Compton-Thick AGN in the NuSTAR era VI: The observed Compton-thick fraction in the Local Universe

TL;DR

This study analyzes NuSTAR and XMM-Newton data of local Compton-thick AGN candidates, confirming 5 new cases, and refines the observed fraction of such AGN in the nearby universe, emphasizing NuSTAR's role in accurate classification.

Contribution

It provides the first comprehensive analysis of local Compton-thick AGN using simultaneous NuSTAR and XMM-Newton data, confirming new cases and updating the fraction estimates.

Findings

Confirmed 5 new Compton-thick AGN, increasing known total to 32.

Observed Compton-thick AGN fraction is approximately 8% in the local universe.

NuSTAR data significantly improves the classification accuracy of obscured AGN.

Abstract

We present the analysis of simultaneous NuSTAR and XMM-Newton data of 8 Compton-thick (CT-) active galactic nuclei (AGN) candidates selected in the Swift-Burst Alert Telescope (BAT) 100 month survey. This work is part of an ongoing effort to find and characterize all CT-AGN in the local ($z\leq$0.05) Universe. We used two physically motivated models, MYTorus and borus02, to characterize the sources in the sample, finding 5 of them to be confirmed CT-AGN. These results represent an increase of $\sim19$% over the previous NuSTAR-confirmed, BAT-selected CT-AGN at $z\leq0.05$, bringing the total number to 32. This corresponds to an observed fraction of $\sim 8$\% of all AGN within this volume-limited sample, although it increases to $20\pm5$% when limiting the sample to $z\leq0.01$. Out of a sample of 48 CT-AGN candidates, selected using BAT and soft (0.3$-$10 keV) X-ray data, only 24 are confirmed as CT-AGN with the addition of the NuSTAR data. This highlights the importance of NuSTAR when classifying local obscured AGN. We also note that most of the sources in our full sample of 48 Seyfert 2 galaxies with NuSTAR data have significantly different line-of-sight and average torus column densities, favouring a patchy torus scenario.