The X-Ray and Mid-infrared Luminosities in Luminous Type 1 Quasars

Abstract

Abstract Several recent studies have reported different intrinsic correlations between the active galactic nucleus (AGN) mid-IR luminosity ( ) and the rest-frame 2–10 keV luminosity ( L X ) for luminous quasars. To understand the origin of the difference in the observed relations, we study a sample of 3247 spectroscopically confirmed type 1 AGNs collected from Boötes, XMM -COSMOS, XMM -XXL-North, and the Sloan Digital Sky Survey quasars in the Swift /XRT footprint spanning over four orders of magnitude in luminosity. We carefully examine how different observational constraints impact the observed relations, including the inclusion of X-ray-nondetected objects, possible X-ray absorption in type 1 AGNs, X-ray flux limits, and star formation contamination. We find that the primary factor driving the different relations reported in the literature is the X-ray flux limits for different studies. When taking these effects into account, we find that the X-ray luminosity and mid-IR luminosity (measured at rest-frame , or ) of our sample of type 1 AGNs follow a bilinear relation in the log–log plane: erg s −1 + (44.60 ± 0.01) for erg s −1 , and erg s −1 + (44.51 ± 0.01) for erg s −1 . This suggests that the luminous type 1 quasars have a shallower correlation than the approximately linear relations found in local Seyfert galaxies. This result is consistent with previous studies reporting a luminosity-dependent relation and implies that assuming a linear relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasars.