Using a Uniform Sample of Sub-Galactic-Scale Binary Active Galactic Nuclei to Understand Changes in Galaxies Over Time Caused by Galaxy Merging

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Part 1One of the fundamental predictions of the cold dark matter cosmology is that galaxies grow through a series of major and minor mergers with other galaxies. By studying galaxy mergers through detailed observations and theoretical models, we can understand galaxy changes over time in general. Significant progress has been made in the past two decades, but the problem is far from solved. The key physical processes of galaxy merging remain poorly understood. In particular, simulations make predictions that until now have been difficult to identify because of observational challenges, hindering direct comparison between observation and simulation. This proposal seeks to advance our understanding of galaxy changes caused by mergers by eliminating the observational obstacles and characterizing the frequency of binary black holes at small physical scales.Part 2This proposal will identify, confirm, and characterize a sample of kiloparsec-scale binary Active Galactic Nuclei (AGNs). For the first time, the binaries will be identified systematically using high-resolution deep radio and optical surveys in a 275 square degree field. This search will increase the current sample of kiloparsec-scale binary AGNs by an order-of-magnitude. Unbiased by dust-obscuration, the sample will cover a range of host galaxy properties and black-hole-accretion modes. By comparing the uniformly selected binary AGNs with matched control samples, the team will investigate a number of outstanding questions in the merger paradigm of galaxy formation and change: Can mergers trigger and synchronize black hole accretion? What is the origin of the two-accretion/feedback modes (radiative-mode vs. jet-mode)? Can AGN feedback significantly affect the star formation activity on a short timescale (~1,000,000 years)? How frequently does a supermassive black hole oscillate around a stellar core because of gravitational wave recoil or a delay in binary formation? As the immediate precursor of massive black hole binaries, studies of kiloparsec-scale galaxy mergers will also have important implications for low-frequency gravitational wave experiments.