A diversity of dusty AGN tori

Context. The AGN-heated dust distribution (the “torus”) is increasingly recognized not only as the absorber required in unifying models, but as a tracer for the reservoir that feeds the nuclear super-massive black hole. Yet, even its most basic structural properties (such as its extent, geometry and elongation) are unknown for all but a few archetypal objects. Aims. In order to understand how the properties of AGN tori are related to feeding and obscuration, we need to resolve the matter distribution on parsec scales. Methods. Since most AGNs are unresolved in the mid-IR, even with the largest telescopes, we utilize the MID-infrared interferometric Instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) that is sensitive to structures as small as a few milli-arcseconds (mas). We present here an extensive amount of new interferometric observations from the MIDI AGN Large Program (2009–2011) and add data from the archive to give a complete view of the existing MIDI observations of AGNs. Additionally, we have obtained high-quality mid-IR spectra from VLT/VISIR to provide a precise total flux reference for the interferometric data. Results. We present correlated and total fluxes for 23 AGNs (16 of which with new data) and derive flux and size estimates at 12 μm using simple axisymmetric geometrical models. Perhaps the most surprising result is the relatively high level of unresolved flux and its large scatter: The median “point source fraction” is 70% for type 1 and 47 % for type 2 AGNs meaning that a large part of the flux is concentrated on scales