CALIBRATION OF [O IV] 26 μm AS A MEASURE OF INTRINSIC ACTIVE GALACTIC NUCLEUS LUMINOSITY

We compare [O iv ] 25.89 μm emission line luminosities with very hard (10–200 keV) X-rays from Swift , INTEGRAL , and BeppoSAX for a complete sample of 89 Seyferts from the Revised Shapley–Ames sample. Using Seyfert 1s, we calibrate [O iv ] as a measure of active galactic nucleus (AGN) intrinsic luminosity, for particular use in high-obscuration environments. With this calibration, we measure the average decrement in 14–195 keV X-ray to [O iv ] luminosity ratio for Seyfert 2s compared to type 1s. We find a decrement of 3.1 ± 0.8 for Seyfert 2s, and a decrement of 5.0 ± 2.7 for known Compton-thick Seyfert 2s. These decrements imply column densities of approximately log N H = 24.6 cm −2 and 24.7 cm −2 , respectively. Thus, we infer that the average Seyfert 2 is more highly obscured and intrinsically more luminous than would be inferred even from the very hard X-rays. We demonstrate two applications of the hard X-ray to [O iv ] ratio. For the extremely obscured NGC 1068, we measure a column density of log N H = 25.3–25.4 cm −2 . Finally, by comparing [O iv ] luminosities to total infrared luminosities for 12 bright ultraluminous infrared galaxies, we find that four have substantial AGN contributions.