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

Several recent studies have reported different intrinsic correlations between the active galactic nucleus (AGN) mid-IR luminosity ({L}_MIR}) and the rest-frame 2-10 keV luminosity (L _X) for luminous quasars. To understand the origin of the difference in the observed {L}_{{X}}{--}{L}_MIR} 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 {L}_{{X}}{--}{L}_MIR} 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 {L}_{{X}}{--}{L}_MIR} 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 6 μ {{m}}, or {L}_{6μ {{m}}}) of our sample of type 1 AGNs follow a bilinear relation in the log-log plane: {log}{L}_{{X}}=(0.84+/- 0.03)× {log}{L}_{6μ {{m}}}/{10}⁴⁵ erg s^-1 + (44.60 ± 0.01) for {L}_{6μ {{m}}}< {10}^44.79 erg s^-1, and {log}{L}_{{X}}=(0.40+/- 0.03)× {log}{L}_{6μ {{m}}}/{10}⁴⁵ erg s^-1 + (44.51 ± 0.01) for {L}_{6μ {{m}}} ≥slant {10}^44.79 erg s^-1. This suggests that the luminous type 1 quasars have a shallower {L}_{{X}}{--}{L}_{6μ {{m}}} correlation than the approximately linear relations found in local Seyfert galaxies. This result is consistent with previous studies reporting a luminosity-dependent {L}_{{X}}{--}{L}_MIR} relation and implies that assuming a linear {L}_{{X}}{--}{L}_{6μ {{m}}} relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasars.