Year: 2025
Type: article
Abstract: Aims. The orientation-based unification scheme of radio-loud active galactic nuclei (AGNs) asserts that radio galaxies and quasars are essentially the same type of object, but viewed from different angles. To test this unification model, we compared the environments of radio galaxies and quasars, which would reveal similar properties when an accurate model is utilized. Methods. Using the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2), we constructed a sample of 26 577 radio galaxies and 2028 quasars at 0.08 < z < 0.4. For radio galaxies with optical spectra, we further classified them as 3631 low-excitation radio galaxies (LERGs) and 1143 high-excitation radio galaxies (HERGs). We crossmatched these samples with two galaxy cluster catalogs from the Sloan Digital Sky Survey (SDSS). Results. We find that 17.1 ± 0.2% of the radio galaxies and 4.1 ± 0.4% of the quasars are associated with galaxy clusters. Luminous quasars are very rare in clusters, while 18.7 ± 0.7% LERGs and 15.2 ± 1.1% HERGs reside in clusters. We also note that in radio galaxies, both HERGs and LERGs tend to reside in the centers of clusters, while quasars do not show a strong preference for their positions in clusters. Conclusions. This study shows that local quasars and radio galaxies exist in different environments, challenging the orientation-based unification model. This means that factors other than orientation may play an important role in distinguishing radio galaxies from quasars. The future WEAVE-LOFAR survey will offer high-quality spectroscopic data for a large number of radio sources and allow for a more comprehensive exploration of the environments of radio galaxies and quasars.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Smithsonian Institution, Alfred P. Sloan Foundation, Yale University, Carnegie Institution of Washington, Ohio State University, California Institute of Technology, Harvard University, Johns Hopkins University, New Mexico State University, Space Telescope Science Institute, European Space Agency, Flatiron Health, École Polytechnique Fédérale de Lausanne, Universiteit Leiden, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, University of Toronto, China Scholarship Council, Centre National de la Recherche Scientifique, Universidad Nacional Autónoma de México, Yunnan University, Nanjing University, China National Textile and Apparel Council, Leibniz-Institut für Astrophysik Potsdam, Max-Planck-Institut für Astronomie, University of Illinois at Urbana-Champaign, Smithsonian Astrophysical Observatory, Leibniz-Gemeinschaft, National Astronomical Observatories, Chinese Academy of Sciences
OpenAlex ID: W7125405771
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