Towards a complete census of luminous Compton-thick Active Galactic nuclei in the local Universe

Abstract

X-ray surveys provide the most efficient means for the detection of active galactic nuclei (AGNs). However, they do face difficulties in detecting the most heavily obscured Compton-thick AGNs. The BAT detector on board the Gehrels/Swift mission, operating in the very hard 14–195 keV band, has provided the largest samples of Compton-thick AGN in the Local Universe. However, even these flux-limited samples may miss the most obscured sources among the Compton-thick AGN population. A robust way to find these local sources is to systematically study volume-limited AGN samples detected in the IR or the optical part of the spectrum. Here, we utilise a local sample (< 100 Mpc) of mid-IR-selected AGNs, unbiased against obscuration, to determine the fraction of Compton-thick sources in the Local Universe. When available, we acquired X-ray spectral information for the sources in our sample from previously published studies. In addition, to maximise the X-ray spectral information for the sources in our sample, we analysed eleven unexplored XMM-Newton and NuSTAR observations, for the first time. In this way, we identified four new Compton-thick sources. Our results reveal an increased fraction of Compton-thick AGNs among the sources that have not been detected by BAT of 44%. Overall, we have estimated a 25–30% share of Compton-thick sources in the Local Universe among mid-IR-selected AGNs. We find no evidence for any evolution of the AGN Compton-thick fraction with luminosity.

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ORCID for P. Gandhi: orcid.org/0000-0003-3105-2615

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