Probing the Structure and Evolution of BASS Active Galactic Nuclei through Eddington Ratios

Abstract We constrain the intrinsic Eddington ratio ( λ Edd ) distribution function for local active galactic nuclei (AGN) in bins of low and high obscuration [ log ( N H / cm − 2 ) ≤ 22 and 22 < log ( N H / cm − 2 ) < 25 ], using the Swift Burst Alert Telescope 70 month/BASS DR2 survey. We in...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2022-11, Vol.939 (1), p.L13
Main Authors: Ananna, Tonima Tasnim, Urry, C. Megan, Ricci, Claudio, Natarajan, Priyamvada, Hickox, Ryan C., Trakhtenbrot, Benny, Treister, Ezequiel, Weigel, Anna K., Ueda, Yoshihiro, Koss, Michael J., Bauer, F. E., Temple, Matthew J., Baloković, Mislav, Mushotzky, Richard, Auge, Connor, Sanders, David B., Kakkad, Darshan, Sartori, Lia F., Marchesi, Stefano, Harrison, Fiona, Stern, Daniel, Oh, Kyuseok, Caglar, Turgay, Powell, Meredith C., Podjed, Stephanie A., Mejía-Restrepo, Julian E.
Format: Article
Language:English
Subjects:
Accretion
Active galactic nuclei
Astronomical models
Astronomy data modeling
Distribution functions
Evolution
Luminosity function
Occultation
Ratios
Supermassive black holes
Toruses
X-ray active galactic nuclei
X-ray surveys
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Summary:Abstract We constrain the intrinsic Eddington ratio ( λ Edd ) distribution function for local active galactic nuclei (AGN) in bins of low and high obscuration [ log ( N H / cm − 2 ) ≤ 22 and 22 < log ( N H / cm − 2 ) < 25 ], using the Swift Burst Alert Telescope 70 month/BASS DR2 survey. We interpret the fraction of obscured AGN in terms of circumnuclear geometry and temporal evolution. Specifically, at low Eddington ratios ( log λ Edd < −2), obscured AGN outnumber unobscured ones by a factor of ∼4, reflecting the covering factor of the circumnuclear material (0.8, or a torus opening angle of ∼34°). At high Eddington ratios ( log λ Edd > −1), the trend is reversed, with 22 , which we suggest is mainly due to the small fraction of time spent in a highly obscured state. Considering the Eddington ratio distribution function of narrow-line and broad-line AGN from our prior work, we see a qualitatively similar picture. To disentangle temporal and geometric effects at high λ Edd , we explore plausible clearing scenarios such that the time-weighted covering factors agree with the observed population ratio. We find that the low fraction of obscured AGN at high λ Edd is primarily due to the fact that the covering factor drops very rapidly, with more than half the time spent with
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/ac9979