Lukas Böhme

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 h of data (18.6 PB) accumulated over 10.5 years. Producing the images took 20 million core hours of processing 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″ (9″ below declination 10°) 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″ 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 μJy beam ⁻¹ , improving to 68 μJy beam ⁻¹ at high observing elevations, but degrading to 183 μJy beam ⁻¹ at the celestial equator due to station area projection effects. 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.

Context. The second data release of the LOFAR Two-Metre Sky Survey (LoTSS-DR2) extends the first data release in terms of sky coverage and source density. It provides the largest radio source catalogue to date, including 4.4 million sources and covering 5635 square degrees of the sky. Therefore, it provides an excellent opportunity for studies of the large-scale structure of the Universe. Aims. We investigated the statistical distribution of source counts in cells and we tested a computationally cheap method based on the counts in cells to estimate the two-point correlation function. Methods. We studied and compared three stochastic models for the counts in cells; these resulted in a Poisson distribution, a compound Poisson distribution, and a negative binomial distribution. By analysing the variance of counts in cells for various cell sizes, we fitted the reduced normalised variance to a single power-law model representing the angular two-point correlation function. Results. Our analysis confirms that radio sources are not Poisson distributed, which is most likely due to multiple physical components of radio sources. Employing instead a Cox process, we show that there is strong evidence in favour of the negative binomial distribution above a flux-density threshold of 2 mJy. Additionally, the mean number of radio components derived from the negative binomial distribution is in good agreement with corresponding estimates based on the value-added catalogue of LoTSS-DR2. The scaling of the counts-in-cells normalised variance with cell size is in good agreement with a power-law model for the angular two-point correlation. At a flux-density threshold of 2 mJy and a signal-to-noise ratio of 7.5 for individual radio sources, we find that for a range of angular scales large enough to not be affected by the multi-component nature of radio sources, the value of the exponent of the power law ranges from −0.8 to −1.05. This closely aligns with findings from previous optical, infrared, and radio surveys of the large-scale structure. Conclusions. The multi-component nature of LoTSS radio sources is essential in order to understand the observed counts-in-cells statistics. The scaling of the counts-in-cells statistics with cell size provides a computationally efficient method for estimating the two-point correlation properties, offering a valuable tool for future large-scale structure studies.

Covering |$\sim 5600\, \deg ^2$| to rms sensitivities of ∼70 −100 μJy beam⁻¹, the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS-DR2) provides the largest low-frequency (∼150 MHz) radio catalogue to date, making it an excellent tool for large-area radio cosmology studies. In this work, we use LoTSS-DR2 sources to investigate the angular two-point correlation function of galaxies within the survey. We discuss systematics in the data and an improved methodology for generating random catalogues, compared to that used for LoTSS-DR1, before presenting the angular clustering for ∼900 000 sources ≥1.5 mJy and a peak signal-to-noise ≥7.5 across ∼80 % of the observed area. Using the clustering we infer the bias assuming two evolutionary models. When fitting angular scales of |$0.5 \le \theta <5\, \deg$|⁠, using a linear bias model, we find LoTSS-DR2 sources are biased tracers of the underlying matter, with a bias of |$b_{C}= 2.14^{+0.22}_{-0.20}$| (assuming constant bias) and |$b_{E}(z=0)= 1.79^{+0.15}_{-0.14}$| (for an evolving model, inversely proportional to the growth factor), corresponding to |$b_E= 2.81^{+0.24}_{-0.22}$| at the median redshift of our sample, assuming the LoTSS Deep Fields redshift distribution is representative of our data. This reduces to |$b_{C}= 2.02^{+0.17}_{-0.16}$| and |$b_{E}(z=0)= 1.67^{+0.12}_{-0.12}$| when allowing preferential redshift distributions from the Deep Fields to model our data. Whilst the clustering amplitude is slightly lower than LoTSS-DR1 (≥2 mJy), our study benefits from larger samples and improved redshift estimates.

Aims. The recent preliminary release of the LOFAR LBA Sky Survey (LoLSS) is the first wide-area, ultra-low frequency observation published from the Low Frequency Array (LOFAR). Our aim is to combine this data set with other surveys at higher frequencies to study the spectral properties of a large sample of radio sources. Methods. We present a new cross-matching algorithm that takes into account the sizes of the radio sources. We applied it to the LoLSS-PR, LoTSS-DR1, LoTSS-DR2 (all LOFAR), TGSS-ADR1 (GMRT), WENSS (WSRT), and NVSS (VLA) catalogues. We then studied the number of matched counterparts for LoLSS radio sources and their spectral properties. Results. We found counterparts for 22 607 (89.5%) LoLSS sources. The remaining 2640 sources (10.5%) were identified either as an artefact in the LoLSS survey (3.6%) or flagged due to their closeness to bright sources (6.9%). We found an average spectral index of α = −0.77 ± 0.18 between LoLSS and NVSS. Between LoLSS and LoTSS-DR2, we found α = −0.71 ± 0.31. The average spectral index is independent of the flux density above S₅₄ = 181 mJy. A comparison of the spectral slopes from LoLSS-LoTSS-DR2 with LoTSS-DR2–NVSS indicates that the probed population of radio sources shows evidence of a negative spectral curvature.