Speckle Imaging of the Nuclei of Six Seyfert Galaxies at Wavelengths of 2.2 Micron and 1.6 Micron

Six Seyfert galaxies were observed with speckle imaging techniques in the near-infrared H-band (1.6 μ m) and K-band (2.2 μ m). Observations of all the sources, NGC 1068, MRK 231, NGC 3227, NGC 4151, NGC 5506, and NGC 7469, were made at the Palomar 200-inch Telescope and K-band observations of NGC 1068 were also made with the 10-m W. M. Keck Telescope. Images with diffraction limited or near-diffraction limited resolutions of 0./prime' 05[-]0./prime/prime15 were obtained and used to search for structure in the nuclear regions. Images of the nucleus of NGC 1068 reveal an extended region of emission which accounts for nearly 50% of the nuclear flux at K-band. This region extends 10 pc on either side of an unresolved point source nucleus which is at most, 0./prime' 03 or 2 pc in size. Both the point source and the newly revealed extended emission are very red, with identical H-K colors corresponding to a color temperature of 800 K. While the point source is of a size to be consistent with grains in thermal equilibrium with the nuclear source, the extended emission is not. It must either be comprised of nuclear emission which has been reflected off an extended dusty disk or of small grains raised to transiently high temperatures by reflected UV photons. Images of the nuclear region of the Seyfert 1.5 galaxy NGC 3227 also show an unresolved point source which is at most 0.^/prime'02 (1.5 pc) in size as well as an extended region. In H-K color, however, the nucleus is much redder than the extended source and is consistent with emission from grains in thermal equilibrium with the central luminosity source. The bluer extended source is likely to be a continuation of the known bright central stellar cluster. Extended L_s-band emission imaged at 70-250 pc from the nucleus is also likely to arise from stars. Speckle measurements of the other four galaxies are used to place upper limits on the sizes of their unresolved cores. In each, the size of the nuclear emission is consistent with near-infrared flux emitted from grains in thermal equilibrium with the central luminosity source.