The Nature of the IR Emission in Low-Luminosity AGN at Parsec Scales

The vast majority of AGN belong to the low-luminosity class (LLAGN): they exhibit a low radiation efficiency (L/Ledd < 10^-3) and the absence of the big blue bump in their spectra, a signature of the accretion disk. The study of LLAGN is a complex task due to the contribution of the host galaxy, whose light outshines these faint nuclei. As a consequence, numerical models are usually compared with relatively poorly defined spectral energy distributions (SEDs). For a sample of six prototype nearby LLAGN, a multiwavelength dataset including radio, IR, optical/UV and X-ray measurements with subarcsec resolution has been collected. These high-spatial resolution SEDs reveal that: i) the mid-IR bump, indicative of thermal emission from the torus, is missing in LLAGN; ii) the continuum emission of these nuclei is largely described by a self-absorbed synchrotron spectrum, suggesting that compact jet emission dominates the overall energy output in LLAGN. In this scenario, the optically thin radiation in the IR-to-UV range is emitted at the jet launching region, very close to the central black hole.