The LOFAR Two-metre Sky Survey : VII. Third data release
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EDP Sciences
Abstract
We present the third data release of the LOFAR Two-metre Sky Survey (LoTSS-DR3). The survey images cover 88% of the northern sky and were created from 12 950 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.
Description
DATA AVAILABILITY STATEMENT: The LoTSS-DR3 data products are publicly available and can be accessed via the LOFAR Surveys webpage (https://lofar-surveys.org/dr3_release.html), theSURF data repository (https://doi.org/10.25606/SURF.lotss-dr3), or the ASTRON Virtual Observatory (https://vo.astron.nl). The source catalogue is also available at the CDS via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/707/A198. The data collection in this release has the Digital Object Identifier (DOI) 10.25606/SURF.LoTSS-DR3, and each individual data product is assigned a unique ePIC persistent identifier (ePIC-PID). Thedata products include:
– 2551 individual field full depth Stokes I 600 and 2000 resolution continuum images (900 and 2000 for declinations below10◦) each covering 8◦ × 8◦and with a median sensitivity (excluding fields within 10◦ of the galactic plane) of112 µJy/beam in the higher resolution maps.
– 2551 sets of individual field Stokes V 600 (900 for declinations below 10◦) resolution continuum images where an image is provided for each epoch (up to 6 epochs per field).
– 2551 individual field Stokes Q and U 2000 and 40 resolution cubes (typically 462 channels of width 97.6 kHz).
– 2551 sets of individual field uv data and direction-dependent calibration solutions (at a time resolution of 8 s and frequency resolution of 97.6 kHz).
– 1580 mosaicked Stokes I 600 and 2000 resolution continuum images centred on HEALPix pixels with NSIDE=16 (900 and 2000 for declinations below 10◦).
– A merged PyBDSF catalogue of 13 667 877 sources and the corresponding 16 943 656 Gaussian components derived from all Stokes I 600 resolution mosaics. The columns are described in Table A.1 and are a subset of those provided by default by PyBDSF, including position, integrated flux density, peak brightness, size, and estimated statistical errors on all parameters (but not including flux density scale or astrometric alignment errors, which should be added appropriately during analysis). We add additional columns with the identity of the mosaic in which a source was detected and the angular resolution of the mosaic image.
The final DDF-pipeline data products for the 2551 fields processed are 590 TB in size, of which 8% is Stokes I images, 24% is Stokes Q, U, and V images and 67% is uv data and associated calibration solutions. The 18.6 PB of uncalibrated LoTSS data that were used for LoTSS-DR3 are also publicly available and can be retrieved from the LOFAR LTA.
Keywords
Instrumentation: interferometers, Catalogs, Surveys, Radio continuum: general, Sky survey, Space sustainability, LOFAR Two-metre Sky Survey (LoTSS-DR3)
Sustainable Development Goals
None
Citation
Shimwell, T. W., Hardcastle, M. J., Tasse, C. et al. 2026, ‘The LOFAR two-metre sky survey: VII. third data release’, Astronomy & Astrophysics, vol. 707, art. A198: 1–22, doi: 10.1051/0004-6361/202557749.