The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging

Abstract

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 $\sim 80$ and $\sim 100$ hours of integration respectively and reaching unprecedented noise levels at these low frequencies of $\lesssim 30$ and $\lesssim 23$ $\mu$Jy/beam in the inner $\sim 3$ deg${}^2$. This approach is also being used to reduce the LoTSS-wide data for the second data release.

This paper is part of the 1st data release of the LoTSS Deep Fields. Electronic data catalogues will be made available on journal publication

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Cited by in corpus (15)

• The LOFAR Two Metre Sky Survey: Deep Fields Data Release 1 -- III. Host-galaxy identifications and value added catalogues
• The LOFAR Two-metre Sky Survey Deep fields: The star formation rate - radio luminosity relation at low frequencies
• Physical insights from the spectrum of the radio halo in MACS J0717.5+3745
• Low-frequency monitoring of flare star binary CR Draconis: Long-term electron-cyclotron maser emission
• The contribution of discrete sources to the sky temperature at 144 MHz
• Understanding the radio relic emission in the galaxy cluster MACS J0717.5+3745: spectral analysis
• Discovery of a Supercluster in the eROSITA Final Equatorial Depth Survey: X-ray Properties, Radio Halo, and Double Relics
• The best of both worlds: Combining LOFAR and Apertif to derive resolved radio spectral index images
• The bright end of the infrared luminosity functions and the abundance of hyperluminous infrared galaxies
• Diffuse Radio Emission from Galaxy Clusters in the LOFAR Two-metre Sky Survey Deep Fields
• Gravitational lensing in LoTSS DR2 -- Extremely faint 144-MHz radio emission from two highly magnified quasars
• LOFAR Deep Fields: Probing a broader population of polarized radio galaxies in ELAIS-N1
• The LOFAR Two-metre Sky Survey Deep Fields -- Data Release 1: IV. Photometric redshifts and stellar masses
• LOFAR properties of SILVERRUSH Ly$\alpha$ emitter candidates in the ELAIS-N1 field
• Low-frequency radio spectra of submillimetre galaxies in the Lockman Hole