FAINT OBJECT CAMERA IMAGING AND SPECTROSCOPY OF NGC-4151

We describe ultraviolet and optical imaging and spectroscopy within th e central few arcseconds of the Seyfert galaxy NGC 4151, obtained with the Faint Object Camera on the Hubble Space Telescope. A narrowband i mage including [O III] lambda 5007 shows a bright nucleus centered on a complex biconical structure having apparent opening angle similar to 65 degrees and axis at position angle along 65 degrees-245 degrees; i mages in bands including Lyman-alpha and CIV lambda 1550 and in the op tical continuum near 5500 Angstrom, show only the bright nucleus. In a n off-nuclear optical long-slit spectrum we find a high and a low radi al velocity component within the narrow emission lines. We identify th e low-velocity component with the bright, extended, knotty structure w ithin the cones, and the high-velocity component with more confined di ffuse emission. Also present are strong continuum emission and broad B almer emission line components, which we attribute to the extended poi nt spread function arising from the intense nuclear emission. Adopting the geometry pointed out by Pedlar et al. (1993) to explain the obser ved misalignment of the radio jets and the main optical structure we m odel an ionizing radiation bicone, originating within a galactic disk, with apex at the active nucleus and axis centered on the extended rad io jets. We confirm that through density bounding the gross spatial st ructure of the emission line region can be reproduced with a wide open ing angle that includes the line of sight, consistent with the presenc e of a simple opaque torus allowing direct view of the nucleus. In par ticular, our modelling reproduces the observed decrease in position an gle with distance from the nucleus, progressing initially from the dir ection of the extended radio jet, through our optical structure, and o n to the extended narrow-line region. We explore the kinematics of the narrow-line low- and high-velocity components on the basis of our spe ctroscopy and adopted model structure. For the low-velocity system bot h Keplerian rotation and isotropic outflow (or outflow confined to the ionizing cone) give plausible correspondence with our data. If interp reted as rotation we show consistency with earlier determinations indi cating a central mass concentration of about 10(9) M.. The high-veloci ty system kinematically conforms to radial outflow within the galaxy d isk, although this does not well reproduce the observed intensity stru cture.