COMPTON-THICK ACCRETION IN THE LOCAL UNIVERSE

By C. Ricci, Y. Ueda, M. Koss, B. Trakhtenbrot, F. E. Bauer, Poshak Gandhi. 2015

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Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes and to play an important role in shaping the observed spectrum of the cosmic X-ray background. Hard X-ray (E > 10 keV) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of the best ways to detect and identify Compton-thick (CT, log N H ≥ 24 ?> ) active galactic nuclei (AGNs). In this letter we present the first results of the largest broadband (0.3–150 keV) X-ray spectral study of hard X-ray selected AGNs to date, focusing on the properties of heavily obscured sources. Our sample includes the 834 AGNs (728 non-blazar, average redshift z ≃ 0.055) reported in the 70-month catalog of the all-sky hard X-ray Swift/Burst Alert Monitor survey. We find 55 CT AGNs, which represent 7.6 − 2.1 + 1.1 % ?> of our non-blazar sample. Of these, 26 are reported as candidate CT AGNs for the first time. We correct for selection bias and derive the intrinsic column density distribution of AGNs in the local universe in two different luminosity ranges. We find a significant decrease in the fraction of obscured Compton-thin AGNs for increasing luminosity, from 46 ± 3% (for log L 14 − 195 ?> = 40–43.7) to 39 ± 3% (for log L 14 − 195 ?> = 43.7–46). A similar trend is also found for CT AGNs. The intrinsic fraction of CT AGNs with log N H ?> = 24–25 normalized to unity in the log N H ?> = 20–25 range is 27 ± 4%, and is consistent with the observed value obtained for AGNs located within 20 Mpc.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/0767d6f4caf0b69a38bcdc74c6c5aa94a39e4417

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Citations in the corpus

The 105-Month Swift-BAT All-sky Hard X-Ray Survey (2018, background): “…X-ray energy band, a hard X-ray all-sky survey (> 10 keV) provides an important way of studying astrophysical objects since such energetic hard X-ray photons can pass through large columns of gas and dust detecting even Compton-thick sources (NH > 1024cm−2, Ricci et al. 2015; Koss et al. 2016).”
New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei (2018, background): “In particular, Compton-thick (CT; NH > 1024 cm−2) AGN represent 20–50 % of the local AGN population (e.g., Ricci et al. 2015, Akylas et al. 2016, Koss et al. 2016), and it is widely believed that our line of sight crosses their tori in most cases (Ricci et al. 2017b).”
The bolometric quasar luminosity function at z = 0–7 (2020, methodology): “…and the CTK quasar fraction from this model with observations (Ueda et al. 2003; Burlon et al. 2011; Brightman & Ueda 2012; Merloni et al. 2014; Aird et al. 2015a; Buchner et al. 2015; Ricci et al. 2015; Del Moro et al. 2016; Georgakakis et al. 2017; Masini et al. 2018; Lanzuisi et al. 2018).”
BAT AGN Spectroscopic Survey. V. X-Ray Properties of the Swift/BAT 70-month AGN Catalog (2017, background): “The main properties of the CT AGN from our sample have been reported in a recently published paper (Ricci et al. 2015), while the spectral parameters obtained are listed in TableC7.”
The dust covering factor in active galactic nuclei (2016, background): “In the most complete study of local AGNs, Ricci et al. (2015) reconstructed the intrinsic column density (NH) in two luminosity bins and found that the intrinsic fraction of both Compton-thin and Compton-thick objects decreases with LAGN.”
The quest for dual and binary supermassive black holes: A multi-messenger view (2019, methodology): “In this regard, the fraction of dual AGN has been estimated by Koss et al. (2012) in a sample of local (z < 0.05), moderate-luminosity AGN selected from the all-sky hard-X ray Swift/BAT survey.”
BAT AGN Spectroscopic Survey. I. Spectral Measurements, Derived Quantities, and AGN Demographics (2017, methodology): “Full details of the X-ray analysis and fitting measurements are provided in separate publications (Ricci et al. 2015, Ricci et al., submitted.).”