High-Resolution Mid-Infrared Images of the Nucleus of M81

We observed two nearby galaxies with potential or weak indications of nuclear activity, M32 and M81, with the MIRLIN mid-IR camera at N band (10.79 μm). M32 is not detected, but we give detailed measurements of the nucleus of M81. Our observations of M81 show a bright nuclear point source at N, and comparison to measurements made in the early 1970s gives an increase in nuclear flux of nearly a factor of 2. If the comparison is accurate, the nuclear mid-IR emission must ultimately be powered by a variable, compact source, similar to that in Seyfert galaxies and quasars. M81 has been classified in the literature as a low-luminosity LINER, not a pure Seyfert galaxy. Further, it has been suggested that this and other low-luminosity active galactic nuclei may have intrinsically different spectra than Seyfert galaxies and quasars. However, we find that the relative fluxes in the X-ray, mid-IR, and radio bands, all essentially unaffected by extinction and galaxy pollution, show a nuclear continuum remarkably like that of a bona fide Seyfert galaxy or quasar.