A search for broad infrared recombination lines in NGC 1068
D. Lutz, R. Genzel, E. Sturm, L. Tacconi,
E. Wieprecht, T. Alexander,
H. Netzer, A. Sternberg, A.F.M. Moorwood, R.A.E. Fosbury,
K. Fricke, S.J. Wagner, A. Quirrenbach, H. Awaki,
K.Y. Lo
Abstract:
We report infrared spectroscopy of the prototypical Seyfert 2 galaxy NGC
1068,
aiming at detection of broad components of hydrogen recombination lines
that originate in the obscured broad-line region. Using the Short
Wavelength
Spectrometer on board the Infrared Space Observatory, we have observed
for
the first time the regions of Brackett beta 2.626µm and
Pfund alpha 7.460µm, and
present improved data for Brackett alpha 4.052µm.
No significant
broad
components are detected, implying an equivalent visual extinction
to the broad-line region of at least 50 magnitudes and an obscuring
column density of at least 1023cm-2. While consistent
with a highly obscured broad-line region, as required by the classical
unified
scenario, these limits are not yet
significant enough to discriminate strongly between different torus
models or
to constrain properties of the gas causing the very large X-ray
obscuration.
We discuss the systematic limitations of infrared broad-line region
searches
and suggest that Brackett alpha may often be the most favorable
transition
for future searches.
Keywords: galaxies: individual (NGC 1068) --- galaxies:
Seyfert --- infrared: ISM: lines and bands
Status: ApJ accepted
Address: mailto:
lutz@mpe.mpg.de
Full text
(PostScript file)
MPE Home Page |
IR/SubMM Department |
ISO Data Centre |
ISO Preprints
Last update: 07-Oct-1999 by K.Seidenschwang
mailto:
isodata@mpe.mpg.de