The NuSTAR Local AGN N_H Distribution Survey (NuLANDS). I. Toward a Truly Representative Column Density Distribution in the Local Universe

Creators: Boorman, Peter G.^{1, 2, 3}; Gandhi, Poshak²; Buchner, Johannes^{4, 5, 6}; Stern, Daniel⁷; Ricci, Claudio^{8, 9}; Baloković, Mislav^{10, 11}; Asmus, Daniel^{2, 12}; Harrison, Fiona A.¹; Svoboda, Jiří³; Greenwell, Claire^{2, 13}; Koss, Michael J.¹⁴; Alexander, David M.¹³; Annuar, Adlyka^{13, 15}; Bauer, Franz E.^{5, 16, 17}; Brandt, William N.¹⁸; Brightman, Murray¹; Civano, Francesca¹⁹; Chen, Chien-Ting J.^{20, 21}; Farrah, Duncan²²; Forster, Karl¹; Grefenstette, Brian¹; Hönig, Sebastian F.²; Hill, Adam B.^{2, 23}; Kammoun, Elias^{24, 25}; Lansbury, George^{26, 27}; Lanz, Lauranne²⁸; LaMassa, Stephanie²⁹; Madsen, Kristin¹⁹; Marchesi, Stefano^{30, 31, 32}; Middleton, Matthew²; Mingo, Beatriz³³; Parker, Michael L.³⁴; Treister, Ezequiel⁵; Ueda, Yoshihiro³⁵; Urry, C. Megan^{10, 11}; Zappacosta, Luca³⁶

1. California Institute of Technology
2. University of Southampton
3. Czech Academy of Sciences
4. Max Planck Institute for Extraterrestrial Physics
5. Pontificia Universidad Católica de Chile
6. Excellence Cluster Universe
7. Jet Propulsion Lab
8. Diego Portales University
9. Peking University
10. Yale Center for Astronomy & Astrophysics, 219 Prospect Street, New Haven, CT 06511, USA
11. Yale University
12. Gymnasium Schwarzenbek, 21493 Schwarzenbek, Germany
13. Durham University
14. Eureka Scientific
15. National University of Malaysia
16. Millennium Institute of Astrophysics
17. Space Science Institute
18. Pennsylvania State University
19. Goddard Space Flight Center
20. Universities Space Research Association
21. Marshall Space Flight Center
22. University of Hawaii at Manoa
23. ComplyAdvantage, 2nd Floor, Fetter Yard, Fetter Lane, London, EC4A 1AD, UK
24. Roma Tre University
25. Arcetri Astrophysical Observatory
26. European Southern Observatory
27. University of Cambridge
28. College of New Jersey
29. Space Telescope Science Institute
30. University of Bologna
31. Clemson University
32. INAF—Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti, 93/3, 40129, Bologna, Italy
33. The Open University
34. Optibrium (United Kingdom)
35. Kyoto University
36. Astronomical Observatory of Rome

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Abstract

Hard X-ray-selected samples of active galactic nuclei (AGN) provide one of the cleanest views of supermassive black hole accretion but are biased against objects obscured by Compton-thick gas column densities of N_H > 10²⁴ cm⁻². To tackle this issue, we present the NuSTAR Local AGN N_H Distribution Survey (NuLANDS)—a legacy sample of 122 nearby (z < 0.044) AGN primarily selected to have warm infrared colors from IRAS between 25 and 60 μm. We show that optically classified Type 1 and 2 AGN in NuLANDS are indistinguishable in terms of optical [O iii] line flux and mid-to-far-infrared AGN continuum bolometric indicators, as expected from an isotropically selected AGN sample, while Type 2 AGN are deficient in terms of their observed hard X-ray flux. By testing many X-ray spectroscopic models, we show the measured line-of-sight column density varies on average by ∼1.4 orders of magnitude depending on the obscurer geometry. To circumvent such issues, we propagate the uncertainties per source into the parent column density distribution, finding a directly measured Compton-thick fraction of 35% ± 9%. By construction, our sample will miss sources affected by severe narrow-line reddening, and thus segregates sources dominated by small-scale nuclear obscuration from large-scale host-galaxy obscuration. This bias implies an even higher intrinsic obscured AGN fraction may be possible, although tests for additional biases arising from our infrared selection find no strong effects on the measured column density distribution. NuLANDS thus holds potential as an optimized sample for future follow-up with current and next-generation instruments aiming to study the local AGN population in an isotropic manner.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

The authors are very grateful to the anonymous referee for their careful reading of the manuscript as well as for providing useful and constructive comments that improved the paper. P.G.B. would also like to thank Alberto Masini, Abhijeet Borkar, Emily Moravec, Daniel Kynoch, Ryan Pfeifle, Ari Laor, Giorgio Matt, Núria Torres-Albà, Lea Marcotulli, and many others for useful discussions. This work relied heavily on the use of Sherpa and PyXspec, and P.G.B. would thus like to extend his thanks to the helpdesks of either team, especially Nicholas Lee for his help with the use of the Sherpa package.

P.G.B. acknowledges financial support from the STFC. P.G.B. additionally thanks the Royal Astronomical Society and Institute of Physics for bursaries awarded in part to support the project, as well as support from the UGC-UKIERI (University Grants Commission—UK-India Education and Research Initiative) Phase 3 Thematic Partnerships. P.G. (grant reference ST/R000506/1) thanks the STFC for its support. M.B. acknowledges support from the black hole Initiative at Harvard University, which is funded by a grant from the John Templeton Foundation. We acknowledge support from ANID-Chile through the Millennium Science Initiative Program ICN12_009 (F.E.B.), CATA-BASAL FB210003 (C.R., F.E.B., E.T.), and FONDECYT Regular grants 1200495 (F.E.B., E.T.) and 1230345 (C.R.). I.M.M. acknowledges support from the National Research Foundation of South Africa. J.S. acknowledges the Czech Science Foundation project No. 22-22643S. A.A. acknowledges financial support from Universiti Kebangsaan Malaysia through Geran Universiti Penyelidikan code GUP-2023-033. C.G. acknowledges financial support from the Science and Technology Facilities Council (STFC) through grant codes ST/T000244/1 and ST/X001075/1. M.K. acknowledges support from NASA through ADAP award 80NSSC22K1126. F.E.B. acknowledges support from ANID-Chile BASAL CATA FB210003, FONDECYT Regular 1241005, and Millennium Science Initiative AIM23-0001. D.M.A. thanks the Science Technology Facilities Council (STFC) for support from the Durham consolidated grant (grant ST/T000244/1).

This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for their support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).

This work made use of data from XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

This work made use of data supplied by the UK Swift Science Data Center at the University of Leicester.

This publication makes use of data products from WISE, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration.

This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory.

This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

This research has made use of NASA's Astrophysics Data System Bibliographic Services.

This research has made use of the simbad database, operated at CDS, Strasbourg, France.

Software References

This work made extensive use of the NumPy (S. van der Walt et al. 2011), Matplotlib (J. D. Hunter 2007), SciPy(P. Virtanen et al. 2020), pandas (W. McKinney 2010), Astropy (Astropy Collaboration et al. 2013) Python packages.

Facilities

NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, Swift, XMM-Newton, Suzaku, Chandra, IRAS, WISE.

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