Publications of the MPIfR
Optical & Infrared
Interferometry Group
A. Boksenberg, R.M. Catchpole, R.
Albrecht, C. Barbieri, J.C. Blades, A. Boksenberg, J.M. Deharveng, M.J.
Disney, M.J. Jakobsen, T.M. Kamperman, I.R. King, F. Macchetto, C.D.
Mackay, F. Paresce, G. Weigelt, P. Greenfield, R. Jedrzejewski, and A.
Nota
Faint Object Camera Imaging and Spectroscopy of
NGC 4151
The Astrophysical Journal, v.440, p.151 (1995)
Abstract
We describe ultraviolet and optical imaging and spectroscopy within the
central few arcseconds of the Seyfert galaxy NGC 4151, obtained with
the
Faint Object Camera on the Hubble Space Telescope. A narrowband image
including (O III) lambda(5007) shows a bright nucleus centered on a
complex biconical structure having apparent opening angle approximately
65 deg and axis at a position angle along 65 deg-245 deg; images in
bands including Lyman-alpha and C IV lambda(1550) and in the optical
continuum near 5500 A, show only the bright nucleus. In an off-nuclear
optical long-slit spectrum we find a high and a low radial velocity
component within the narrow emission lines. We identify the
low-velocity
component with the bright, extended, knotty structure within the cones,
and the high-velocity component with more confined diffuse emission.
Also present are strong continuum emission and broad Balmer emission
line components, which we attribute to the extended point spread
function arising from the intense nuclear emission. Adopting the
geometry pointed out by Pedlar et al. (1993) to explain the observed
misalignment of the radio jets and the main optical structure we model
an ionizing radiation bicone, originating within a galactic disk, with
apex at the active nucleus and axis centered on the extended radio
jets.
We confirm that through density bounding the gross spatial structure of
the emission line region can be reproduced with a wide opening angle
that includes the line of sight, consistent with the presence of a
simple opaque torus allowing direct view of the nucleus. In particular,
our modelling reproduces the observed decrease in position angle with
distance from the nucleus, progressing initially from the direction of
the extended radio jet, through our optical structure, and on to the
extended narrow-line region. We explore the kinematics of the
narrow-line low- and high-velocity components on the basis of our
spectroscopy and adopted model structure.
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