A MIDINFRARED TEST OF THE OBSCURING TORUS MODEL FOR SEYFERT NUCLEI

Ground-based small-aperture measurements of the nuclear and mid-infrared emission (in the N band at 10.6 mu m) are considered for a large but heterogeneous sample of Seyfert galaxies, and also for three smaller but homogeneous samples (one far-infrared-selected, one mid-infrared-selected, and one optically selected). For all these samples, the average ratio of 10.6 mu m to nonthermal radio continuum (1.4 GHz) flux densities is similar to 4 times larger in the type 1 Seyferts than in the type 2 Seyferts (at high levels of statistical significance). Also, the average ratio of the 10.6 mu m flux density to the [O III] lambda 5007 emission-line flux is about twice as large in type 1 Seyferts compared to type 2 Seyferts, although this difference is of high statistical significance only in the large heterogeneous sample. These results are similar to the differences in the mid-infrared between the quasars and broad-line radio galaxies compared to the narrow-line radio galaxies in the 3CR catalog. All these results are in satisfactory agreement with the predictions for mildly anisotropic thermal mid-infrared emission from the optically thick ''obscuring torus'' that is hypothesized to be responsible for hiding the type 1 Seyfert nucleus (quasar) from our direct view in type 2 Seyfert galaxies (narrow-line radio galaxies).