A Candidate Recoiling SMBH in a Local Active Galaxy?

Merging Supermassive Black Holes are a predicted key feature of models describing the co-evolution of galaxies and Active Galactic Nuclei (AGN). Following the merger, the SMBH is expected to undergo gravitational recoil velocities on the order of hundreds to thousands of km/s due to the anisotropic emission of gravitational radiation. Given that the majority of (massive) galaxies are thought to host a SMBH in the center, such events are expected to be relatively common. However, there have been only few candidates with no secure case so far. We present preliminary results of a recoiling SMBH candidate, discovered in a spectroscopic study of local AGNs selected from the SDSS. The SDSS image shows a blue knot offset from the center of the host galaxy by 1.5 arcsec, and SDSS fiber-spectra show asymmetric broad emission lines. Keck spectra centered on the host galaxy do not show broad lines; follow-up Lick spectroscopy associates AGN emission with the location of the blue knot. While these features are expected for a SMBH undergoing recoil, we discuss other possibilities such as a type IIn supernova or an ongoing merger.