Infrared Contributions of X-Ray Selected Active Galactic Nuclei in Dusty Star-forming Galaxies

Abstract

Abstract We investigate the infrared (IR) contribution from supermassive black hole activity versus host galaxy emission in the mid- to far-IR spectrum for a large sample of X-ray bright active galactic nuclei (AGN) residing in dusty, star-forming host galaxies. We select 703 AGN with erg s−1 at 0.1 < z < 5 from the Chandra XBoötes X-ray Survey with rich multiband observations in the optical to far-IR. This is the largest sample to date of X-ray AGN with mid- and far-IR detections that uses spectral energy distribution (SED) decomposition to determine intrinsic AGN and host galaxy IR luminosities. We determine weak or nonexistent relationships when averaging star formation activity as a function of AGN activity, but see stronger positive trends when averaging L X in bins of star-forming activity for AGN at low redshifts. We estimate an average dust covering factor (CF) of 33% based on IR SEDs and bolometric AGN luminosity, corresponding to a Type 2 AGN population of roughly a third. We also see a population of AGN that challenge the inclination-based unification model with individual dust CFs that contradict the nuclear obscuration expected from observed X-ray hardness ratios. We see no strong connection between AGN fractions in the IR and corresponding total IR, 24 μm, or X-ray luminosities. The average rest-frame AGN contribution as a function of IR wavelength shows significant (∼80%) contributions in the mid-IR that trail off at λ > 30 μm. Additionally, we provide a relation between observed L X and pure AGN IR output for high-z AGN, allowing future studies to estimate AGN IR contribution using only observed X-ray flux density estimates.