S.J. Unger 1, P.E. Clegg 1, P. Cox 2, J. Fischer 3, M. Greenhouse 4, S. D. Lord 5, M. L. Luhman 3, M. A. Malkan 6, S. Satyapal 4, H.A. Smith 7, L. Spinoglio 8, G. J. Stacey 9, & M. Wolfire 10
1 Queen Mary and Westfield College, London, UK
2 Institut d'Astrophysicque Spatiale, France
3 Naval Research Laboratory, Washington, USA
4 NASA Goddard, Greenbelt, USA
5 California Institute of Technology, Pasadena, USA
6 University of California, Los Angeles, USA
7 Smithsonian Astrophysical Observatory, Cambridge, USA
8 Istituto di Fisica dello Spazio Interplanetario-CNR, Frascati, Italy
9 Cornell University, Ithaca, NY, USA
10 University of Maryland, College Park, USA
Centaurus A (NGC 5128) is our closest active radio galaxy at a
distance of 3.5 Mpc. UV photons (6 eV < h
13.6 eV) from
either O/B stars or
an AGN will photodissociate H2 and CO molecules and photoionize
elements with ionization potentials less than the Lyman limit
(e.g. C+ ionization potential = 11.26 eV). The gas heating in these
photodissociation regions (PDRs) is dominated by electrons ejected from
grains due to the photoelectric effect. Gas cooling is dominated by the
emission of [O I ] 63 
m and [C II ] 158 m emission.
We observed Cen A with the Long Wavelength Spectrometer (LWS) in the low
resolution grating mode (
). A
full grating observation (43 to 197m) was taken at the location of
the blazar and the [O I ] 63 m, [O I ] 145m and [C II ] 158 m
lines were observed at two additional positions in the dust lane.
The relative strengths of these lines in combination with a measure of the FIR continuum and CO (J=1-0) 2.6 mm line (taken from the literature) are used to model the average physical properties of the PDRs.