei (RLAGN). These galaxies display large-scale remnant radio plasma in the intergalactic medium left behind by a past episode of active galactic nuclei (AGN) activity, and meanwhile, the radio jets have restarted in a new episode. The knowledge of what causes the jets to switch off and restart is crucial to our understanding of galaxy evolution, while it is important to know if DDRGs form a host galaxy dichotomy relative to RLAGN. We utilised the LOFAR Two-Metre Sky Survey DR1, using a visual identification method to compile a sample of morphologically selected candidate DDRGs, showing two pairs of radio lobes. To confirm the restarted nature in each of the candidate sources, we obtained follow-up observations with the VLA at higher resolution to observe the inner lobes or restarted jets, the confirmation of which created a robust sample of 33 DDRGs. We created a comparison sample of 777 RLAGN from the DR1 catalogue, and compared the optical and infrared magnitudes and colours of their host galaxies. We find that there is no statistically significant difference in the brightness of the host galaxies between double-doubles and single-cycle RLAGN. The DDRG and RLAGN samples also have similar distributions in WISE mid-infrared colours, indicating similar ages of stellar populations and dust levels in the hosts of DDRGs. We conclude that DDRGs and 'normal' RLAGN are hosted by galaxies of the same type, and that DDRG activity is simply a normal part of the life cycle of RLAGN. Restarted jets, particularly for the class of low-excitation radio galaxies, rather than being a product of a particular event in the life of a host galaxy, must instead be caused by smaller scale changes, such as in the accretion system surrounding the black hole. △ Less

Submitted 20 November, 2018; originally announced November 2018.

Comments: 20 pages, 2 tables, 54 figures. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal

The environments of radio-loud AGN from the LOFAR Two-Metre Sky Survey (LoTSS)

Authors: J. H. Croston, M. J. Hardcastle, B. Mingo, P. N. Best, J. Sabater, T. W. Shimwell, W. L. Williams, K. J. Duncan, H. J. A. Röttgering, M. Brienza, G. Gürkan, J. Ineson, L. M. Morabito, G. K. Miley, S. P. O'Sullivan, I. Prandoni

Abstract: An understanding of the relationship between radio-loud active galaxies and their large-scale environments is essential for realistic modelling of radio-galaxy evolution and environmental impact, for understanding AGN triggering and life cycles, and for calibrating galaxy feedback in cosmological models. We use the LOFAR Two-Metre Sky Survey (LoTSS) Data Release 1 catalogues to investigate this re… ▽ More An understanding of the relationship between radio-loud active galaxies and their large-scale environments is essential for realistic modelling of radio-galaxy evolution and environmental impact, for understanding AGN triggering and life cycles, and for calibrating galaxy feedback in cosmological models. We use the LOFAR Two-Metre Sky Survey (LoTSS) Data Release 1 catalogues to investigate this relationship. We cross-matched 8,745 radio-loud AGN with 0.08<z<0.4, selected from LoTSS, with two Sloan Digital Sky Survey cluster catalogues, and find that only 10 percent of LoTSS AGN in this redshift range have an association, so that the majority of low-redshift AGN (including a substantial fraction of the most radio-luminous objects) must inhabit haloes with M < 10^14 M_sun. We find that the probability of a cluster association, and the richness of the associated cluster, is correlated with AGN radio luminosity, and for the cluster population, the number of associated AGN and the radio luminosity of the brightest associated AGN is richness-dependent. We demonstrate that these relations are not driven solely by host-galaxy stellar mass, supporting models in which large-scale environment is influential in driving AGN jet activity. At the lowest radio luminosities we find that the minority of objects with a cluster association are located at larger mean cluster-centre distances than more luminous AGN, which appears to be driven primarily by host-galaxy mass. Finally, we also find that FRI radio galaxies inhabit systematically richer environments than FRIIs. The work presented here demonstrates the potential of LoTSS for AGN environmental studies. In future, the full northern-sky LoTSS catalogue, together with the use of deeper optical/IR imaging data and spectroscopic follow-up with WEAVE-LOFAR, will provide opportunities to extend this type of work to much larger samples and higher redshifts. △ Less

Submitted 19 November, 2018; originally announced November 2018.

Comments: 13 pages, 7 figures. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal

Radio-loud AGN in the first LoTSS data release: The lifetimes and environmental impact of jet-driven sources

Authors: M. J. Hardcastle, W. L. Williams, P. N. Best, J. H. Croston, K. J. Duncan, H. J. A. Rottgering, J. Sabater, T. W. Shimwell, C. Tasse, J. R. Callingham, R. K. Cochrane, F. de Gasperin, G. Gurkan, M. J. Jarvis, V. Mahatma, G. K. Miley, B. Mingo, S. Mooney, L. K. Morabito, S. P. O'Sullivan, I. Prandoni, A. Shulevski, D. J. B. Smith

Abstract: We constructed a sample of 23,344 radio-loud active galactic nuclei (RLAGN) from the catalogue derived from the LOFAR Two-Metre Sky Survey (LoTSS) survey of the HETDEX Spring field. Although separating AGN from star-forming galaxies remains challenging, the combination of spectroscopic and photometric techniques we used gives us one of the largest available samples of candidate RLAGN. We used the… ▽ More We constructed a sample of 23,344 radio-loud active galactic nuclei (RLAGN) from the catalogue derived from the LOFAR Two-Metre Sky Survey (LoTSS) survey of the HETDEX Spring field. Although separating AGN from star-forming galaxies remains challenging, the combination of spectroscopic and photometric techniques we used gives us one of the largest available samples of candidate RLAGN. We used the sample, combined with recently developed analytical models, to investigate the lifetime distribution of RLAGN. We show that large or giant powerful RLAGN are probably the old tail of the general RLAGN population, but that the low-luminosity RLAGN candidates in our sample, many of which have sizes $<100$ kpc, either require a very different lifetime distribution or have different jet physics from the more powerful objects. We then used analytical models to develop a method of estimating jet kinetic powers for our candidate objects and constructed a jet kinetic luminosity function based on these estimates. These values can be compared to observational quantities, such as the integrated radiative luminosity of groups and clusters, and to the predictions from models of RLAGN feedback in galaxy formation and evolution. In particular, we show that RLAGN in the local Universe are able to supply all the energy required per comoving unit volume to counterbalance X-ray radiative losses from groups and clusters and thus prevent the hot gas from cooling. Our computation of the kinetic luminosity density of local RLAGN is in good agreement with other recent observational estimates and with models of galaxy formation. △ Less

Submitted 19 November, 2018; originally announced November 2018.

Comments: 21 pages, 11 colour figures. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available at https://lofar-surveys.org/ upon publication of the journal

LoTSS/HETDEX: Optical quasars I. Low-frequency radio properties of optically selected quasars

Authors: Gülay Gürkan, Martin Hardcastle, Philip Best, Leah Morabito, Isabella Prandoni, Matt Jarvis, Ken Duncan, Gabriela Calistro Rivera, Joe Callingham, Rachel Cochrane, Judith Croston, George Heald, Beatriz Mingo, Sean Mooney, Jose Sabater, Huub Röttgering, Timothy Shimwell, Dan Smith, Cyril Tasse, Wendy Williams

Abstract: The radio-loud/radio-quiet (RL/RQ) dichotomy in quasars is still an open question. Although it is thought that accretion onto supermassive black holes in the centre the host galaxies of quasars is responsible for some radio continuum emission, there is still a debate as to whether star formation or active galactic nuclei (AGN) activity dominate the radio continuum luminosity. To date, radio emissi… ▽ More The radio-loud/radio-quiet (RL/RQ) dichotomy in quasars is still an open question. Although it is thought that accretion onto supermassive black holes in the centre the host galaxies of quasars is responsible for some radio continuum emission, there is still a debate as to whether star formation or active galactic nuclei (AGN) activity dominate the radio continuum luminosity. To date, radio emission in quasars has been investigated almost exclusively using high-frequency observations in which the Doppler boosting might have an important effect on the measured radio luminosity, whereas extended structures, best observed at low radio frequencies, are not affected by the Doppler enhancement. We used a sample of quasars selected by their optical spectra in conjunction with sensitive and high-resolution low-frequency radio data provided by the LOw Frequency ARray (LOFAR) as part of the LOFAR Two-Metre Sky Survey (LoTSS) to investigate their radio properties using the radio loudness parameter ($\mathcal{R} = \frac{L_{\mathrm{144-MHz}}}{L_{\mathrm{i\,band}}}$). The examination of the radio continuum emission and RL/RQ dichotomy in quasars exhibits that quasars show a wide continuum of radio properties (i.e. no clear bimodality in the distribution of $\mathcal{R}$). Radio continuum emission at low frequencies in low-luminosity quasars is consistent with being dominated by star formation. We see a significant albeit weak dependency of $\mathcal{R}$ on the source nuclear parameters. For the first time, we are able to resolve radio morphologies of a considerable number of quasars. All these crucial results highlight the impact of the deep and high-resolution low-frequency radio surveys that foreshadow the compelling science cases for the Square Kilometre Array (SKA). △ Less

Submitted 19 November, 2018; originally announced November 2018.

Comments: 16 pages, 12 figures, 4 tables. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal

The LOFAR Two-metre Sky Survey IV. First Data Release: Photometric redshifts and rest-frame magnitudes

Authors: Kenneth J Duncan, J. Sabater, H. J. A. Röttgering, M. J. Jarvis, D. J. B. Smith, P. N. Best, J. R. Callingham, R. Cochrane, J. H. Croston, M. J. Hardcastle, B. Mingo, L. Morabito, D. Nisbet, I. Prandoni, T. W. Shimwell, C. Tasse, G. J. White, W. L. Williams, L. Alegre, K. T. Chyży, G. Gürkan, M. Hoeft, R. Kondapally, A. P. Mechev, G. K. Miley , et al. (2 additional authors not shown)

Abstract: The LOFAR Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120-168 MHz survey of the Northern sky. The LoTSS First Data Release (DR1) presents 424 square degrees of radio continuum observations over the HETDEX Spring Field (10h45m00s $<$ right ascension $<$ 15h30m00s and 45$^\circ$00$'$00$'$ $<$ declination $<$ 57$^\circ$00$'$00$''$) with a median sensitivity of 71$μ$Jy/beam and a reso… ▽ More The LOFAR Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120-168 MHz survey of the Northern sky. The LoTSS First Data Release (DR1) presents 424 square degrees of radio continuum observations over the HETDEX Spring Field (10h45m00s $<$ right ascension $<$ 15h30m00s and 45$^\circ$00$'$00$'$ $<$ declination $<$ 57$^\circ$00$'$00$''$) with a median sensitivity of 71$μ$Jy/beam and a resolution of 6$''$. In this paper we present photometric redshifts (photo-$z$) for 94.4% of optical sources over this region that are detected in the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) 3$π$ steradian survey. Combining the Pan-STARRS optical data with mid-infrared photometry from the Wide-field Infrared Survey Explorer, we estimate photo-$z$s using a novel hybrid photometric redshift methodology optimised to produce the best possible performance for the diverse sample of radio continuum selected sources. For the radio-continuum detected population, we find an overall scatter in the photo-$z$ of 3.9% and an outlier fraction ($\left | z_{\rm{phot}} - z_{\rm{spec}} \right | / (1+z_{\rm{spec}}) > 0.15$) of 7.9%. We also find that, at a given redshift, there is no strong trend in photo-$z$ quality as a function of radio luminosity. However there are strong trends as a function of redshift for a given radio luminosity, a result of selection effects in the spectroscopic sample and/or intrinsic evolution within the radio source population. Additionally, for the sample of sources in the LoTSS First Data Release with optical counterparts, we present rest-frame optical and mid-infrared magnitudes based on template fits to the consensus photometric (or spectroscopic when available) redshift. △ Less

Submitted 19 November, 2018; originally announced November 2018.

Comments: 16 figures, 1 table and 18 pages. This paper is part of the LOFAR surveys Data Release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, Volume 622. The catalogues and images from the data release will be publicly available at http://www.lofar-surveys.org upon publication of the volume

The LOFAR Two-metre Sky Survey (LoTSS) III. First Data Release: optical/IR identifications and value-added catalogue

Authors: W. L. Williams, M. J. Hardcastle, P. N. Best, J. Sabater, J. H. Croston, K. J. Duncan, T. W. Shimwell, H. J. A. Röttgering, D. Nisbet, G. Gürkan, L. Alegre, R. K. Cochrane, A. Goyal, C. L. Hale, N. Jackson, M. Jamrozy, R. Kondapally, M. Kunert-Bajraszewska, V. H. Mahatma, B. Mingo, L. K. Morabito, I. Prandoni, C. Roskowinski, A. Shulevski, D. J. B. Smith , et al. (16 additional authors not shown)

Abstract: The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168 MHz survey of the Northern sky with diverse and ambitious science goals. Many of the scientific objectives of LoTSS rely upon, or are enhanced by, the association or separation of the sometimes incorrectly catalogued radio components into distinct radio sources, and the identification and characterisation of th… ▽ More The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168 MHz survey of the Northern sky with diverse and ambitious science goals. Many of the scientific objectives of LoTSS rely upon, or are enhanced by, the association or separation of the sometimes incorrectly catalogued radio components into distinct radio sources, and the identification and characterisation of the optical counterparts to these sources. Here we present the source associations and optical and/or IR identifications for sources in the first data release, which are made using a combination of statistical techniques and visual association and identification. We document in detail the colour- and magnitude-dependent likelihood ratio method used for statistical identification as well as the Zooniverse project, called LOFAR Galaxy Zoo, used for the visual classification. We describe the process used to select which of these two different methods is most appropriate for each LoTSS source. The final LoTSS-DR1-IDs value-added catalogue presented contains 318,520 radio sources, of which 231,716 (73%) have optical and/or IR identifications in Pan-STARRS and WISE. The value-added catalogue is available online at https://lofar-surveys.org/, as part of this data release. △ Less

Submitted 19 November, 2018; originally announced November 2018.

Comments: 8 figures, 5 tables and 23 pages. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available at https://lofar-surveys.org/ upon publication in the journal

Journal ref: A&A 622, A2 (2019)