The Compton-thick AGN population and the NH distribution of low-mass AGN in our cosmic backyard

Creators: Annuar, A.¹; Alexander, D. M.²; Gandhi, P.³; Lansbury, G. B.⁴; Rosli, M. N.¹; Stern, D.⁵; Asmus, D.⁶; Ballantyne, D. R.⁷; Baloković, M.⁸; Bauer, F. E.^{9, 10, 11}; Boorman, P. G.¹²; Brandt, W. N.¹³; Brightman, M.¹²; Chen, C. T. J.^{14, 15}; Del Moro, A.¹⁶; Farrah, D.¹⁷; Harrison, F. A.¹²; Koss, M. J.¹⁸; Lanz, L.¹⁹; Marchesi, S.^{20, 21, 22}; Mohanadas, P.¹; Nardini, E.²³; Ricci, C.^{24, 25}; Zappacosta, L.²⁶

1. National University of Malaysia
2. Durham University
3. University of Southampton
4. European Southern Observatory
5. Jet Propulsion Lab
6. Gymnasium Schwarzenbek, 21493 Schwarzenbek, Germany
7. Georgia Institute of Technology
8. Yale University
9. Pontificia Universidad Católica de Chile
10. Millennium Institute of Astrophysics
11. Space Science Institute
12. California Institute of Technology
13. Pennsylvania State University
14. Universities Space Research Association
15. Marshall Space Flight Center
16. German Aerospace Center
17. University of Hawaii at Manoa
18. Eureka Scientific
19. College of New Jersey
20. University of Bologna
21. Clemson University
22. INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti, 93/3, I-40129 Bologna, Italy
23. INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
24. Diego Portales University
25. Peking University
26. Astronomical Observatory of Rome

Abstract

We present a census of the Compton-thick (CT) active galactic nucleus (AGN) population and the column density (N_H⁠⁠) distribution of AGN in our cosmic backyard using a mid-infrared selected AGN sample within 15 Mpc. The column densities are measured from broad-band X-ray spectral analysis, mainly using data from Chandra and NuSTAR. Our sample probes AGN with intrinsic 2–10 keV luminosities of L₂₋₁₀,int = 10³⁷-10⁴³ erg s⁻¹, reaching a parameter space inaccessible to more distant samples. We directly measure a 32⁺³⁰₋₁₈ CT AGN fraction and obtain an N_H distribution that agrees with that inferred by the Swift-BAT survey. Restricting the sample to the largely unexplored domain of low-luminosity AGN with L₂₋₁₀,int ≤ 10⁴² erg s⁻¹⁠, we found a CT fraction of ⁠19⁺³⁰₋₁₄ per cent, consistent with those observed at higher luminosities. Comparing the host-galaxy properties between the two samples, we find consistent star formation rates, though the majority of our galaxy have lower stellar masses (by ≈ 0.3 dex). In contrast, the two samples have very different black hole mass (M_(BH)⁠⁠) distributions, with our sample having ≈ 1.5 dex lower mean mass (M_(BH)⁠ ~10⁶ M⊙⁠). Additionally, our sample contains a significantly higher number of LINERs and H ii-type nuclei. The Eddington ratio range probed by our sample, however, is the same as Swift-BAT, although the latter dominates at higher accretion rates, and our sample is more evenly distributed. The majority of our sample with λEdd ≥ 10⁻³ tend to be CT, while those with λEdd < 10⁻³ are mostly unobscured or mildly obscured.

Copyright and License

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

AA acknowledges financial support from Universiti Kebangsaan Malaysia’s Geran Universiti Penyelidikan grant code GUP-2023-033 and the Merdeka Award Grant for International Attachment 2021. DMA acknowledges the Science and Technology Facilities Council (STFC) for support through grant code ST/T000244/1. MNR acknowledges support from the MyBrainSc Scholarship programme under the Ministry of Higher Education Malaysia (MoHE). CR acknowledges support from Fondecyt Regular grant 1230345 and ANID BASAL project FB210003. DRB is supported in part by NASA award 80NSSC24K0212 and NSF grants AST-2307278 and AST-2407658.

Data Availability

This work made use of data from the NuSTAR mission. NuSTAR is a project led by the California Institute of Technology (Caltech), managed by the Jet Propulsion Laboratory (JPL), and funded by the National Aeronautics and Space Administration (NASA). We thank the NuSTAR Operations, Software and Calibrations teams for support with 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 Caltech (USA). The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory and data obtained from the Chandra Data Archive. This research has made use of software provided by the Chandra X-ray Center (CXC) in the application packages ciao. This work was also based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

This research made use of various Python packages. We also used data obtained through the High Energy Astrophysics Science Archive Research Center (HEASARC) Online Service, provided by the NASA/Goddard Space Flight Center. The data used in this paper are publicly available and can be accessed and downloaded from NASA’s HEASARC (https://heasarc.gsfc.nasa.gov/docs/archive.html); details of the X-ray observations, including their identification numbers, are provided in Table 2. Most of the data presented in this research were taken from GA09 or Goulding et al. (2010), while the remaining data sources are specified in the notes section of Table 1. In addition, we used the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

Facilities

Chandra, NuSTAR, Swift and XMM–Newton.

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