BASS - XLIII. Optical, UV, and X-ray emission properties of unobscured Swift/BAT active galactic nuclei

Creators: Gupta, Kriti K.^{1, 2, 3}; Ricci, Claudio^{1, 4}; Temple, Matthew J.¹; Tortosa, Alessia⁵; Koss, Michael J.^{6, 7}; Assef, Roberto J.¹; Bauer, Franz E.^{8, 9}; Mushotzy, Richard¹⁰; Ricci, Federica^{5, 11}; Ueda, Yoshihiro¹²; Rojas, Alejandra F.^{1, 13}; Trakhtenbrot, Benny¹⁴; Chang, Chin-Shin¹⁵; Oh, Kyuseok¹⁶; Li, Ruancun^{4, 17}; Kawamuro, Taiki¹⁸; Diaz, Yaherlyn¹; Powell, Meredith C.¹⁹; Stern, Daniel²⁰; Megan Urry, C.²¹; Harrison, Fiona A.²²; Cenko, Brad²³

1. Diego Portales University
2. University of Liège
3. Ghent University
4. Peking University
5. Astronomical Observatory of Rome
6. Eureka Scientific
7. Space Science Institute
8. Pontificia Universidad Católica de Chile
9. Millennium Institute of Astrophysics
10. University of Maryland, College Park
11. Roma Tre University
12. Kyoto University
13. University of Antofagasta
14. Tel Aviv University
15. Atacama Large Millimeter Submillimeter Array
16. Korea Astronomy and Space Science Institute
17. Osaka University
18. RIKEN
19. Stanford University
20. Jet Propulsion Lab
21. Yale University
22. California Institute of Technology
23. Goddard Space Flight Center

Abstract

We present one of the largest multiwavelength studies of simultaneous optical-to-X-ray spectral energy distributions (SEDs) of unobscured (N_H < 10²² cm⁻²) active galactic nuclei (AGN) in the local Universe. Using a representative sample of hard-X-ray-selected AGN from the 70-month Swift/BAT catalog, with optical/UV photometric data from Swift/UVOT and X-ray spectral data from Swift/XRT, we constructed broadband SEDs of 236 nearby AGN (0.001 < z < 0.3). We employed GALFIT to estimate host galaxy contamination in the optical/UV and determine the intrinsic AGN fluxes. We used an absorbed power law with a reflection component to model the X-ray spectra and a dust-reddened multi-temperature blackbody to fit the optical/UV SED. We calculated intrinsic luminosities at multiple wavelengths, total bolometric luminosities (L_bol), optical-to-X-ray spectral indices (α_ox), and multiple bolometric corrections (κ_λ) in the optical, UV, and X-rays. We used black hole masses obtained by reverberation mapping and the virial method to estimate Eddington ratios (λ_Edd) for all our AGN. We confirm the tight correlation (scatter = 0.45 dex) between UV (2500 Å) and X-ray (2 keV) luminosity for our sample. We observe a significant decrease in α_ox with L_bol and λ_Edd, suggesting that brighter sources emit more UV photons per X-rays. We report a second-order regression relation (scatter = 0.15 dex) between the 2–10 keV bolometric correction (κ_2 − 10) and α_ox, which is useful to compute L_bol in the absence of multiband SEDs. We also investigate the dependence of optical/UV bolometric corrections on the physical properties of AGN and obtain a significant increase in the UV bolometric corrections (κ_W2 and κ_M2) with L_bol and λ_Edd, unlike those in the optical (κ_V and κ_B), which are constant across five orders of L_bol and λ_Edd. We obtain significant dispersions (∼0.1–1 dex) in all bolometric corrections, and hence recommend using appropriate relations with observed quantities while including the reported scatter, instead of their median values.

Copyright and License

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

Acknowledgement

We would like to thank the anonymous referee for their useful suggestions that helped improve this manuscript. This work made use of data from the NASA/IPAC Infrared Science Archive and NASA/IPAC Extragalactic Database (NED), which are 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 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 also made use of photutils, an Astropy package for the detection and photometry of astronomical sources (Bradley et al. 2021). We acknowledge financial support from: a 2018 grant from the ESO-Government of Chile Joint Committee (KKG); the Belgian Federal Science Policy Office (BELSPO) in the framework of the PRODEX Programme of the European Space Agency (KKG); ANID CATA-BASAL project FB210003 (CR, RJA, FEB); ANID FONDECYT Regular grant #1230345 (CR), #1231718 (RJA), and #1200495 (FEB); NASA ADAP award 80NSSC19K0749 (MJK); ANID Millennium Science Initiative Program - ICN12_009 (FEB); ANID FONDECYT Postdoctorado grant #3220516 (MJT), #3210157 (AFR), and #3230310 (YD); the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program, grant agreement #950533 (BT); the Israel Science Foundation, grant #1849/19 (BT); the Korea Astronomy and Space Science Institute under the R&D program supervised by the Ministry of Science and ICT, Project #2024-1-831-01 (KO); the National Research Foundation of Korea, NRF-2020R1C1C1005462 (KO).

Funding

We acknowledge financial support from: a 2018 grant from the ESO-Government of Chile Joint Committee (KKG); the Belgian Federal Science Policy Office (BELSPO) in the framework of the PRODEX Programme of the European Space Agency (KKG); ANID CATA-BASAL project FB210003 (CR, RJA, FEB); ANID FONDECYT Regular grant #1230345 (CR), #1231718 (RJA), and #1200495 (FEB); NASA ADAP award 80NSSC19K0749 (MJK); ANID Millennium Science Initiative Program - ICN12_009 (FEB); ANID FONDECYT Postdoctorado grant #3220516 (MJT), #3210157 (AFR), and #3230310 (YD); the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program, grant agreement #950533 (BT); the Israel Science Foundation, grant #1849/19 (BT); the Korea Astronomy and Space Science Institute under the R&D program supervised by the Ministry of Science and ICT, Project #2024-1-831-01 (KO); the National Research Foundation of Korea, NRF-2020R1C1C1005462 (KO).

Data Availability

All the optical-to-X-ray SED fits generated in this work are available https://zenodo.org/records/13741974?preview = 1&token=eyJhbGciOiJIUzUxMiJ9.eyJpZCI6ImFkNGViZjM0LTQxZjUtNDhlMi1hYzBiLWZiZTkzNzllZDRjYSIsImRhdGEiOnt9LCJyYW5kb20iOiI5ZDZmZTVlODgzYjI4MjFkZTE0MDYyNTk0MWQzMmYzMSJ9.gE6rtXFXYJwlh7aPv0pqTpSkxvLTNr5Ptcq6FllAuF6JM2ye2akZgXjuF2-bWIK0Il9gziVNsHRN9JsYLLDg. Full versions of Tables A.1 to A.10 are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/691/A203.

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