Astrometric Jitter as a Detection Diagnostic for Recoiling and Slingshot Supermassive Black Hole Candidates

TL;DR

This paper proposes a new astrometric jitter method to identify off-nuclear active galactic nuclei, enabling detection of recoiling or slingshot supermassive black holes, with initial candidates found in optical survey data and potential for future surveys.

Contribution

It adapts varstrometry for optical surveys to efficiently find off-nuclear AGNs, demonstrating its effectiveness with new candidates and outlining its applicability to upcoming surveys like LSST.

Findings

Identified five new runaway AGN candidates in Pan-STARRS1 data.

Confirmed one candidate as likely a dual AGN through spectroscopy.

Method is adaptable to future high-cadence, deep surveys like LSST.

Abstract

Supermassive black holes (SMBHs) can be ejected from their galactic centers due to gravitational wave recoil or the slingshot mechanism following a galaxy merger. If an ejected SMBH retains its inner accretion disk, it may be visible as an off-nuclear active galactic nucleus (AGN). At present, only a handful of offset AGNs that are recoil or slingshot candidates have been found, and none have been robustly confirmed. Compiling a large sample of runaway SMBHs would enable us to constrain the mass and spin evolution of binary SMBHs and study feedback effects of displaced AGNs. We adapt the method of varstrometry -- which was developed for Gaia observations to identify off-center, dual, and lensed AGNs -- in order to quickly identify off-nuclear AGNs in optical survey data by looking for an excess of blue versus red astrometric jitter. We apply this to the Pan-STARRS1 3$\pi$ Survey and report on five new runaway AGN candidates. We focus on ZTF18aajyzfv: a luminous quasar offset by 6.7 $\pm$ 0.2 kpc from an adjacent galaxy at $z$=0.224, and conclude after Keck LRIS spectroscopy and comparison to ASTRID simulation analogs that it is likely a dual AGN. This selection method can be easily adapted to work with data from the soon-to-be commissioned Vera C. Rubin Telescope Legacy Survey of Space and Time (LSST). LSST will have a higher cadence and deeper magnitude limit than Pan-STARRS1, and should permit detection of many more runaway SMBH candidates.