Title: Merging black holes in merging galaxies: linking astrophysics and fundamental physics

Abstract: Massive black holes (MBHs), up to billions times more massive than the sun, lurk at the hearts of essentially all galaxies. One of the most efficient ways to grow these BHs is through mergers of galaxies, during which tidal interactions funnel large amounts of gas to the galaxies’ centers, to feed the MBHs. Eventually, the dual MBHs may collide, releasing gravitational waves and potentially forming recoiling MBHs that may escape the merger remnant. While several future GW facilities are designed to chase these enticing high-amplitude and low-frequency signals through cosmic history, most other parts of this astrophysical story are yet to be corroborated by observations, even in the nearby universe. I will present recent and on-going efforts to identify and survey the population of merging MBHs in merging galaxies, pursued with observations across the electromagnetic spectrum with particular focus on ALMA. I will focus on high-resolution observations using both large ground-based telescopes with “adaptive optics'' and space-borne telescopes, which have enabled the identification of dual MBHs, and their links to powerful/enhanced accretion. I will also mention current and future observational efforts with ALMA and the JVLA to survey hard X-ray selected AGN and molecular gas within the BASS Survey of hard X-ray selected AGN.