Search

We present a comprehensive X-ray analysis and spectral energy distribution (SED) fitting of WISEA J171419.96+602724.6, an extremely luminous type 2 quasar at z = 2.99. The source was suggested as a candidate Compton-thick (column density N _H > 1.5×10 ^24 cm ^−2 ) quasar by a short XMM-Newton observation in 2011. We recently observed the source with deep NuSTAR and XMM-Newton exposures in 2021 and found that the source has a lower obscuration of N _H ∼ 5×10 ^22 cm ^−2 with an about four times lower flux. The two epochs of observations suggested that the source was significantly variable in X-ray obscuration, flux, and intrinsic luminosity at 2 σ –3 σ in less than 2.5 yr (in the source rest frame). We performed SED fitting of this source using Code Investigating GALaxy Emission thanks to its great availability of multiwavelength data (from hard X-rays to radio). The source is very luminous, with a bolometric luminosity of L _BOL ∼ 2.5 × 10 ^47 erg s ^−1 . Its host galaxy has a huge star formation rate (SFR) of ∼1280 M _☉ yr ^−1 and a huge stellar mass of ∼1.1 × 10 ^12 M _☉ . The correlation between the SFR and stellar mass of this source is consistent with what was measured in the high- z quasars. It is also consistent with what was measured in the main-sequence star-forming galaxies, suggesting that the presence of the active nucleus in our target does not enhance or suppress the SFR of its host galaxy. The source is an infrared hyperluminous, obscured galaxy with a significant amount of hot dust in its torus and shares many similar properties with hot, dust-obscured galaxies.

In this study, we use the Swift/BAT AGN sample, which has received extensive multiwavelength follow-up analysis as a result of the BAT AGN Spectroscopic Survey, to develop a diagnostic for nuclear obscuration by examining the relationship between the line-of-sight column densities ( N _H ), the 2–10 keV to 12 μ m luminosity ratio, and WISE mid-infrared colors. We demonstrate that heavily obscured AGNs tend to exhibit both preferentially “redder” mid-infrared colors and lower values of L _X,Obs. / L _12 _μ _m than less obscured AGNs, and we derive expressions relating N _H to the L _X,Obs. / L _12 _μ _m and L _22 _μ _m / L _4.6 _μ _m luminosity ratios, as well as develop diagnostic criteria using these ratios. Our diagnostic regions yield samples that are ≳80% complete and ≳60% pure for AGNs with log( N _H /cm ^−2 ) ≥ 24, as well as ≳85% pure for AGNs with $\mathrm{log}({N}_{{\rm{H}}}/{\mathrm{cm}}^{-2})\gtrsim 23.5$ . We find that these diagnostics cannot be used to differentiate between optically star-forming galaxies and active galaxies. Further, mid-IR contributions from host galaxies that dominate the observed 12 μ m emission can lead to larger apparent X-ray deficits and redder mid-IR colors than the AGNs would intrinsically exhibit, though this effect helps to better separate less and more obscured AGNs. Finally, we test our diagnostics on two catalogs of AGNs and infrared galaxies, including the XMM-Newton XXL-N field, and we identify several known Compton-thick AGNs, as well as a handful of candidate heavily obscured AGNs based upon our proposed obscuration diagnostics.