Seminars at FGG
Identifying Dual AGN Candidates at Sub-Arcsecond Scales
Speaker: Maria Vittoria Zanchettin (INAF - Osservatorio di Arcetri (Firenze, Italy))
Date and time: 2025-02-26 11:30
Cosmological models predict the existence of dual supermassive black holes (SMBHs) in-spiraling at galaxy centers. These systems undergo orbital decay via dynamical friction, form a gravitationally bound binary, and eventually merge, generating intense gravitational waves (GWs). Dual active galactic nuclei (AGN) at kiloparsec separations consist of two active nuclei powered by accretion onto separate SMBHs. These systems are fundamental for testing SMBH formation and evolution models. Moreover, SMBH mergers emit GW signals detectable by the future Laser Interferometer Space Antenna (LISA) mission and Pulsar Timing Arrays. Dual AGN within 10 kpc are predicted to be common at z>0.5, yet few are known. I will present how the recently developed Gaia Multi-Peak (GMP) method (Mannucci et al. 2022) enabled the selection of numerous dual AGN candidates at sub-arcsecond separations. A key next step is determining whether GMP-selected systems are multiple AGNs, gravitationally lensed systems, or an AGN plus a foreground star. Ground-based spectroscopy, such as with TNG, can reveal stellar features at zero velocity, indicating a nearby star. However, spectral differences between dual and lensed systems are typically too subtle to detect in the total spectrum. Thus, final classification relies on spatially resolved spectroscopy from space or adaptive-optics (AO)-assisted spectroscopy from the ground. Finally, I will present initial results on the physical properties of dual systems, including masses, luminosities, separation distribution, and redshift evolution. These findings highlight the need for larger dual AGN samples to refine statistical outcomes, validate galaxy evolution models, and predict event rates for PTA-detectable signals in the near future.