HST NICMOS Observations of the Polarization of NGC 1068

Abstract

We have observed the polarized light at 2 micron in the center of NGC 1068 with HST NICMOS Camera 2. The nucleus is dominated by a bright, unresolved source, polarized at a level of 6.0 pm 1.2% with a position angle of 122degr pm 1.5degr. There are two polarized lobes extending up to 8'' northeast and southwest of the nucleus. The polarized flux in both lobes is quite clumpy, with the maximum polarization occurring in the southwest lobe at a level of 17% when smoothed to 0.23'' resolution. The perpendiculars to the polarization vectors in these two lobes point back to the intense unresolved nuclear source to within one 0.076'' Camera 2 pixel, thereby confirming that this is the illuminating source of the scattered light and therefore the probable AGN central engine. Whereas the polarization of the nucleus is probably caused by dichroic absorption, the polarization in the lobes is almost certainly caused by scattering, with very little contribution from dichroic absorption. Features in the polarized lobes include a gap at a distance of about 1'' from the nucleus toward the southwest lobe and a ``knot'' of emission about 5'' northeast of the nucleus. Both features had been discussed by ground-based observers, but they are much better defined with the high spatial resolution of NICMOS. The northeast knot may be the side of a molecular cloud that is facing the nucleus, which cloud may be preventing the expansion of the northeast radio lobe at the head of the radio synchrotron-radiation-emitting jet. We also report the presence of two ghosts in the Camera 2 polarizers. These had not been detected previously (Hines et al. 2000) because they are relatively faint and require observations of a source with a large dynamic range.