Results are presented for [C II] 158 μm line fluxes observed with the Herschel PACS instrument in 112 sources with both starburst and active galactic nucleus (AGN) classifications, of which 102 sources have confident detections. Results are compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and with L ir from IRAS fluxes; AGN/starburst classifications are determined from equivalent width of the 6.2 μm polycyclic aromatic hydrocarbon (PAH) feature. It is found that the [C II] line flux correlates closely with the flux of the 11.3 μm PAH feature independent of AGN/starburst classification, log [f([C II] 158 μm)/f(11.3 μm PAH)] = –0.22 ± 0.25. It is concluded that the [C II] line flux measures the photodissociation region associated with starbursts in the same fashion as the PAH feature. A calibration of star formation rate (SFR) for the starburst component in any source having [C II] is derived comparing [C II] luminosity L([C II]) to L ir with the result that log SFR = log L([C II)]) – 7.08 ± 0.3, for SFR in M ☉?yr–1 and L([C II]) in L ☉. The decreasing ratio of L([C II]) to L ir in more luminous sources (the "[C II] deficit") is shown to be a consequence of the dominant contribution to L ir arising from a luminous AGN component because the sources with the largest L ir and smallest L([C II])/L ir are AGNs.
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