Several recent studies have reported different intrinsic correlations between the active galactic nucleus (AGN) mid-IR luminosity (LMIR) and the rest-frame 2-10 keV luminosity (LX) for luminous quasars. To understand the origin of the difference in the observed LX-LMIR 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 LX-LMIR 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 LX-LMIR 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 μm, or L6 μm) of our sample of type 1 AGNs follow a bilinear relation in the log-log plane: log LX = (0.84 ± 0.03) × log L6 μm 1045 erg s-1 + = (44.60 ± 0.01) for L6 μ <1044.79 erg s-1, and log LX = (0.40±0.03) × log L6 μm/1045 + erg s-1 +(44.51 ± 0.01) for L6 μm ≥ 1044.79 erg s-1. This suggests that the luminous type 1 quasars have a shallower LX-L6 μm correlation than the approximately linear relations found in local Seyfert galaxies. This result is consistent with previous studies reporting a luminosity-dependent LX-LMIR relation and implies that assuming a linear LX-L6 μm relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasars.
- galaxies: active