Session 21 - Luminous Infrared Galaxies.
Display session, Wednesday, January 07
Exhibit Hall,

## [21.05] ISO LWS Spectroscopy of NGC 4945

J. Brauher, S. Lord, S. Unger (IPAC), M. Wolfire (U. Maryland; Towson U.), J. Fischer (NRL)

We have obtained fully sampled, low resolution (R=\lambda/ \triangle \lambda \sim 200) far-infrared (FIR) 42-197 \mum spectra of the southern AGN/starburst SB(s)cd galaxy NGC 4945 with the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). The galaxy was observed at a central, NE, and SW position, each separated by 165'' with the instrument's \sim 75" aperture. The forbidden fine-structure transitions of [CII] 158 \mum and [OI] 63 \mum lines were detected at each position. Detections of the [OI] 145 \mum and [OIII] 88 \mum lines were also obtained at some positions. Using these lines and the total FIR continuum flux, we have modeled the properties of the warm atomic gas with photodissociation region (PDR) models (Tielens and Hollenbach, 1985; Wolfire et al. 1990; Kaufman et al. 1998). The low-J rotational transitions of OH at 53 \mum and 119 \mum are seen in absorption at the nuclear position. The total OH column density and the role of these lines in the pumping of the OH radio maser are considered for these two transitions. The NE and SW positions lie on the massive molecular ring. The ring versus the nuclear conditions are analyzed by comparing the CII/OI, CII/CO, and (CII+OI)/FIR ratios.