The Millimeter/X-Ray Relation in Rapidly Accreting Supermassive Black Holes at z < 0.16

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Abstract
A tight correlation between nuclear millimeter and X-ray emission has recently been found in nearby ( z < 0.01) and low-Eddington ratio ( λ Edd < 0.1) radio-quiet active galactic nuclei (AGNs), suggesting a common origin in the hot X-ray corona. We test this relation in nine more distant AGNs ( z ∼ 0.06–0.16) with higher bolometric luminosities ( log ( L bol / erg s − 1 ) = 45.3 –46.3), Eddington ratios ( λ Edd = 0.19–0.85), and X-ray bolometric corrections ( κ = 29–194), selected from the Burst Alert Telescope (BAT) survey. We obtained observations with Swift at 2–10 keV and quasi-simultaneous observations with the Atacama Large Millimeter/submillimeter Array at 100 GHz with high angular resolution ( . ″ 14 arcsec). We find that these high-luminosity AGNs lie above the millimeter/X-ray correlation defined by lower-luminosity sources. A joint fit to both samples yields a second-degree polynomial with an intrinsic scatter of 0.32 dex. Furthermore, the millimeter emission correlates linearly with both the UV disk luminosity and L bol , with intrinsic scatters of 0.45 and 0.35 dex, respectively. We propose that the deviation from the linear millimeter/X-ray relation arises from a two-component coronal electron population: thermal electrons that produce X-rays, but become less efficient at higher luminosities, and nonthermal electrons that produce millimeter emission and remain tied to L bol . Additional millimeter emission from outflow-driven shocks may also contribute, though spectral energy distribution modeling and spectral index studies favor a coronal origin.
Funding Information
  • ANID ∣ Fondo Nacional de Desarrollo Científico y Tecnológico (1230345)

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