THE DIFFERENCE IN NARROW Fe Kα LINE EMISSION BETWEEN SEYFERT 1 AND SEYFERT 2 GALAXIES

We compile a sample of 89 Seyfert galaxies with both [O IV] 25.89 mu m line luminosities observed by Spitzer IRS and X-ray spectra observed by XMM-Newton EPIC. Using [O IV] emission as a proxy for active galactic nucleus (AGN) intrinsic luminosity, we find that although type 2 AGNs have higher line equivalent widths, the narrow Fe K alpha lines in Compton-thin and Compton-thick Seyfert 2 galaxies are 2.9(-0.6)(+0.8) and 5.6(-1.4)(+1.9) times weaker in terms of luminosity than Seyfert 1 galaxies, respectively. This indicates that different correction factors need to be applied for various types of AGNs before the narrow Fe K alpha line luminosity could serve as an intrinsic AGN luminosity indicator. We also find that Seyfert 1 galaxies in our sample have on average marginally larger line widths and higher line centroid energies, suggesting contamination from highly ionized Fe line or broader line emission from much smaller radius, but this effect is too weak to explain the large difference in narrow Fe K alpha line luminosity between type 1 and type 2 AGNs. This is the first observational evidence showing that the narrow Fe K alpha line emission in AGNs is anisotropic. The observed difference is consistent with theoretical calculations assuming a smoothly distributed obscuring torus and could provide independent constraints on the clumpiness of the torus.