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

Chien Ting J. Chen, Ryan C. Hickox, Andrew D. Goulding, Daniel Stern, Roberto Assef, Christopher S. Kochanek, Michael J.I. Brown, Chris M. Harrison, Kevin N. Hainline, Stacey Alberts, David M. Alexander, Mark Brodwin, Agnese Del Moro, William R. Forman, Varoujan Gorjian, Christine Jones, Stephen S. Murray, Alexandra Pope, Emmanouel Rovilos

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39 Scopus citations


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.

Original languageEnglish (US)
Article number145
JournalAstrophysical Journal
Issue number2
StatePublished - Mar 10 2017


  • galaxies: active

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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