A Large Population of Luminous Active Galactic Nuclei Lacking X-Ray Detections: Evidence for Heavy Obscuration?

Abstract We present a large sample of infrared-luminous candidate active galactic nuclei (AGNs) that lack X-ray detections in Chandra, XMM-Newton, and NuSTAR fields. selected all optically detected SDSS sources with redshift measurements, combined additional broadband photometry from WISE, UKIDSS, 2MASS, GALEX, modeled the spectral energy distributions (SEDs) our sources. parameterize nuclear obscuration SEDs uncover thousands powerful obscured AGNs counterparts, many which are identified as AGN candidates based on straightforward WISE photometric criteria. Using observed luminosity correlation between rest-frame 2–10 keV ( ${L}_{{\rm{X}}}$?> ) $6\,\mu {\rm{m}}$?> ${L}_{\mathrm{MIR}}$?> ), we estimate intrinsic luminosities combine these data flux limits catalogs to determine lower obscuration. ratio intrinsic-to-observed ${R}_{{L}_{{\rm{X}}}}$?> find significant fraction column densities approaching ${N}_{{\rm{H}}}\gt {10}^{24}$?> cm –2 , suggesting multiwavelength observations necessary account for population heavily AGNs. simulate underlying ${N}_{{\rm{H}}}$?> distribution non-detected through survival analysis, confirm presence activity via stacking. Our results point considerable extremely undetected by current observatories.