LoTSS of dual AGN: Enhanced detectability and prospects for a systematic search
Year: 2026
Type: article
Abstract: Dual active galactic nuclei (DAGN) -- systems of two simultaneously accreting supermassive black holes at kiloparsec-scale separations -- are critical tracers of galaxy mergers and the progenitors of gravitational-wave sources targeted by pulsar timing arrays and the upcoming Laser Interferometer Space Antenna. Despite their importance, their radio properties remain largely unconstrained, particularly at high redshift, due to the limited combination of sensitivity and sky coverage of existing high-angular-resolution surveys. In this pilot project, we primarily aim to demonstrate the detectability of high-redshift DAGN at 144 MHz performing subarcsecond resolution imaging of the LOFAR Two-metre Sky Survey (LoTSS) data, and characterize the low-frequency radio properties of individual systems. We crossmatched a sample of 92 spectroscopically confirmed DAGN at z > 0.3 and projected separation r_p < 30 kpc with the LoTSS catalogs of data release (DR) 2 (resolution ∼6 and reprocessed the international LOFAR telescope (ILT) LoTSS data for three sources spanning 0.59 < z < 2.39, achieving ∼0.3 resolution at 144 MHz. We performed a multifrequency analysis and brightness temperature diagnostics to characterize the AGN nature and radio properties of each system. We successfully produced high-quality ILT images for the three DAGN in the pilot sample. In one source at z = 1.49, we detected both AGN components at $>5σ$, making it one of the highest-z and faintest DAGN detected at radio frequencies. Brightness temperature measurements confirm that ILT 144 MHz observations can efficiently distinguish AGN-powered emission from star formation even in sub-milliJansky sources. In the other two sources, we detected only one AGN. In one of them, the new ILT imaging constrains the low-frequency radio spectrum of the compact steep spectrum source, indicating that its complex morphology is shaped by jet-interstellar medium interaction rather than by the companion galaxy. In addition, for the full 92 DAGN sample, we found a detection rate of ∼24% in both LoTSS DR2 and DR3, significantly higher than that of single AGN matched in selection (∼9--10%), suggesting an enhanced detectability of DAGN in LoTSS. Low-frequency, subarcsecond-resolution radio observations constitute a highly efficient and dust-unbiased pathway to detect, confirm, and characterize DAGN across cosmic time. The pilot sample presented here establishes the foundation for a systematic DAGN search in the upcoming all-sky ∼0.3 resolution international LoTSS (ILoTSS) and provides an early benchmark for the future Square Kilometre Array (SKA) observations.
Source: Astronomy and Astrophysics
Authors: Q. D'Amato, F. Mannucci, E. De Rubeis, I. Prandoni, A. De Rosa, M Scialpi, M. Kunert-Bajraszewska, A. Janiuk, A. Krauze, L. Battistini, E. Bertola, C. Bracci, A. Chakraborty, M. Ceci, C. Cicone, G. Cresci, A. Marconi, C. Marconcini, E. Nardini, M. Parvatikar, A. Peca, K. Rubinur, P. Severgnini, C. Spingola, L. Ulivi, G. Venturi, C. Vignali, M. V. Zanchettin
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Radio Astronomy Observatory, University of Hertfordshire, Science Foundation Ireland, Deutsche Forschungsgemeinschaft, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Max-Planck-Gesellschaft, Centre National de la Recherche Scientifique, Istituto Nazionale di Astrofisica, Université d'Orléans, Agencia Nacional de Investigación y Desarrollo, Gauss Centre for Supercomputing, Observatoire de Paris, Université de Recherche Paris Sciences et Lettres, Science and Technology Facilities Council
OpenAlex ID: W7214040301