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

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Abstract

  • 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 ? {{m}}, or {L}6? {{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}6? {{m}}/{10}45 erg s-1 (44.60 ± 0.01) for {L}6? {{m}}}}44.79 erg s-1, and {log}{L}{{X}}=(0.40 /- 0.03)× {log}{L}6? {{m}}/{10}45 erg s-1 (44.51 ± 0.01) for {L}6? {{m}} >=slant {10}44.79 erg s-1. This suggests that the luminous type 1 quasars have a shallower {L}{{X}}{--}{L}6? {{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}6? {{m}} relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasars.

Publication Date

  • 2017

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