OPTICAL-DETECTION OF THE HIDDEN NUCLEAR ENGINE IN NGC-4258

The subparsec masing disk recently found to be orbiting a central mass of similar to 3.6 x 10(7) M. in the Seyfert/LINER galaxy NGC 4258 (Mi yoshi and coworkers) provides the most compelling evidence to date for the existence of a massive black hole in the nucleus of a galaxy. The disk is oriented nearly edge-on, and the X-ray spectrum is heavily ab sorbed. Therefore, in this galaxy, the optical emission-line spectrum generally exhibited by an active galactic nucleus is perhaps best soug ht using polarized light: probing for light scattered off material sur rounding the central source. New polarimetry of NGC 4258 has uncovered a compact polarized nucleus whose spectrum consists of a faint blue c ontinuum similar to those of unobscured quasars (F-v proportional to v (-1.1)), plus broadened (similar to 1000 km s(-1)) emission lines. The lines are strongly linearly polarized (5%-10%) at a position angle (8 5 degrees +/- 2 degrees) coincident with the plane of the maser disk. This result provides substantiating evidence for a weakly active centr al engine in NGC 4258 and for the existence of obscuring, orbiting tor i, which impart many of the perceived distinctions between various typ es of active galaxies.