Abstract

We show that resolved mid-infrared (mid-IR) imaging of active galactic nuclei (AGN) is an isotropic probe of their intrinsic luminosities. We have obtained the largest sample to date of 8-m telescope diffraction-limited mid-IR imaging of radio-quiet AGN (42 sources so far), using which we find a strong correlation between mid-IR (12 micron) and intrinsic X-ray (2-10 keV) luminosities. The relation holds true for Seyferts of all types, including unobscured, obscured, as well as heavily Compton-thick sources. Thus, the mid-IR directly probes the intrinsic accretion power irrespective of obscuration, and provides a new and accurate proxy of AGN luminosity (complementing other tools such as the forbidden [OIII]5007 emission line). The relation may also be extended smoothly to the higher luminosity quasar regime. Most star formation around the nuclei is resolved out, and the remaining unresolved mid-IR flux is dominated by the AGN alone. This enables clean estimates of bolometric luminosities to be derived for the first time. The dispersion in the mid-IR:X-ray relation is tight enough to provide sensitive discrimination between physical models of clumpy vs. smooth dusty tori geometries. In addition, our relation also provides a simple pathway for estimating the intrinsic powers of Compton-thick AGN .