OBSERVABILITY OF DUAL ACTIVE GALACTIC NUCLEI IN MERGING GALAXIES

Abstract

Supermassive black holes (SMBHs) have been detected in the centers of most\nnearby massive galaxies. Galaxies today are the products of billions of years\nof galaxy mergers, but also billions of years of SMBH activity as active\ngalactic nuclei (AGNs) that is connected to galaxy mergers. In this context,\ndetection of AGN pairs should be relatively common. Observationally, however,\ndual AGN are scant, being just a few percent of all AGN. In this Letter we\ninvestigate the triggering of AGN activity in merging galaxies via a suite of\nhigh resolution hydrodynamical simulations. We follow the dynamics and\naccretion onto the SMBHs as they move from separations of tens of kiloparsecs\nto tens of parsecs. Our resolution, cooling and star formation implementation\nproduce an inhomogeneous, multi-phase interstellar medium, allowing us to\naccurately trace star formation and accretion onto the SMBHs. We study the\nimpact of gas content, morphology, and mass ratio, allowing us to study AGN\nactivity and dynamics across a wide range of relevant conditions. We test when\nthe two AGN are simultaneously detectable, for how long and at which\nseparations. We find that strong dual AGN activity occurs during the late\nphases of the mergers, at small separations (<1-10 kpc) below the resolution\nlimit of most surveys. Much of the SMBH accretion is not simultaneous, limiting\nthe dual AGN fraction detectable through imaging and spectroscopy to a few\npercent, in agreement with observational samples.\n