Search

The aim of this study is to probe the sub-mJy polarized source population with LOFAR. We present the method used to stack LOFAR polarization datasets, the resulting catalog of polarized sources, and the derived polarized source counts. The ELAIS-N1 field was selected for a polarimetric study at 114.9-177.4 MHz. A total area of 25 deg2 was imaged at 6"- resolution in the Stokes Q and U parameters. Alignment of polarization angles was done both in frequency and in Faraday space before stacking datasets from 19 eight-hour-long epochs. A search for polarized sources was carried out in the final, stacked dataset, and the properties of the detected sources were examined. The depolarization level of sources known to be polarized at 1.4 GHz was quantified. A one-sigma noise level of 19 {\mu}Jy/beam was reached in the central part of the field after stacking. Twenty-five polarized sources were detected above 8\sigma, five of which had not been detected in polarization at any other radio frequencies before. Seven additional polarized components were found by lowering the threshold to 6\sigma at positions corresponding to sources known to be polarized at 1.4 GHz. In two radio galaxies, polarization was detected from both radio lobes, so the final number of associated radio continuum sources is 31. The detected sources are weakly polarized, with a median degree of polarization of 1.75% for the sample of sources detected in polarized emission. The sources previously detected in polarization at 1.4 GHz are significantly depolarized at 150 MHz. The catalog is used to derive the polarized source counts at 150 MHz. This is the deepest and highest-resolution polarization study at 150 MHz to date., Comment: 18 pages, 10 figures, accepted for publication in A&A

The second data release of the LOFAR Two-Metre Sky Survey (LoTSS) covers 27% of the northern sky, with a total area of $\sim 5,700$ deg$^2$. The high angular resolution of LOFAR with Dutch baselines (6 arcsec) allows us to carry out optical identifications of a large fraction of the detected radio sources without further radio followup; however, the process is made more challenging by the many extended radio sources found in LOFAR images as a result of its excellent sensitivity to extended structure. In this paper we present source associations and identifications for sources in the second data release based on optical and near-infrared data, using a combination of a likelihood-ratio cross-match method developed for our first data release, our citizen science project Radio Galaxy Zoo: LOFAR, and new approaches to algorithmic optical identification, together with extensive visual inspection by astronomers. We also present spectroscopic or photometric redshifts for a large fraction of the optical identifications. In total 4,116,934 radio sources lie in the area with good optical data, of which 85% have an optical or infrared identification and 58% have a good redshift estimate. We demonstrate the quality of the dataset by comparing it with earlier optically identified radio surveys. This is by far the largest ever optically identified radio catalogue, and will permit robust statistical studies of star-forming and radio-loud active galaxies., Comment: 29 pages. Accepted by A&A; data products available at https://lofar-surveys.org/dr2_release.html

Extragalactic radio continuum surveys play an increasingly more important role in galaxy evolution and cosmology studies. While radio galaxies and radio quasars dominate at the bright end, star-forming galaxies (SFGs) and radio-quiet Active Galactic Nuclei (AGNs) are more common at fainter flux densities. Our aim is to develop a machine learning classifier that can efficiently and reliably separate AGNs and SFGs in radio continuum surveys. We perform supervised classification of SFGs vs AGNs using the Light Gradient Boosting Machine (LGBM) on three LOFAR Deep Fields (Lockman Hole, Bootes and ELAIS-N1), which benefit from a wide range of high-quality multi-wavelength data and classification labels derived from extensive spectral energy distribution (SED) analyses. Our trained model has a precision of 0.92(0.01) and a recall of 0.87(0.02) for SFGs. For AGNs, the model has slightly worse performance, with a precision of 0.87(0.02) and recall of 0.78(0.02). These results demonstrate that our trained model can successfully reproduce the classification labels derived from detailed SED analysis. The model performance decreases towards higher redshifts, mainly due to smaller training sample sizes. To make the classifier more adaptable to other radio galaxy surveys, we also investigate how our classifier performs with a poorer multi-wavelength sampling of the SED. In particular, we find that the far-infrared (FIR) and radio bands are of great importance. We also find that higher S/N in some photometric bands leads to a significant boost in the model's performance. In addition to using the 150 MHz radio data, our model can also be used with 1.4 GHz radio data. Converting 1.4 GHz to 150 MHz radio data reduces performance by about 4% in precision and 3% in recall. The final trained model is publicly available at https://github.com/Jesper-Karsten/MBASC, Comment: 14 pages 9 figures Accepted for publication in A&A

We present a detailed study of the cosmic star formation history over $90$ per cent of cosmic time ($0\lesssim z\lesssim4$), using deep, radio continuum observations that probe star formation activity independent of dust. The Low Frequency Array Two Metre Sky Survey has imaged three well-studied extragalactic fields, Elais-N1, Bo\"otes and the Lockman Hole, reaching $\sim20\,\mu\rm{Jy/beam}$ rms sensitivity at $150\,\rm{MHz}$. The availability of high-quality ancillary data from ultraviolet to far-infrared wavelengths has enabled accurate photometric redshifts and the robust separation of radio-bright AGN from their star-forming counterparts. We capitalise on this unique combination of deep, wide fields and robustly-selected star-forming galaxies to construct radio luminosity functions and derive the cosmic star formation rate density. We carefully constrain and correct for scatter in the $L_{150\,\rm{MHz}}-\rm{SFR}$ relation, which we find to be $\sim0.3\,\rm{dex}$. Our derived star formation rate density lies between previous measurements at all redshifts studied. We derive higher star formation rate densities between $z\sim0$ and $z\sim3$ than are typically inferred from short wavelength emission; at earlier times, this discrepancy is reduced. Our measurements are generally in good agreement with far-infrared and radio-based studies, with small offsets resulting from differing star formation rate calibrations., Comment: 22 pages, 14 figures; accepted for publication in MNRAS

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

The Square Kilometre Array Observatory (SKAO) will explore the radio sky to new depths in order to conduct transformational science. SKAO data products made available to astronomers will be correspondingly large and complex, requiring the application of advanced analysis techniques to extract key science findings. To this end, SKAO is conducting a series of Science Data Challenges, each designed to familiarise the scientific community with SKAO data and to drive the development of new analysis techniques. We present the results from Science Data Challenge 2 (SDC2), which invited participants to find and characterise 233245 neutral hydrogen (Hi) sources in a simulated data product representing a 2000~h SKA MID spectral line observation from redshifts 0.25 to 0.5. Through the generous support of eight international supercomputing facilities, participants were able to undertake the Challenge using dedicated computational resources. Alongside the main challenge, `reproducibility awards' were made in recognition of those pipelines which demonstrated Open Science best practice. The Challenge saw over 100 participants develop a range of new and existing techniques, with results that highlight the strengths of multidisciplinary and collaborative effort. The winning strategy -- which combined predictions from two independent machine learning techniques to yield a 20 percent improvement in overall performance -- underscores one of the main Challenge outcomes: that of method complementarity. It is likely that the combination of methods in a so-called ensemble approach will be key to exploiting very large astronomical datasets., Comment: Under review by MNRAS; 28 pages, 16 figures

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., Comment: 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

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$00' and spanning 4178 and 1457 square degrees respectively. The images were derived from 3,451hrs (7.6PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4,396,228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 6" resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144MHz have: a median rms sensitivity of 83$\mu$Jy/beam; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.2"; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8mJy/beam. By creating three 16MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of +/-0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 20" resolution 120-168MHz continuum images have a median rms sensitivity of 95$\mu$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., Comment: 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/

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

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., Comment: 16 pages, 7 figures, accepted for publication in MNRAS

Coherent low-frequency ($\lesssim 200$ MHz) radio emission from stars encodes the conditions of the outer corona, mass-ejection events, and space weather. Previous low-frequency searches for radio emitting stellar systems have lacked the sensitivity to detect the general population, instead largely focusing on targeted studies of anomalously active stars. Here we present 19 detections of coherent radio emission associated with known M~dwarfs from a blind flux-limited low-frequency survey. Our detections show that coherent radio emission is ubiquitous across the M~dwarf main sequence, and that the radio luminosity is independent of known coronal and chromospheric activity indicators. While plasma emission can generate the low-frequency emission from the most chromospherically active stars of our sample, the origin of the radio emission from the most quiescent sources is yet to be ascertained. Large-scale analogues of the magnetospheric processes seen in gas-giant planets likely drive the radio emission associated with these quiescent stars. The slowest-rotating stars of this sample are candidate systems to search for star-planet interaction signatures., Comment: Accepted to Nature Astronomy; 31 pages, 9 figures, and 2 tables

We examine the distribution of radio emission from ~42,000 quasars from the Sloan Digital Sky Survey, as measured in the LOFAR Two-Metre Sky Survey (LoTSS). We present a model of the radio luminosity distribution of the quasars that assumes that every quasar displays a superposition of two sources of radio emission: active galactic nuclei (jets) and star-formation. Our two-component model provides an excellent match to the observed radio flux density distributions across a wide range of redshifts and quasar optical luminosities; this suggests that the jet-launching mechanism operates in all quasars but with different powering efficiency. The wide distribution of jet powers allows for a smooth transition between the 'radio-quiet' and 'radio-loud' quasar regimes, without need for any explicit bimodality. The best-fit model parameters indicate that the star-formation rate of quasar host galaxies correlates strongly with quasar luminosity and also increases with redshift at least out to z~2. For a model where star-formation rate scales as $SFR \propto L_{bol}^\alpha (1+z)^\beta$, we find $\alpha = 0.47 \pm 0.01$ and $\beta = 1.61 \pm 0.05$, in agreement with far-infrared studies. Quasars contribute ~0.15 per cent of the cosmic star-formation rate density at z=0.5, rising to 0.4 per cent by z=2. The typical radio jet power is seen to increase with both increasing optical luminosity and black hole mass independently, but does not vary with redshift, suggesting intrinsic properties govern the production of the radio jets. We discuss the implications of these results for the triggering of quasar activity and the launching of jets., Comment: Accepted for publication in MNRAS. 21 pages

We study the radio and optical properties of the brightest group galaxies (BGGs) in a sample of galaxy groups from the SDSS DR7. The luminosity difference between the BGG and the second ranked galaxy in the group (known as the luminosity, or magnitude, gap) has been used as a probe for the level of galaxy interaction for the BGG within the group. We study the properties of BGGs with magnitude gaps in the range 0-2.7 magnitudes, in order to investigate any relation between luminosity gap and the radio properties of the BGG. In order to eliminate selection biases, we ensure that all variations in stellar mass are accounted for. We then confirm that, at fixed stellar mass, there are no significant variations in the optical properties of the BGGs over the full range of luminosity gaps studied. We compare these optical results with the EAGLE hydrodynamical simulations and find broad consistency with the observational data. Using EAGLE we also confirm that no trends begin to arise in the simulated data at luminosity gaps beyond our observational limits. Finally, we find that, at fixed stellar mass, the fraction of BGGs that are radio-loud also shows no trends as a function of luminosity gap. We examine how the BGG offset from the center of group may affect the radio results and find no significant trend for the fraction of radio-loud BGGs with magnitude gap in either the BGG samples with greater or less than 100kpc offset from the center of group., Comment: Accepted for publication in AJ

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

Recently detected coherent low-frequency radio emission from M dwarf systems shares phenomenological similarities with emission produced by magnetospheric processes from the gas giant planets of our Solar System. Such beamed electron-cyclotron maser emission can be driven by a star-planet interaction or a breakdown in co-rotation between a rotating plasma disk and a stellar magnetosphere. Both models suggest that the radio emission could be periodic. Here we present the longest low-frequency interferometric monitoring campaign of an M dwarf system, composed of twenty-one $\approx$8 hour epochs taken in two series of observing blocks separated by a year. We achieved a total on-source time of 6.5 days. We show that the M dwarf binary CR Draconis has a low-frequency 3$\sigma$ detection rate of 90$^{+5}_{-8}$% when a noise floor of $\approx$0.1 mJy is reached, with a median flux density of 0.92 mJy, consistent circularly polarised handedness, and a median circularly polarised fraction of 66%. We resolve three bright radio bursts in dynamic spectra, revealing the brightest is elliptically polarised, confined to 4 MHz of bandwidth centred on 170 MHz, and reaches a flux density of 205 mJy. The burst structure is mottled, indicating it consists of unresolved sub-bursts. Such a structure shares a striking resemblance with the low-frequency emission from Jupiter. We suggest the near-constant detection of high brightness temperature, highly-circularly-polarised radiation that has a consistent circular polarisation handedness implies the emission is produced via the electron-cyclotron maser instability. Optical photometric data reveal the system has a rotation period of 1.984$\pm$0.003 days. We observe no periodicity in the radio data, but the sampling of our radio observations produces a window function that would hide the near two-day signal., Comment: Accepted for publication in A&A, 16 pages, 7 figures, 2 tables

We provide the most accurate estimate yet of the bright end of the infrared (IR) luminosity functions (LFs) and the abundance of hyperluminous IR galaxies (HLIRGs) with IR luminosities > 10^13 L_solar, thanks to the combination of the high sensitivity, angular resolution, and large area of the LOFAR Deep Fields, which probes an unprecedented dynamic range of luminosity and volume. We cross-match Herschel sources and LOFAR sources in Bootes (8.63 deg^2), Lockman Hole (10.28 deg^2), and ELAIS-N1 (6.74 deg^2) with rms sensitivities of around 32, 22, and 20 mJy per beam, respectively. We divide the matched samples into unique and multiple categories. For the multiple matches, we de-blend the Herschel fluxes using the LOFAR positions and the 150-MHz flux densities as priors. We perform spectral energy distribution (SED) fitting, combined with multi-wavelength counterpart identifications and photometric redshift estimates, to derive IR luminosities. The depth of the LOFAR data allows us to identify highly complete (around 92% completeness) samples of bright Herschel sources with a simple selection based on the 250 micron flux density (45, 40, and 35 mJy in Bootes, Lockman Hole, and ELAIS-N1, respectively). Most of the bright Herschel sources fall into the unique category (i.e. a single LOFAR counterpart). For the multiple matches, there is excellent correspondence between the radio emission and the far-IR emission. We find a good agreement in the IR LFs with a previous study out to z around 6 which used de-blended Herschel data. Our sample gives the strongest and cleanest indication to date that the population of HLIRGs has surface densities of around 5 to 18 / deg^2 (with variations due to a combination of the applied flux limit and cosmic variance) and an uncertainty of a factor of 2. In comparison, the GALFORM semi-analytic model significantly under-predicts the abundance of HLIRGs., Comment: 16 pages, 11 figures, accepted for publication in A&A as part of the LOFAR Deep Fields Paper Splash

With the advent of new generation low-frequency telescopes, such as the LOw Frequency ARray (LOFAR), and improved calibration techniques, we have now started to unveil the sub GHz radio sky with unprecedented depth and sensitivity. The LOFAR Two Meter Sky Survey (LoTSS) is an ongoing project in which the whole northern radio sky will be observed at 150 MHz with a sensitivity better than 100 $\mu$Jy beam$^{-1}$ at a resolution of \asec{6}. Additionally, deeper observations are planned to cover smaller areas with higher sensitivity. The Lockman Hole, the Bo\"otes and the Elais-N1 regions are among the most well known northern extra-galactic fields, and the deepest of the LoTSS Deep Fields so far. We exploit these deep observations to derive the deepest radio source counts at 150~MHz to date. Our counts are in broad agreement with those from the literature, and show the well known upturn at $\leq$ few mJy, mainly associated with the emergence of the star-forming galaxy population. More interestingly, our counts show for the first time a very pronounced drop around S$\sim$2 mJy, which results in a prominent `bump' at sub-mJy flux densities. Such a feature was not observed in previous counts' determinations (neither at 150 MHz nor at higher frequency). While sample variance can play a role in explaining the observed discrepancies, we believe this is mostly the result of a careful analysis aimed at deblending confused sources and removing spurious sources and artifacts from the radio catalogues. This `drop and bump' feature cannot be reproduced by any of the existing state-of-the-art evolutionary models, and appears to be associated with a deficiency of AGN at intermediate redshift ($1

The Low Frequency Array (LOFAR) is an ideal instrument to conduct deep extragalactic surveys. It has a large field of view and is sensitive to large scale and compact emission. It is, however, very challenging to synthesize thermal noise limited maps at full resolution, mainly because of the complexity of the low-frequency sky and the direction dependent effects (phased array beams and ionosphere). In this first paper of a series we present a new calibration and imaging pipeline that aims at producing high fidelity, high dynamic range images with LOFAR High Band Antenna data, while being computationally efficient and robust against the absorption of unmodeled radio emission. We apply this calibration and imaging strategy to synthesize deep images of the Bootes and LH fields at 150 MHz, totaling $\sim80$ and $\sim100$ hours of integration respectively and reaching unprecedented noise levels at these low frequencies of $\lesssim30$ and $\lesssim23$ $\mu$Jy/beam in the inner $\sim3$ deg$^2$. This approach is also being used to reduce the LoTSS-wide data for the second data release., Comment: This paper is part of the 1st data release of the LoTSS Deep Fields. Electronic data catalogues will be made available on journal publication

In recent years, the level of the extragalactic radio background has become a point of considerable interest, with some lines of argument pointing to an entirely new cosmological synchrotron background. The contribution of the known discrete source population to the sky temperature is key to this discussion. Because of the steep spectral index of the excess over the cosmic microwave background, it is best studied at low frequencies where the signal is strongest. The Low-Frequency Array (LOFAR) wide and deep sky surveys give us the best constraints yet on the contribution of discrete extragalactic sources at 144 MHz, and in particular allow us to include contributions from diffuse, low-surface-brightness emission that could not be fully accounted for in previous work. We show that, even with these new data, known sources can still only account for around a quarter of the estimated extragalactic sky temperature at LOFAR frequencies., Comment: 8 pages, 4 figures. This paper is part of the 1st data release of the LoTSS Deep Fields

We present deep polarimetric observations of the European Large Area ISO Survey-North 1 (ELAIS-N1) field using the Low Frequency Array (LOFAR) at 114.9-177.4 MHz. The ELAIS-N1 field is part of the LOFAR Two-metre Sky Survey deep fields data release I. For six eight-hour observing epochs, we align the polarization angles and stack the 20"-resolution Stokes $Q$, $U$-parameter data cubes. This produces a 16 deg$^2$ image with 1$\sigma_{\rm QU}$ sensitivity of 26 $\mu$Jy/beam in the central area. In this paper, we demonstrate the feasibility of the stacking technique, and we generate a catalog of polarized sources in ELAIS-N1 and their associated Faraday rotation measures (RMs). While in a single-epoch observation we detect three polarized sources, this number increases by a factor of about three when we consider the stacked data, with a total of ten sources. This yields a surface density of polarized sources of one per 1.6 deg$^2$. The Stokes $I$ images of three of the ten detected polarized sources have morphologies resembling those of FR I radio galaxies. This represents a greater fraction of this type of source than previously found, which suggests that more sensitive observations may help with their detection., Comment: This paper is part of the 1st data release of the LoTSS Deep Fields. Accepted for publication in A&A. 14 pages, 9 figures, 7 tables

Low-frequency radio observations are revealing an increasing number of diffuse synchrotron sources from galaxy clusters, dominantly in the form of radio halos or radio relics. The existence of this diffuse synchrotron emission indicates the presence of relativistic particles and magnetic fields. It is still an open question what mechanisms exactly are responsible for the population of relativistic electrons driving this synchrotron emission. The LOFAR Two-metre Sky Survey Deep Fields offer a unique view of this problem. Reaching noise levels below 30 $\mu$Jy/beam, these are the deepest images made at the low frequency of 144 MHz. This paper presents a search for diffuse emission in galaxy clusters in the first data release of the LOFAR Deep Fields. We detect a new high-redshift radio halo with a flux density of $8.9 \pm 1.0$ mJy and corresponding luminosity of $P_{144\mathrm{MHz}}=(3.6 \pm 0.6)\times10^{25}$ W Hz$^{-1}$ in an X-ray detected cluster at $z=0.77$ with a mass estimate of $M_{500} = 3.3_{-1.7}^{+1.1} \times 10^{14} M_\odot.$ Deep upper limits are placed on clusters with non-detections. We compare the results to the correlation between halo luminosity and cluster mass derived for radio halos found in the literature. This study is one of few to find diffuse emission in low mass ($M_{500} < 5\times10^{14} M_\odot$) systems and shows that deep low-frequency observations of galaxy clusters are fundamental for opening up a new part of parameter space in the study of non-thermal phenomena in galaxy clusters., Comment: This paper is part of the 1st data release of the LoTSS Deep Fields. Re-submitted paper (reply to referee)

The LOFAR Two-metre Sky Survey (LoTSS) will cover the full northern sky and, additionally, aims to observe the LoTSS deep fields to a noise level of ~10 microJy/bm over several tens of square degrees in areas that have the most extensive ancillary data. This paper presents the ELAIS-N1 deep field, the deepest of the LoTSS deep fields to date. With an effective observing time of 163.7 hours, it reaches a root mean square (RMS) noise level below 20 microJy/bm in the central region (and below 30 microJy/bm over 10 square degrees). The resolution is 6 arcsecs and 84862 radio sources were detected in the full area (68 sq. deg.) with 74127 sources in the highest quality area at less than 3 degrees from the pointing centre. The observation reaches a sky density of more than 5000 sources per sq. deg. in the central ~5 sq. deg. region. We present the calibration procedure, which addresses the special configuration of some observations and the extended bandwidth covered (115 to 177 MHz; central frequency 146.2 MHz) compared to standard LoTSS. We also describe the methods used to calibrate the flux density scale using cross-matching with sources detected by other radio surveys in the literature. We find the flux density uncertainty related to the flux density scale to be ~6.5%. By studying the variations of the flux density measurements between different epochs, we show that relative flux density calibration is reliable out to about a 3 degree radius, but that additional flux density uncertainty is present for all sources at about the 3 per cent level; this is likely to be associated with residual calibration errors, and is shown to be more significant in datasets with poorer ionosphere conditions. We also provide intra-band spectral indices, which can be useful to detect sources with unusual spectral properties. The final uncertainty in the flux densities is estimated to be ~10% for ELAIS-N1., Comment: Accepted for publication in A&A. This paper is part of the 1st data release of the LoTSS Deep Fields. Electronic data catalogues will be made available on journal publication. 21 pages, 17 figures

Lyman alpha emitters (LAEs) in the Epoch of Reionization (EoR) offer valuable probes of early galaxy evolution and the process of reionization; however, the exact evolution of their abundance and the nature of their emission remain open questions. We combine samples of 229 and 349 LAE candidates at $z=5.7$ and $z=6.6,$ respectively, from the SILVERRUSH narrowband survey with deep Low Frequency Array (LOFAR) radio continuum observations in the ELAIS-N1 field to search for radio galaxies in the EoR and study the low-frequency radio properties of $z\gtrsim5.7$ LAE emitters. Our LOFAR observations reach an unprecedented noise level of $\sim20\,\mu$Jy beam$^{-1}$ at 150MHz, and we detect five candidate LAEs at $>5\sigma$ significance. Based on detailed spectral energy distribution modelling of independent multi-wavelength observations, we conclude that these sources are likely [OII] emitters at $z=1.47$, yielding no reliable $z\gtrsim5.7$ radio galaxy candidates. We examine the 111 $z=5.7$ and $z=6.6$ LAE candidates from our panchromatic photometry catalogue that are undetected by LOFAR, finding contamination rates of 81-92% for the $z=5.7$ and $z=6.6$ subset of the LAE candidate samples. This subset is biased towards brighter magnitudes and redder near-infrared colours. The contamination rates of the full sample will therefore likely be lower than the reported values. Contamination is lowered significantly through constraints on the near-infrared colours, highlighting the need for infrared observations to robustly identify bright LAEs in narrowband surveys. Finally, the stacking of radio continuum observations for the robust LAE samples yields 2$\sigma$ upper limits on radio luminosity of 8.2$\times$10$^{23}$ and 8.7$\times$10$^{23}$ W Hz$^{-1}$ at $z=5.7$ and $6.6$, respectively, corresponding to limits on their median star-formation rates of $<$53 and $<$56 M$_{\odot}$ yr$^{-1}$., Comment: 17 pages, 11 figures, accepted for publication in A&A. The abstract is abridged. This paper is part of the 1st data release of the LoTSS Deep Fields

The Low Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120-168 MHz survey split across multiple tiers over the northern sky. The first LoTSS Deep Fields data release consists of deep radio continuum imaging at 150 MHz of the Bo\"{o}tes, European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1), and Lockman Hole fields, down to rms sensitivities of $\sim$32, 20, and 22 $\mu$Jy beam$^{-1}$, respectively. In this paper we present consistent photometric redshift (photo-$z$) estimates for the optical source catalogues in all three fields - totalling over 7 million sources ($\sim5$ million after limiting to regions with the best photometric coverage). Our photo-$z$ estimation uses a hybrid methodology that combines template fitting and machine learning and is optimised to produce the best possible performance for the radio continuum selected sources and the wider optical source population. Comparing our results with spectroscopic redshift samples, we find a robust scatter ranging from 1.6 to 2% for galaxies and 6.4 to 7% for identified optical, infrared, or X-ray selected active galactic nuclei (AGN). Our estimated outlier fractions ($\left | z_{\text{phot}} - z_{\text{spec}} \right | / (1+z_{\text{spec}}) > 0.15$) for the corresponding subsets range from 1.5 to 1.8% and 18 to 22%, respectively. Replicating trends seen in analyses of previous wide-area radio surveys, we find no strong trend in photo-$z$ quality as a function of radio luminosity for a fixed redshift. We exploit the broad wavelength coverage available within each field to produce galaxy stellar mass estimates for all optical sources at $z < 1.5$. Stellar mass functions derived for each field are used to validate our mass estimates, with the resulting estimates in good agreement between each field and with published results from the literature., Comment: 23 pages, 14 figures. Accepted for publication in A&A. This paper is part of the 1st data release of the LoTSS Deep Fields - Electronic data catalogues will be made available on journal publication

In this paper, we investigate the relationship between 150MHz luminosity and star formation rate (the SFR-L150 relation) using 150MHz measurements for a near-infrared selected sample of 118,517 $z<1$ galaxies. New radio survey data offer compelling advantages for studying star formation in galaxies, with huge increases in sensitivity, survey speed and resolution over previous generation surveys, and remaining impervious to extinction. The LOFAR Surveys Key Science Project is transforming our understanding of the low-frequency radio sky, with the 150MHz data over the ELAIS-N1 field reaching an RMS sensitivity of 20uJy/beam over 10 deg$^2$ at 6" resolution. All of the galaxies studied have SFR and stellar mass estimates derived from energy balance SED fitting, using redshifts and aperture-matched forced photometry from the LOFAR Two-metre Sky Survey (LoTSS) deep fields data release. The impact of active galactic nuclei is minimised by leveraging the deep ancillary data alongside outlier-resistant median-likelihood methods. We find a linear and non-evolving SFR-L150 relation, apparently consistent with expectations based on calorimetric arguments, down to the lowest SFRs. However, we also recover compelling evidence for stellar mass dependence in line with previous work on this topic, in the sense that higher mass galaxies have a larger 150MHz luminosity at a given SFR, suggesting that the overall agreement with calorimetric arguments may be a coincidence. We conclude that in the absence of AGN, 150MHz observations can be used to measure accurate galaxy SFRs out to $z=1$ at least, but it is necessary to account for stellar mass in order to obtain 150MHz-derived SFRs accurate to <0.5 dex. Our best-fit relation is $\log_{10} (L_\mathrm{150 MHz} / W\,Hz^{-1}) = (0.90\pm 0.01) \log_{10}(\psi/M_\odot\,\mathrm{yr}^{-1}) + (0.33 \pm 0.04) \log_{10} (M/10^{10}M_\odot) + 22.22 \pm 0.02$. (Abridged), Comment: 17 pages, 17 figures, accepted for publication in A&A. This paper is part of the 1st data release of the LoTSS Deep Fields

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 Bo\"{o}tes fields, down to RMS sensitives of around 20, 22, and 32$~\mu$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 Bo\"{o}tes, 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., Comment: 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

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., Comment: 23 pages, accepted by MNRAS

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

Aims. We aim to study the far-infrared radio correlation (FIRC) at 150 MHz in the local Universe (at a median redshift z~0:05) and improve the use of the rest-frame 150-MHz luminosity, L150, as a star-formation rate (SFR) tracer, which is unaffected by dust extinction. Methods. We cross-match the 60-um selected Revised IRAS Faint Source Survey Redshift (RIFSCz) catalogue and the 150-MHz selected LOFAR value-added source catalogue in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Spring Field. We estimate L150 for the cross-matched sources and compare it with the total infrared (IR) luminosity, LIR, and various SFR tracers. Results. We find a tight linear correlation between log L150 and log LIR for star-forming galaxies, with a slope of 1.37. The median qIR value (defined as the logarithm of the LIR to L150 ratio) and its rms scatter of our main sample are 2.14 and 0.34, respectively. We also find that log L150 correlates tightly with the logarithm of SFR derived from three different tracers, i.e., SFR_Halpha based on the Halpha line luminosity, SFR_60 based on the rest-frame 60-um luminosity and SFR_IR based on LIR, with a scatter of 0.3 dex. Our best-fit relations between L150 and these SFR tracers are, log L150 (Lsun) = 1.35(0.06) x log SFR_Halpha (Msun/yr) + 3.20(0.06), log L150 (Lsun) = 1.31(0.05) x log SFR_60 (Msun/yr) + 3.14(0.06), and log L150 (Lsun) = 1.37(0.05) x log SFR_IR (Msun/yr) + 3.09(0.05), which show excellent agreement with each other., Comment: 13 pages, 13 figures, accepted for publication in A&A

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., Comment: 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

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., Comment: 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

We present a study of the low-frequency radio properties of broad absorption line quasars (BALQSOs) from the LOFAR Two-metre Sky-Survey Data Release 1 (LDR1). The value-added LDR1 catalogue contains Pan-STARRS counterparts, which we match with the Sloan Digital Sky Survey (SDSS) DR7 and DR12 quasar catalogues. We find that BALQSOs are twice as likely to be detected at 144$\,$MHz than their non-BAL counterparts, and BALQSOs with low-ionisation species present in their spectra are three times more likely to be detected than those with only high-ionisation species. The BALQSO fraction at 144$\,$MHz is constant with increasing radio luminosity, which is inconsistent with previous results at 1.4$\,$GHz, indicating that observations at the different frequencies may be tracing different sources of radio emission. We cross-match radio sources between the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey and LDR1, which provides a bridge via the LDR1 Pan-STARRS counterparts to identify BALQSOs in SDSS. Consequently we expand the sample of BALQSOs detected in FIRST by a factor of three. The LDR1-detected BALQSOs in our sample are almost exclusively radio-quiet (\logr $\,<2$), with radio sizes at 144$\,$MHz typically less than $200\,$kpc; these radio sizes tend to be larger than those at 1.4$\,$GHz, suggesting more extended radio emission at low frequencies. We find that although the radio detection fraction increases with increasing balnicity index (BI), there is no correlation between BI and either low-frequency radio power or radio-loudness. This suggests that both radio emission and BI may be linked to the same underlying process, but are spatially distinct phenomena., Comment: 16 figures, 3 tables and 19 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 on lofar-surveys.org upon publication of the journal

The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45$^\circ$00$'$00$''$ to 57$^\circ$00$'$00$''$) were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325,694 sources are detected with a signal of at least five times the noise, and the source density is a factor of $\sim 10$ higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S$_{\rm 144 MHz} = 71\,\mu$Jy beam$^{-1}$ and the point-source completeness is 90% at an integrated flux density of 0.45mJy. The resolution of the images is 6$''$ and the positional accuracy is within 0.2$''$. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further $\sim$20 articles that highlight the scientific potential of LoTSS., Comment: 16 figures, 1 table and 22 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 on lofar-surveys.org upon publication of the journal

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$00$'$00$''$) with a median sensitivity of 71$\mu$Jy/beam and a resolution of 6$''$. In this paper we present photometric redshifts (photo-$z$) for 94.4% of optical sources over this region that are detected in the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) 3$\pi$ 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., Comment: 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

Historically, the blazar population has been poorly understood at low frequencies because survey sensitivity and angular resolution limitations have made it difficult to identify megahertz counterparts. We used the LOFAR Two-Metre Sky Survey (LoTSS) first data release value-added catalogue (LDR1) to study blazars in the low-frequency regime with unprecedented sensitivity and resolution. We identified radio counterparts to all $98$ known sources from the Third \textit{Fermi}-LAT Point Source Catalogue (3FGL) or Roma-BZCAT Multi-frequency Catalogue of Blazars ($5^{\mathrm{th}}$ edition) that fall within the LDR1 footprint. Only the 3FGL unidentified $\gamma$-ray sources (UGS) could not be firmly associated with an LDR1 source; this was due to source confusion. We examined the redshift and radio luminosity distributions of our sample, finding flat-spectrum radio quasars (FSRQs) to be more distant and more luminous than BL Lacertae objects (BL Lacs) on average. Blazars are known to have flat spectra in the gigahertz regime but we found this to extend down to $144$ MHz, where the radio spectral index, $\alpha$, of our sample is $-0.17 \pm 0.14$. For BL Lacs, $\alpha = -0.13 \pm 0.16$ and for FSRQs, $\alpha = -0.15 \pm 0.17$. We also investigated the radio-to-$\gamma$-ray connection for the $30$ $\gamma$-ray-detected sources in our sample. We find Pearson's correlation coefficient is $0.45$ ($p = 0.069$). This tentative correlation and the flatness of the spectral index suggest that the beamed core emission contributes to the low-frequency flux density. We compare our sample distribution with that of the full LDR1 on colour-colour diagrams, and we use this information to identify possible radio counterparts to two of the four UGS within the LDR1 field. We will refine our results as LoTSS continues., Comment: 7 figures, 6 tables and 11 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 on lofar-surveys.org upon publication of the journal

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., Comment: 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

Determining the star-forming properties of radio-quiet quasars is important for understanding the co-evolution of star formation and black hole accretion. Here, we present the detection of the gravitationally-lensed radio-quiet quasars SDSS J1055+4628, SDSS J1313+5151 and SBS 1520+530 at 144 MHz that fall in the HETDEX Spring Field targeted in the LOFAR Two-metre Sky Survey (LoTSS) first full data release. We compare their radio and far-infrared luminosities relative to the radio-infrared correlation and find that their radio luminosities can be explained by star formation. The implied star formation rates derived from their radio and infrared luminosities are between 20 and 300 $\rm{M_{\odot}~yr^{-1}}$. These detections represent the first study of gravitationally lensed sources with LOFAR, opening a new frequency window for investigating the star-forming properties of high-redshift quasars at radio wavelengths. We consider the implications for future data releases and estimate that many of the objects in our parent sample will be detected during LoTSS, significantly increasing the fraction of gravitationally lensed radio-quiet quasars with radio detections., Comment: 7 figures, 2 tables and 10 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 on lofar-surveys.org upon publication of the journal

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., Comment: 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

Context: New generation low-frequency telescopes are exploring a new parameter space in terms of depth and resolution. The data taken with these interferometers, for example with the LOw Frequency ARray (LOFAR), are often calibrated in a low signal-to-noise ratio regime and the removal of critical systematic effects is challenging. The process requires an understanding of their origin and properties. Aim: In this paper we describe the major systematic effects inherent to next generation low-frequency telescopes, such as LOFAR. With this knowledge, we introduce a data processing pipeline that is able to isolate and correct these systematic effects. The pipeline will be used to calibrate calibrator observations as the first step of a full data reduction process. Methods: We processed two LOFAR observations of the calibrator 3C196: the first using the Low Band Antenna (LBA) system at 42-66 MHz and the second using the High Band Antenna (HBA) system at 115-189 MHz. Results: We were able to isolate and correct for the effects of clock drift, polarisation misalignment, ionospheric delay, Faraday rotation, ionospheric scintillation, beam shape, and bandpass. The designed calibration strategy produced the deepest image to date at 54 MHz. The image has been used to confirm that the spectral energy distribution of the average radio source population tends to flatten at low frequencies. Conclusions: We prove that LOFAR systematic effects can be described by a relatively small number of parameters. Furthermore, the identification of these parameters is fundamental to reducing the degrees of freedom when the calibration is carried out on fields that are not dominated by a strong calibrator., Comment: 20 pages, 15 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

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

We present observations of the XMM Large-Scale Structure (XMM-LSS) field observed with the LOw Frequency ARray (LOFAR) at 120-168 MHz. Centred at a J2000 declination of $-4.5^{\circ}$, this is a challenging field to observe with LOFAR because of its low elevation with respect to the array. The low elevation of this field reduces the effective collecting area of the telescope, thereby reducing sensitivity. This low elevation also causes the primary beam to be elongated in the north-south direction, which can introduce side lobes in the synthesised beam in this direction. However the XMM-LSS field is a key field to study because of the wealth of ancillary information, encompassing most of the electromagnetic spectrum. The field was observed for a total of 12 hours from three four-hour LOFAR tracks using the Dutch array. The final image presented encompasses $\sim 27$ deg$^2$, which is the region of the observations with a $>$50\% primary beam response. Once combined, the observations reach a central rms of 280 $\mu$Jy beam$^{-1}$ at 144 MHz and have an angular resolution of $7.5 \times \ 8.5$". We present our catalogue of detected sources and investigate how our observations compare to previous radio observations. This includes investigating the flux scale calibration of these observations compared to previous measurements, the implied spectral indices of the sources, the observed source counts and corrections to obtain the true source counts, and finally the clustering of the observed radio sources., Comment: 15 figures, 8 tables and 24 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 on lofar-surveys.org upon publication of the journal

This paper presents a study of the local radio source population, by cross-comparing the data from the first data release (DR1) of the LOFAR Two-Metre Sky Survey (LoTSS) with the Sloan Digital Sky Survey (SDSS) DR7 main galaxy spectroscopic sample. The LoTSS DR1 provides deep data (median rms noise of 71 $\mathrm{\mu}$Jy at 150 MHz) over 424 square degrees of sky, which is sufficient to detect 10615 (32 per cent) of the SDSS galaxies over this sky area. An improved method to separate active galactic nuclei (AGN) accurately from sources with radio emission powered by star formation (SF) is developed and applied, leading to a sample of 2121 local ($z < 0.3$) radio AGN. The local 150 MHz luminosity function is derived for radio AGN and SF galaxies separately, and the good agreement with previous studies at 1.4 GHz suggests that the separation method presented is robust. The prevalence of radio AGN activity is confirmed to show a strong dependence on both stellar and black hole masses, remarkably reaching a fraction of 100 per cent of the most massive galaxies ($> 10^{11} \mathrm{M_{\odot}}$) displaying radio-AGN activity with $L_{\rm 150 MHz} \geq 10^{21}$W Hz$^{-1}$; thus, the most massive galaxies are always switched on at some level. The results allow the full Eddington-scaled accretion rate distribution (a proxy for the duty cycle) to be probed for massive galaxies. More than 50 per cent of the energy is released during the $\le 2$ per cent of the time spent at the highest accretion rates, $L_{\mathrm{mech}}/L_{\mathrm{Edd}} > 10^{-2.5}$. Stellar mass is shown to be a more important driver of radio-AGN activity than black hole mass, suggesting a possible connection between the fuelling gas and the surrounding halo. This result is in line with models in which these radio AGN are essential for maintaining the quenched state of galaxies at the centres of hot gas haloes., Comment: 14 pages, 8 figures, 3 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

Asymmetries in HI in galaxies are often caused by the interaction with close companions, making isolated galaxies an ideal framework to study secular evolution. The AMIGA project has demonstrated that isolated galaxies show the lowest level of asymmetry in their HI integrated profiles, yet some present significant asymmetries. CIG 96 (NGC 864) is a representative case reaching a 16% level. Our aim is to investigate the HI asymmetries of this spiral galaxy and what processes have triggered the star-forming regions observed in the XUV pseudoring. We performed deep optical observations at CAHA 1.23m, 2.2m and VST telescopes. We reach surface brightness (SB) limits of mu_2.2m = 27.5 mag arcsec-2 (Cous R) and mu_VST = 28.7mag arcsec-2 (r) that show the XUV pseudoring of the galaxy in detail. Additionally, a wavelet filtering of the HI data cube from our deep observations with E/VLA telescope allowed us to reach a column density of N_HI = 8.9x10^18 cm -2 (5sigma) (28"x28" beam), lower than in any isolated galaxy. We confirm that the HI extends farther than 4xr_25 in all directions. Furthermore, we detect for the first time two gaseous structures (10^6 Msol) in the outskirts. The g-r colour index image from 1.23m shows extremely blue colours in certain regions of the pseudoring where N_HI>8.5x10^20 cm-2 , whereas the rest show red colours. Galactic cirrus contaminate the field, setting an unavoidable detection limit at 28.5mag arcsec-2 (r). We detect no stellar link within 1degx1deg or gaseous link within 40'x40' between CIG 96 and any companion. The isolation criteria rule out interactions with other similar-sized galaxies for at least 2.7Gyr. Using existing stellar evolution models, the age of the pseudoring is estimated at 1Gyr or older. Undetected previously accreted companions and cold gas accretion remain as the main hypothesis to explain the optical pseudoring and HI features of CIG 96., Comment: 23 pages, 18 figures, 4 tables

Mergers of galaxies are an important mode for galaxy evolution because they serve as an efficient trigger of powerful starbursts. However, observational studies of the molecular gas properties during their early stages are scarce. We present interferometric CO(2-1) maps of two luminous infrared galaxies (LIRGs), NGC 3110 and NGC 232, obtained with the Submillimeter Array (SMA) with ~ 1 kpc resolution. While NGC 3110 is a spiral galaxy interacting with a minor (14:1 stellar mass) companion, NGC 232 is interacting with a similarly sized object. We find that such interactions have likely induced in these galaxies enhancements in the molecular gas content and central concentrations, partly at the expense of atomic gas. The obtained molecular gas surface densities in their circumnuclear regions are $\Sigma_{\rm mol}~\gtrsim10^{2.5}$ M$_\odot$ pc$^{-2}$, higher than in non-interacting objects by an order of magnitude. Gas depletion times of ~ 0.5 - 1 Gyr are found for the different regions, lying in between non-interacting disk galaxies and the starburst sequence. In the case of NGC 3110, the spiral arms show on average 0.5 dex shorter depletion times than in the circumnuclear regions if we assume a similar H$_2$-CO conversion factor. We show that even in the early stages of the interaction with a minor companion, a starburst is formed along the circumnuclear region and spiral arms, where a large population of SSCs is found (~350), and at the same time a large central gas concentration is building up which might be the fuel for an active galactic nucleus. The main morphological properties of the NGC 3110 system are reproduced by our numerical simulations and allow us to estimate that the current epoch of the interaction is at ~ 150 Myrs after closest approach., Comment: 30 pages. Accepted for publication in ApJ

The radio and far-infrared luminosities of star-forming galaxies are tightly correlated over several orders of magnitude; this is known as the far-infrared radio correlation (FIRC). Previous studies have shown that a host of factors conspire to maintain a tight and linear FIRC, despite many models predicting deviation. This discrepancy between expectations and observations is concerning since a linear FIRC underpins the use of radio luminosity as a star-formation rate indicator. Using LOFAR 150MHz, FIRST 1.4 GHz, and Herschel infrared luminosities derived from the new LOFAR/H-ATLAS catalogue, we investigate possible variation in the monochromatic (250$\mathrm{\mu m}$) FIRC at low and high radio frequencies. We use statistical techniques to probe the FIRC for an optically-selected sample of 4,082 emission-line classified star-forming galaxies as a function of redshift, effective dust temperature, stellar mass, specific star formation rate, and mid-infrared colour (an empirical proxy for specific star formation rate). Although the average FIRC at high radio frequency is consistent with expectations based on a standard power-law radio spectrum, the average correlation at 150MHz is not. We see evidence for redshift evolution of the FIRC at 150MHz, and find that the FIRC varies with stellar mass, dust temperature and specific star formation rate, whether the latter is probed using MAGPHYS fitting, or using mid-infrared colour as a proxy. We can explain the variation, to within 1$\sigma$, seen in the FIRC over mid-infrared colour by a combination of dust temperature, redshift, and stellar mass using a Bayesian partial correlation technique., Comment: Accepted for publication in MNRAS. 23 pages, 24 figures, 2 appendices

Massive Ultracompact Galaxies (MUGs) are common at z=2-3, but very rare in the nearby Universe. Simulations predict that the few surviving MUGs should reside in galaxy clusters, whose large relative velocities prevent them from merging, thus maintaining their original properties (namely stellar populations, masses, sizes and dynamical state). We take advantage of the high-completeness, large-area spectroscopic GAMA survey, complementing it with deeper imaging from the KiDS and VIKING surveys. We find a set of 22 bona-fide MUGs, defined as having high stellar mass (>8x10^10 M_Sun) and compact size (R_e<2 Kpc) at 0.02 < z < 0.3. An additional set of 7 lower-mass objects (6x10^10 < M_star/M_Sun < 8x10^10) are also potential candidates according to typical mass uncertainties. The comoving number density of MUGs at low redshift (z < 0.3) is constrained at $(1.0\pm 0.4)x 10^-6 Mpc^-3, consistent with galaxy evolution models. However, we find a mixed distribution of old and young galaxies, with a quarter of the sample representing (old) relics. MUGs have a predominantly early/swollen disk morphology (Sersic index 1 ~ 10^10 M_Sun Kpc^-2). Interestingly, a large fraction feature close companions -- at least in projection -- suggesting that many (but not all) reside in the central regions of groups. Halo masses show these galaxies inhabit average-mass groups. As MUGs are found to be almost equally distributed among environments of different masses, their relative fraction is higher in more massive overdensities, matching the expectations that some of these galaxies fell in these regions at early times. However, there must be another channel leading some of these galaxies to an abnormally low merger history because our sample shows a number of objects that do not inhabit particularly dense environments. (abridged), Comment: 22 pages, 16 figures, 6 tables. Accepted in A&A. Minor revisions in text and figures. Key plots: Environment->Fig. 13, Number densities->Fig. 14

The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical community. A key element of the Astropy project is the core package Astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of inter-operable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy project., Comment: Minor changes to author list and title. Comments and feedback welcome through the paper source repository: https://github.com/astropy/astropy-v2.0-paper For more information about Astropy, see http://www.astropy.org/

We present a study of the low-frequency radio properties of star forming (SF) galaxies and active galactic nuclei (AGN) up to redshift $z=2.5$. The new spectral window probed by the Low Frequency Array (LOFAR) allows us to reconstruct the radio continuum emission from 150 MHz to 1.4 GHz to an unprecedented depth for a radio-selected sample of $1542$ galaxies in $\sim 7~ \rm{deg}^2$ of the LOFAR Bo\"otes field. Using the extensive multi-wavelength dataset available in Bo\"otes and detailed modelling of the FIR to UV spectral energy distribution (SED), we are able to separate the star-formation (N=758) and the AGN (N=784) dominated populations. We study the shape of the radio SEDs and their evolution across cosmic time and find significant differences in the spectral curvature between the SF galaxy and AGN populations. While the radio spectra of SF galaxies exhibit a weak but statistically significant flattening, AGN SEDs show a clear trend to become steeper towards lower frequencies. No evolution of the spectral curvature as a function of redshift is found for SF galaxies or AGN. We investigate the redshift evolution of the infrared-radio correlation (IRC) for SF galaxies and find that the ratio of total infrared to 1.4 GHz radio luminosities decreases with increasing redshift: $ q_{\rm 1.4GHz} = (2.45 \pm 0.04) \times (1+z)^{-0.15 \pm 0.03} $. Similarly, $q_{\rm 150MHz}$ shows a redshift evolution following $ q_{\rm 150GHz} = (1.72 \pm 0.04) \times (1+z)^{-0.22 \pm 0.05}$. Calibration of the 150 MHz radio luminosity as a star formation rate tracer suggests that a single power-law extrapolation from $q_{\rm 1.4GHz}$ is not an accurate approximation at all redshifts., Comment: Accepted for publication in MNRAS, 21 pages, 16 figures

New scientific instruments are starting to generate an unprecedented amount of data. LOFAR, one of the Square Kilometre Array pathfinders, is already producing data on a petabyte scale. The calibration of these data presents a huge challenge for final users: a) extensive storage and computing resources are required; b) the installation and maintenance of the processing software is not trivial; and c) the requirements of (experimental) calibration pipelines are quickly evolving. After encountering some limitations in classical infrastructures, we investigated the viability of cloud infrastructures as a solution. We found that the installation and operation of LOFAR data calibration pipelines is not only possible, but can also be efficient in cloud infrastructures. The main advantages were: (1) ease of software installation and maintenance, and the availability of standard APIs and tools, widely used in the industry; this reduces the requirement for significant manual intervention, which can have a highly negative impact; (2) flexibility to adapt the infrastructure to the needs of the problem, especially as those demands change over time; (3) on-demand consumption of (shared) resources. We found no significant impediments associated with the speed of data transfer, the use of external block storage, or the memory available. However, the availability of scratch storage areas of an appropriate size is critical. Finally, we considered the cost-effectiveness of a commercial cloud like Amazon Web Services. While it is more expensive than the operation of a large, fully-utilised cluster completely dedicated to LOFAR data reduction, its costs are competitive if the number of datasets to be analysed is not high, or if the costs of maintaining the dedicated system become high. Coupled with the advantages discussed above, this suggests that a cloud infrastructure may be favourable for many users., Comment: 18 pages, 6 figures, 3 tables, accepted for publication in Astronomy and Computing

New tools are needed to handle the growth of data in astrophysics delivered by recent and upcoming surveys. We aim to build open-source, light, flexible, and interactive software designed to visualize extensive three-dimensional (3D) tabular data. Entirely written in the Python language, we have developed interactive tools to browse and visualize the positions of galaxies in the universe and their positions with respect to its large-scale structures (LSS). Motivated by a previous study, we created two codes using Mollweide projection and wedge diagram visualizations, where survey galaxies can be overplotted on the LSS of the universe. These are interactive representations where the visualizations can be controlled by widgets. We have released these open-source codes that have been designed to be easily re-used and customized by the scientific community to fulfill their needs. The codes are adaptable to other kinds of 3D tabular data and are robust enough to handle several millions of objects., Comment: 7 pages, 2 figures; accepted for publication in PASP Special Focus Issue: Techniques and Methods for Astrophysical Data Visualization