[C ii] 158 μm LUMINOSITIES AND STAR FORMATION RATE IN DUSTY STARBURSTS AND ACTIVE GALACTIC NUCLEI

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 Lir 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 Lir 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 Lir in more luminous sources (the “[C ii] deficit”) is shown to be a consequence of the dominant contribution to Lir arising from a luminous AGN component because the sources with the largest Lir and smallest L([C ii])/Lir are AGNs.