High Spatial Resolution Mid-Infrared Observations of Three Seyfert Galaxies

Images at 12.5 μm of nuclei of three nearby Seyfert galaxies-NGC 1275, NGC 4151, and NGC 7469-have been obtained with the 10 m Keck Telescope. NGC 7469 is resolved and deconvolution delineates a structure (<0.04")×0.08", or less than 13×26 pc at a position angle of 135°. From a comparison with structure seen at millimeter wavelengths, this structure is interpreted as a disk aligned with the molecular gas in the central few hundred parsecs of the galaxy. NGC 1275 and NGC 4151 are not resolved; limits on the sizes of these nuclei are 0.08" and 0.16", corresponding to physical spatial scales of 28 and 10 pc. The lower limits to the brightness temperatures implied by these size limits and the measured flux densities are within ~50 K of the 12-25 μm color temperatures of these systems, as inferred from IRAS observations. The angular size limits are within a factor of 2 of the sizes required to spatially resolve thermal emission from dust heated by a central luminosity source. These sizes preclude significant contributions to the nuclear infrared emission from star-forming regions.