NGC 1068 - Resolution of nuclear structure in the optical continuum

Abstract

An optical continuum image of the Seyfert galaxy NGC 1068 has been obtained with the Planetary Camera on the Hubble Space Telescope as part of the SAO/ERO program. The filter used, F547M, has an effective wavelength and a width of approximately 5470 and 650 A and excludes all discrete emission lines that might be present. The point-spread function, although compromised by the aberrations of the telescope optics, does permit significant response at the 0".1 resolution originally anticipated. Deconvolution of the image for the effects of the point-spread function reveals a bright nucleus embedded in an irregular cloudlike structure which is well differentiated against the background of the galaxy. The nucleus is resolved, with a FWHM of ~0".15, or 11 pc and there is no evidence for any unresolved nuclear component. The lack of an unresolved point source is consistent with the picture in which the broad-line region is seen indirectly via electron scattering, but the precise geometry of the scattering region cannot yet be inferred. The cloud surrounding the nucleus is elongated in the NE-SW direction and has extreme dimensions of 3".5 x 1".7 (255 x 124 pc). Although the extent of the cloud is roughly centered on the nucleus, its brightness centroid is situated 0".4 southwest of the nucleus. Because of the relative photometric dominance of the cloud with respect to both the nucleus and the underlying galaxy and the corresponding dominance of unpolarized star light found by Antonucci and Miller, the conclusion seems inescapable that the light from the cloud is contributed largely by stars. But in appearance the cloud is distinctly dissimilar to our expectation for either young or old stellar systems, and it seems to bear no simple relationship to the numerous features that have heretofore been resolved at other optical, infrared, and radio wavelengths. A determination of the true nature of both the cloud and the nuclear feature through spectroscopic and polarimetric measurements is of the highest priority.