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 \mu m ) , [ N ii ] ( 122 and 205 \mu m ) , [ O i ] ( 63 and 145 \mu m ) and [ O iii ] ( 88 \mu m ) lines , which all play an important role in cooling the gas in photo-ionized and photodissociation regions .
We determine that the ( [ C ii ] + [ O i ] _ { 63 } ) / F _ { \mathrm { TIR } } 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 , G _ { 0 } , varies between 10 ^ { 1.75 } and 10 ^ { 2.75 } and the hydrogen nucleus density varies between 10 ^ { 2.75 } and 10 ^ { 3.75 } 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 .