Today's Colloquium: Seeing double - looking for dual active galactic nuclei with VLBI

Image may be NSFW.
Clik here to view.© Sandor Frey

Supermassive black holes (SMBHs) in the centres of large galaxies seem ubiquitous in the Universe. If interactions and mergers indeed play a significant role in galaxy evolution, then the growth of the central SMBHs should also be affected. We expect to witness different stages of the merging process by means of detecting nuclear activity driven by accretion onto the pairs of SMBHs. However, finding dual active galactic nuclei (AGN) with kpc-scale or smaller separations is not an easy task observationally. There are relatively few convincing (spatially resolved) cases reported in the literature. I briefly review how dual AGN are searched for, what are the promises and the difficulties, and how the fine angular resolution of radio interferometry could help in this endeavour. As an illustration, I show results from a couple of our recent VLBI experiments targeting dual AGN candidates. For the time being, the conclusion in short: an efficient selection method to find kpc-scale dual radio AGN is yet to be invented.

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