2016/04/26 by Michael J. Koss, R. Assef, M. Baloković +20
Physics and Astronomy · #Accretion (finance) #Accretion disc #Active galactic nucleus #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Balmer series #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Population #Spectral line #Telescope #astro-ph.GA #astro-ph.HE
paper · pdf · doi:10.3847/0004-637x/825/2/85
Accepted to ApJ, 19 pages, 12 figures
arxiv created 2016/04/26 · openalex created_date 2016/06/24 · openalex publication_date 2016/07/06 · arxiv updated 2016/07/13 · openalex updated_date 2026/08/05
ABSTRACT We present a new metric that uses the spectral curvature (SC) above 10 keV to identify Compton-thick active galactic nuclei (AGNs) in low-quality Swift /Burst Alert Telescope (BAT) X-ray data. Using NuSTAR , we observe nine high SC-selected AGNs. We find that high-sensitivity spectra show that the majority are Compton-thick (78% or 7/9) and the remaining two are nearly Compton-thick ( N H ≃ (5–8) × 10 23 cm −2 ). We find that the SC BAT and SC NuSTAR measurements are consistent, suggesting that this technique can be applied to future telescopes. We tested the SC method on well-known Compton-thick AGNs and found that it is much more effective than broadband ratios (e.g., 100% using SC versus 20% using 8–24 keV/3–8 keV). Our results suggest that using the >10 keV emission may be the only way to identify this population since only two sources show Compton-thick levels of excess in the Balmer decrement corrected [O iii ] to observed X-ray emission ratio ( ) and WISE colors do not identify most of them as AGNs. Based on this small sample, we find that a higher fraction of these AGNs are in the final merger stage (<10 kpc) than typical BAT AGNs. Additionally, these nine obscured AGNs have, on average, ≈4× higher accretion rates than other BAT-detected AGNs ( compared to ). The robustness of SC at identifying Compton-thick AGNs implies that a higher fraction of nearby AGNs may be Compton-thick (≈22%) and the sum of black hole growth in Compton-thick AGNs (Eddington ratio times population percentage) is nearly as large as mildly obscured and unobscured AGNs.