MeerKAT observations of Abell 1775 and Abell 1795: the discovery of a hadronic radio halo?
Year: 2026
Type: article
Abstract: ABSTRACT Giant radio haloes are diffuse synchrotron sources typically found in merging galaxy clusters, while smaller mini-haloes occur in cool-core clusters. Both trace cosmic-ray electrons in the intracluster medium, though recent observations suggest their distinction is not always clear. We present new 903–1655 MHz MeerKAT observations of Abell 1775 and Abell 1795, both hosting cool cores and cold fronts. Combined with reprocessed 120–168 MHz LOFAR Two-metre Sky Survey data, we perform imaging and spectral analyses of their radio emission. In both clusters, we detect radio haloes with distinct inner and outer components. In Abell 1775, the halo appears diffuse at 1.3 GHz, while LOFAR images reveal steep-spectrum filaments. In Abell 1795, the inner component corresponds to a previously reported mini-halo candidate, but the full structure extends to $\sim$1 Mpc with a spectral index of $\alpha =-1.08\pm 0.06$. The presence of such a large, flat-spectrum halo in a dynamically relaxed cluster makes Abell 1795 an outlier relative to typical merging systems. This suggests that some relaxed clusters may still retain sufficient turbulence to sustain particle re-acceleration, or that hadronic interactions producing secondary electrons play a significant role. Together with other recent discoveries in cool-core systems, our results indicate that some large radio haloes may have been overlooked in past studies due to limited dynamic range near bright central AGN. Finally, we detect steep-spectrum emission south of Abell 1795’s central AGN, tracing a 45 kpc X-ray and optical filament that terminates in an X-ray cavity, likely linked to a past AGN outburst.
Institutions: Leiden University, Leiden Observatory, University of Toronto, Istituto di Radioastronomia di Bologna, National Institute for Astrophysics, Ruhr University Bochum, Durham University, University of Bologna, Universität Hamburg, Netherlands Institute for Radio Astronomy, Rhodes University, South African Radio Astronomy Observatory, Max Planck Institute for Extraterrestrial Physics
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
Funders: California Department of Fish and Game, Ukrainian Research Institute, Harvard University, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, University of Toronto, Johnson Space Center, Institut sur la Nutrition et les Aliments Fonctionnels, Science and Technology Facilities Council, H2020 European Research Council
OpenAlex ID: W7126043326