2025A&A...696A..59P

Context. Merger events can trigger gas accretion onto supermassive black holes (SMBHs) located at the centre of galaxies and form close pairs of active galactic nuclei (AGNs). The fraction of AGNs in pairs offers critical insights into the dynamics of galaxy interactions, SMBH growth, and their co-evolution with host galaxies. However, the identification of dual AGNs is difficult, as it requires high-quality spatial and spectral data; hence, very few pairs have been found in the distant Universe so far.
Aims. This study is aimed at providing a first observational estimate of the fraction of dual AGNs at 2 < z < 6 by analysing a sample of 16 AGNs observed with the JWST Near-InfraRed Spectrograph (NIRSpec) in integral field mode, as part of the GA-NIFS survey. For two AGNs in our sample, we also incorporated archival VLT/MUSE data to expand the search area.
Methods. We searched for nearby companion galaxies and emission-line sources within the ∼20 × 20 kpc field of view of the NIRSpec data cubes, extending up to ∼50 kpc using the MUSE data cubes. We analysed the spectra of such emitters to determine their physical and kinematic properties.
Results. We report the serendipitous discovery of a triple AGN system and four dual AGNs (two of which had been considered as candidates), with projected separations in the range 3-28 kpc. The results of this study more than double the number of known multiple AGNs at z > 3 at these separations. Their AGN classification is mainly based on standard optical emission line flux ratios, as observed with JWST/NIRSpec, and complemented with additional multi-wavelength diagnostics. The identification of these 3-5 multiple AGNs out of the 16 AGN systems in the GA-NIFS survey (i.e. ∼20-30%) suggests they might be more common than previously thought from other observational campaigns. Moreover, our inferred fraction of dual AGN moderately exceeds predictions from cosmological simulations that mimic our observational criteria (∼10%).
Conclusions. This work highlights the exceptional capabilities of NIRSpec for detecting distant dual AGNs, prompting new investigations to constrain their fraction across cosmic time.