THE PHYSICAL CHARACTERISTICS OF THE GAS IN THE DISK OF CENTAURUS A USING THE HERSCHEL SPACE OBSERVATORY**Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

We search for variations in the disk of Centaurus A of the emission from atomic fine structure lines using Herschel PACS and SPIRE spectroscopy. In particular, we observe the [C ii](158 μm), [N ii](122 and 205 μm), [O i](63 and 145 μm), and [O iii](88 μm) lines, which all play an important role in cooling the gas in photo-ionized and photodissociation regions (PDRs). We determine that the ([C ii]+[O i]63)/FTIR line ratio, a proxy for the heating efficiency of the gas, shows no significant radial trend across the observed region, in contrast to observations of other nearby galaxies. We determine that 10%–20% of the observed [C ii] emission originates in ionized gas. Comparison between our observations and a PDR model shows that the strength of the far-ultraviolet radiation field, G0, varies between 101.75 and 102.75 and the hydrogen nucleus density varies between 102.75 and 103.75 cm−3, with no significant radial trend in either property. In the context of the emission line properties of the grand-design spiral galaxy M51 and the elliptical galaxy NGC 4125, the gas in Cen A appears more characteristic of that in typical disk galaxies rather than elliptical galaxies.