THE PHYSICAL CHARACTERISTICS OF THE GAS IN THE DISK OF CENTAURUS A USING THEHERSCHEL SPACE OBSERVATORYJournal Articles
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abstract
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]$_{63}$)/$F_{TIR}$ 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.
