Active Galactic Nuclei in Nearby Galaxies

A large fraction of nearby Galaxies, including our own, show evidence for low-level activity associated with accretion onto a supermassive black hole. This allows one to study black hole physics at accretion rates significantly below those inferred for quasars and Seyfert galaxies. A major issue is whether the mode of accretion changes when going to sub-Eddington luminosities. Interestingly, radio surveys of Low-Luminosity AGN (LLAGN) find a high number of compact radio cores with flat spectra and high brightness temperatures. These are similar to those in radio loud quasars, albeit at a much lower luminosity. In the optical, on the other hand, LLAGN look markedly different from quasars and Seyfert, with relatively faint optical/UV continuum emission. One can model the overall spectral energy distribution of LLAGN from radio to X-rays with a combination of jet-like outflows and optically thin accretion flows. Data and models suggest that the overall appearance of black holes becomes increasingly jet-dominated as one decreases the accretion rate. Hence, radio will be a prime method for studying these kind of AGN. In addition, because of the proximity of LLAGN, the next generation radio telescopes (EVLA, SKA, ALMA + VLBI) will be able to approach the event horizon of the central black holes. Using the LLAGN as a reference point, one can also make proper motion studies of entire galaxies within a few Mpc.