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 Bootes, 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 mu m, or L-6 mu m) of our sample of type 1 AGNs follow a bilinear relation in the log-log plane: log L-X = (0.84 +/- 0.03) logL(6) (mu m) /10(45)erg s(-1) + (44.60. +/- 0.01) for L-6 (mu m) < 10(44.79) erg s(-1), and log L-X (0.40 +/- 0.03) log L-6 (mu m)/10(45) erg s(-1) + (44.51 +/- 0.01) for L-6 mu m. 1044.79 erg s(-1). This suggests that the luminous type 1 quasars have a shallower LX-L6mmcorrelation than the approximately linear relations found in local Seyfert galaxies. This result is consistent with previous studies reporting a luminosity-dependent LX-LMIRrelation and implies that assuming a linear LX-L-6 mu m relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasars.