Dual and binary supermassive black holes

We review recent results focused on dual and binary active galactic nuclei (AGN) obtained by our collaboration. Our research, conducted at both low and high redshifts, involves statistical analyses of known AGN pairs (less than 100 kpc of separation), identification of new samples of dual AGN at sub-kpc/kpc scale separation at z>0.5, and investigation of binary AGN candidates (sub-pc separation). Studying these systems over a wide range of frequencies and redshifts contributes to understanding supermassive black hole (SMBH) formation and evolution, and galaxy-SMBH co-evolution, with great relevance for gravitational-wave (GW) experiments. Our findings, consistently with simulations, suggest that galaxy interactions and mergers are likely to induce perturbations that enable the gas to be funneled towards the central nuclear regions and to be accreted efficiently, thus increasing the amount of absorption at close pair separations and possibly the AGN luminosity. We introduced innovative selection techniques, such as the Gaia Multi Peak method, to identify kpc-scale dual AGN beyond the low-redshift Universe, and we addressed challenges in detecting obscured dual AGN. As for binary systems, we identified two highly promising candidates exhibiting possible X-ray periodicity and, in one case, a potential double-peaked iron emission line.