Abstract

We analyze Spitzer spectra of 140 active galactic nuclei (AGN) detected in the hard X-rays (14-195 keV) by the Burst Alert Telescope on board Swift. This sample allows us to probe several orders of magnitude in black hole masses (106-109 M ), Eddington ratios (10−3-1), X-ray luminosities (1042-1045 erg s−1), and X-ray column densities (1020-1024 cm−2). The AGN emission is expected to be the dominant source of ionizing photons with energies ≳50 eV, and therefore, high-ionization mid-infrared (MIR) emission lines such as [Ne v] 14.32, 24.32 μm and [O iv] 25.89 μm are predicted to be good proxies of AGN activity, and robust against obscuration effects. We find high detection rates (≳85%-90%) for the MIR coronal emission lines in our AGN sample. The luminosities of these lines are correlated with the 14-150 keV luminosity (with a typical scatter of σ ∼0.4-0.5 dex), strongly indicating that the MIR coronal line (CL) emission is driven by AGN activity. CLs are also tightly correlated to the bolometric luminosity (σ ∼0.2-0.3 dex), calculated from careful analysis of the spectral energy distribution. We find that the relationship between the CL strengths and L 14-150 keV is independent of black hole mass, AGN luminosity, and Eddington ratio, and mostly not affected by high X-ray column densities. This confirms that the MIR CLs can be used as unbiased tracers of the AGN power for X-ray luminosities in the 1042-1045 erg s−1 range.

Original languageEnglish
Article number257
JournalAstrophysical Journal
Volume976
Issue number2
DOIs
StatePublished - 1 Dec 2024

Funding

FundersFunder number
National Aeronautics and Space Administration
Consejería de Economía, Industria, Comercio y Conocimiento
BEL
Instituto de Astrofísica de Canarias
Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias
Spanish Ministry of Science, Innovation and Universities MCIU
Fundación Jesús Serra
Belgian Federal Science Policy Office
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Oak Ridge Associated Universities
Agencia Canaria de Investigación, Innovación y Sociedad de la Información
European Space Agency3210157
Fondecyt RegularFB210003, 1230345
Agencia Nacional de Investigación y Desarrollo1241005, 1200495, CATA-BASAL FB210003, AIM23-0001, ICN12_009
Conselho Nacional de Desenvolvimento Científico e Tecnológico311223/2020-6, 400352/2016-8, 304927/2017-1
Fondo Nacional de Desarrollo Científico y Tecnológico3230310, 3220516
European Regional Development FundPID2019-107427GB-C32, ProID2021010079
Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul19/1750-2, 16/2551-0000251-7

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