The Physical Characteristics of the Gas in the Disk of Centaurus A Using the Herschel Space Observatory
Boquien, M.; Roussel, H.; Lebouteiller, V.; Madden, S. C.; De Looze, I.; Cormier, D.; Galametz, M.; Wilson, C. D.; Baes, M.; Boselli, A.; Spinoglio, L.; Smith, M. W. L.; Karczewski, O. Ł.; Parkin, T. J.; Schirm, M. R. P.
Canada, Belgium, France, Germany, United Kingdom, Italy
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 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)/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 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.
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.