Current Fellow

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A Systematic Search for Merging Black Holes in the Early Universe
Xin Liu
Fellow 2017-18

Dual Active Galactic Nuclei (AGNs) are active supermassive black hole pairs co-rotating in merging galaxies. Despite decades of searching, and strong reasons to believe they exist, unambiguously confirmed dual AGNs are surprisingly scarce, which contradicts theoretical prediction. To date no confirmed case of dual AGNs is known at cosmic redshift z>2.

During her Center appointment, Professor Liu will employ a new technique to identify z>2 dual AGNs to fill this gap. The technique makes use of variability of the AGN light curves, and searches for the centroid shift due to the non-synchronous variation of two closely separated AGNs. This technique will be applied to data from time-domain surveys such as the Dark Energy Survey. Higher resolution imaging and spectroscopic follow-up observations will be conducted to confirm the dual AGN candidates and to assess the efficiency and feasibility of the technique.

Preliminary results suggest that the technique is capable of identifying dual AGNs at redshifts up to z>2 (i.e., probing the cosmic “high noon” when mergers should be most common), and can achieve an order-of-magnitude increase over the telescope angular resolution limit. If confirmed, this result would imply that hundreds and thousands of dual AGNs could be identified through most of the early cosmic history with ongoing and future surveys, thereby opening a new window onto the study of galaxy evolution, cosmology, and gravitational wave astronomy.