The Planck clusters in the LOFAR sky

Abstract

Context. Relativistic electrons and magnetic fields permeate the intra-cluster medium (ICM) and manifest themselves as diffuse sources of synchrotron emission observable at radio wavelengths, namely radio halos and radio relics. Although there is broad consensus that the formation of these sources is connected to turbulence and shocks in the ICM, the details of the required particle acceleration, the strength and morphology of the magnetic field in the cluster volume, and the influence of other sources of high-energy particles are poorly known. Aims. Sufficiently large samples of radio halos and relics, which would allow us to examine the variation among the source population and pinpoint their commonalities and differences, are still missing. At present, due to the physical properties of the sources and the capabilities of existing facilities, large numbers of these sources are easiest to detect at low radio frequencies, where they shine brightly. Methods. We examined the low-frequency radio emission from all 309 clusters in the second catalog of Planck Sunyaev Zel’dovich detected sources that lie within the 5634 deg2 covered by the Second Data Release of the LOFAR Two-meter Sky Survey (LoTSS-DR2). We produced LOFAR images at different resolutions, with and without discrete sources subtracted, and created overlays with optical and X-ray images before classifying the diffuse sources in the ICM, guided by a decision tree. Results. Overall, we found 83 clusters that host a radio halo and 26 that host one or more radio relics (including candidates). About half of them are new discoveries. The detection rate of clusters that host a radio halo and one or more relics in our sample is 30 ± 11% and 10 ± 6%, respectively. Extrapolating these numbers, we anticipate that once LoTSS covers the entire northern sky it will provide the detection of 251 ± 92 clusters that host a halo and 83 ± 50 clusters that host at least one relic from Planck clusters alone. All images and results produced in this work are publicly available via the project website.

Diffuse radio emission from non-Planckgalaxy clusters in the LoTSS-DR2 fields

“…To improve the image fidelity towards the target direction, we follow the 'extraction' and self-calibration procedure that post-processes the archived ddf − pipeline products and is described in van Weeren et al (2021) and Botteon et al (2022). To maximise the signal-to-noise ratio (S/N) of the detected sources, we include all the data from LoTSS-DR2 pointings that are centred within 2.2 • from the target cluster.…”

“…Finally, multiple self-calibration loops including phase and phase-amplitude are performed. For details, we refer to van Weeren et al ( 2021) and Botteon et al (2022).…”

“…In order to search for cluster-scale emission, we follow the imaging procedure for the PSZ2 clusters in Botteon et al (2022) to obtain images of our targets at several different angular resolutions using WSClean 4 (version 2.10.0). To alter the resolution, we image with a Briggs' weighting robust parameter of −0.5 without and with a tapering of outer baselines (i.e.…”

“…Using the LoTSS first data release (LoTSS-DR1; Shimwell et al 2019), van Weeren et al (2021) studied the diffuse emission in 41 galaxy clusters located in the 424 deg 2 of the HETDEX Spring region. More recently, Botteon et al (2022) analysed all the galaxy clusters reported in the second catalogue of SZ-detected sources (PSZ2; Ade et al 2016) within the 5634 deg 2 area covered by the LoTSS -Second Data Release (LoTSS-DR2; Shimwell et al 2022). Botteon et al (2022) found that among the 309 galaxy clusters selected from the PSZ2 catalogue with 0.016 < z < 0.9 and 1.1×10 14 M ⊙ < M 500 < 11.7×10 14 M ⊙ , 83 clusters host a radio halo and 26 clusters host one or more radio relics (including candidates).…”

“…In this paper, we present our search for radio diffuse emission in galaxy clusters that are missed by these studies (i.e. van Botteon et al 2022) in non-PSZ2 clusters in the LoTSS-DR2 area. As the SZ signal is proportional to the mass of the ICM gas (e.g.…”