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.

TWO-DIMENSIONAL MAPPING OF YOUNG STARS IN THE INNER 180 pc OF NGC 1068: CORRELATION WITH MOLECULAR GAS RING AND STELLAR KINEMATICS

“…In spite of its proximity, there is only limited information about the stellar population in the vicinity of its active nucleus. Lynds et al (1991) reported a high contrast structure surrounding the nucleus in a Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 (WFPC2) optical image of NGC 1068 in the continuum (centered at 5470 Å) interpreted as a stellar cluster. Thatte et al (1997) reported the detection of this stellar cluster from stellar CO absorption features in the H-and K-band spectra and estimated its size as FWHM ≈ 50 pc and age in the range 5-16 × 10 8 yr. Crenshaw & Kraemer (2000) have analyzed two long-slit spectra obtained with the HST Imaging Spectrograph (STIS) covering the inner ∼500 pc in the wavelength range 1150-10270 Å.…”

Resolved Spectroscopy of the Narrow‐Line Region in NGC 1068. I. The Nature of the Continuum Emission

“…-4 - Lynds et al (1991) suggest that this extended region is dominated by stellar light, but that polimetry and/or spectroscopy are needed for verification. By contrast, HST images of the UV continuum emission resemble those of the emission lines, and in particular, show that the hot spot and a conical region NE of it are bright in the UV (Kriss et al 1993;Macchetto et al 1994).…”

Diffraction-limited Imaging and Photometry of NGC 1068

“…At scales of a few hundred parsecs around the nucleus, Hubble Space T elescope (HST ) narrowband (Macchetto et al 1994) and continuum (Lynds et al 1991) imaging show a nonuniform conical narrow-line region. These observations suggest that clumps of gas have been ionized by a partially collimated nuclear source.…”