The LOFAR LBA Sky Survey

Abstract

Context. The LOw Frequency ARray (LOFAR) is the only radio telescope that is presently capable of high-sensitivity, high-resolution (i.e. < 1 mJy beam −1 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. Aims. The LOFAR LBA Sky Survey (LoLSS) aims to cover the entire northern sky with 3170 pointings in the frequency range between 42 − 66 MHz, at a resolution of 15 and at a sensitivity of 1 mJy beam −1 (1σ). In this work, we outline the survey strategy, the observational status, and the calibration techniques. We also briefly describe several of our scientific motivations and present the preliminary public data release. Methods. The preliminary images were produced using a fully automated pipeline aimed at correcting all direction-independent effects in the data. Whilst the direction-dependent effects, such as those from the ionosphere, have not yet been corrected, the images presented in this work are still ten times more sensitive than previous available surveys at these low frequencies. Results. The preliminary data release covers 740 deg 2 around the HETDEX spring field region at an angular resolution of 47 with a median noise level of 5 mJy beam −1. The images and the catalogue of 25,247 sources have been publicly released. We demonstrate that the system is capable of reaching a root mean square (rms) noise of 1 mJy beam −1 and an angular resolution of 15 once directiondependent effects are accounted for. Conclusions. LoLSS will provide the ultra-low-frequency information for hundreds of thousands of radio sources, providing critical spectral information and producing a unique data set 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, as well as those produced by active galactic nuclei (AGN).

Accretion mode versus radio morphology in the LOFAR Deep Fields

“…Given the lack of radiative signatures at other wavelengths and their low radio fluxes, meaning that before LOFAR the FRII-Low were only identified in small numbers, their contribution to cosmic evolution might have been underestimated. The importance of their role in galaxy and cluster evolution will be greatly dependent on the duration of their life cycles, which we will be able to constrain with lower frequency, LOFAR LBA observations in the near future (de Gasperin et al 2021 ;Williams et al 2021 ).…”

The ultra-steep diffuse radio emission observed in the cool-core cluster RX J1720.1+2638 with LOFAR at 54 MHz

“…The flux density scale was set according to Scaife & Heald (2012). The flux calibration uncertainty is estimated to be 10 per cent (de Gasperin et al 2021). We imaged the data with WSClean (Offringa et al 2014;Offringa & Smirnov 2017) using a Briggs weighting scheme with robust = −0.5, applying an inner uv-cut at 30λ and using a multiscale deconvolution.…”

Radio spectral properties of star-forming galaxies in the MIGHTEE-COSMOS field and their impact on the far-infrared-radio correlation

“…To improve quality and sample size in studying the radio spectral properties at both low and high frequency, observations with similar spatial resolutions and high sensitivity at multiple frequencies are essential. The recently released high-sensitivity lowfrequency (< 150 MHz) data from the Low Frequency Array (LO-FAR) large surveys (e.g., de Gasperin et al 2021;Tasse et al 2021;Sabater et al 2021) and the undergoing joint project, SuperMIGH-TEE, which combines the MeerKAT and uGMRT telescopes to observe the MIGHTEE survey regions at 0.5-2.7 GHz with the same angular resolution (∼ 5 ′′ ) and similar sensitivity, will dramatically advance the studies of the radio spectrum.…”