Origin of the Optical Polarization in the Nucleus of NGC 1068

Abstract

MEASUREMENTS of the degree of polarization of the nuclear region of NGC 1068 by Kruszewski¹ and Visvanathan and Oke² show that the degree of polarization increases with decreasing diaphragm size, which suggests that the polarization is produced in and close to the nucleus and that the radiation contributed by other parts of the galaxy is unpolarized. In order to find what process or processes are responsible for the optical radiation from the nucleus it is important to determine the intrinsic polarization of the nucleus. To do this we require the dilution factor, D, which is the ratio of the integrated surface brightness of all the radiation from the galaxy within the diaphragm to that of the nucleus. The distribution of surface brightness across the galaxy has been measured with a resolution of 2.6 square seconds by van Houten³; he has corrected the data for the smoothing introduced by finite angular resolution and by atmospheric dispersion to give a resolution of 1 square second. At this resolution the nucleus has a surface brightness S = 12^m_˙77 (square s)⁻¹; at r = 1 s, S = 16^m_˙35 (square s)⁻¹. Walker⁴ places an upper limit of 1.5 s on the nuclear diameter, 2r_N, corresponding to a nuclear area of 1.8 square s; we shall assume these values in what follows.