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Spatially resolving the innermost torus in AGN is one of the main goals ofits high-spatial-resolution studies. This could be done in the near-IRobservations of Type 1 AGNs where we see directly the hottest dust grains inthe torus. We discuss two critical issues in such studies. Firstly, we examinethe nuclear point sources in the HST/NICMOS images of nearby Type 1 AGNs, toevaluate the possible contribution from the central putative accretion disk.After a careful subtraction of host bulge flux, we show that near-IR colors ofthe point sources appear quite interpretable simply as a composite of ablack-body-like spectrum and a relatively blue distinct component as expectedfor a torus and an accretion disk, respectively. Our radiative transfer modelsfor clumpy tori also support this simple two-component interpretation. Theobserved near-IR colors suggest a fractional accretion disk contribution of~25% or less at 2.2 micron. Secondly, we show that the innermost torus radii asindicated by the recent near-IR reverberation measurements are systematicallysmaller by a factor of ~3 than the predicted dust sublimation radius with areasonable assumption for graphite grains of sublimation temperature 1500 K andsize 0.05 micron in radius. The discrepancy might indicate a much highersublimation temperature or a typical grain size being much larger in theinnermost tori, though the former case appears to be disfavored by the observedcolors of the HST point sources studied above. The near-IR interferometry witha baseline of ~100 m should be able to provide the important, independent sizemeasurements, based on the low accretion disk contribution obtained above.

The innermost region of AGN tori: implications from the HST/NICMOS Type 1 point sources and near-IR reverberation