THREE-YEAR SWIFT–BAT SURVEY OF ACTIVE GALACTIC NUCLEI: RECONCILING THEORY AND OBSERVATIONS?

By D. Burlon, M. P. I. Garching, M. Ajello, Menlo Park Kipac, J. Greiner, A. Comastri, Tech. U. Universe Muenchen, A. Merloni, N. Gehrels, G. Nasa. 2010

225 citations recorded by the source corpus.

It is well accepted that unabsorbed as well as absorbed active galactic nuclei (AGNs) are needed to explain the nature and shape of the Cosmic X-ray background (CXB), even if the fraction of highly absorbed objects (dubbed Compton-thick sources) still substantially escapes detection. We derive and analyze the absorption distribution using a complete sample of AGNs detected by Swift–BAT in the first three years of the survey. The fraction of Compton-thick AGNs represents only 4.6% of the total AGN population detected by Swift–BAT. However, we show that once corrected for the bias against the detection of very absorbed sources the real intrinsic fraction of Compton-thick AGNs is 20+9−6%. We proved for the first time (also in the Burst Alert Telescope (BAT) band) that the anti-correlation of the fraction of absorbed AGNs and luminosity is tightly connected to the different behavior of the X-ray luminosity functions (XLFs) of absorbed and unabsorbed AGNs. This points toward a difference between the two subsamples of objects with absorbed AGNs being, on average, intrinsically less luminous than unobscured ones. Moreover, the XLFs show that the fraction of obscured AGNs might also decrease at very low luminosity. This can be successfully interpreted in the framework of a disk cloud outflow scenario as the disappearance of the obscuring region below a critical luminosity. Our results are discussed in the framework of population synthesis models and the origin of the CXB.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/81b070cb5f0174e7d369405ec826bff5c6930514

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Citations in the corpus

• Stellar and Quasar Feedback in Concert: Effects on AGN Accretion, Obscuration, and Outflows (2015, unknown): “Quantitatively, we find a broad column density distribution from ∼ 1022− 1026 cm−2, in reasonable agreement with observations (e.g. Malizia et al. 2009; Treister et al. 2009; Risaliti et al. 1999; Burlon et al. 2011, and references therein).”
• The incidence of obscuration in active galactic nuclei (2013, background): “…fraction of absorbed AGN, defined in different and often independent ways, appears to be lower at higher nuclear luminosities (Lawrence & Elvis 1982; Steffen et al. 2003; Ueda et al. 2003; Simpson 2005; Hasinger 2008; Bongiorno et al. 2010; Brusa et al. 2010; Burlon et al. 2011; Assef et al. 2013).”
• GeV OBSERVATIONS OF STAR-FORMING GALAXIES WITH THE FERMI LARGE AREA TELESCOPE (2012, background): “Hard X-ray emission is a strong and relatively unbiased identifier of AGN activity (Burlon et al. 2011), while soft X-ray emission from AGN is more often obscured by intervening circumnuclear and ISM material.”
• ON THE UNIFICATION OF ACTIVE GALACTIC NUCLEI (2012, methodology): “…Compton thick AGNs (X-ray obscuring column NH & 1024 cm−2) was determined to be as high as 50% in a pre-selected sample of Seyfert 2 (Risaliti et al. 1999; Guainazzi et al. 2005) but only ∼ 20% in complete X-ray samples without spectroscopic pre-selection (Malizia et al. 2009; Burlon et al. 2011).”
• COMPTON-THICK ACCRETION IN THE LOCAL UNIVERSE (2015, result): “This value is larger than that predicted at low z by Aird et al. (2015), but is in very good agreement with that inferred by Burlon et al. (2011) (20 %6 9 - + ) using a smaller sample of ∼200 Swift/BATselected AGNs.”
• TOWARD THE STANDARD POPULATION SYNTHESIS MODEL OF THE X-RAY BACKGROUND: EVOLUTION OF X-RAY LUMINOSITY AND ABSORPTION FUNCTIONS OF ACTIVE GALACTIC NUCLEI INCLUDING COMPTON-THICK POPULATIONS (2014, methodology): “Note that using theSwift/BAT 3-year survey, Burlon et al. (2011) report a slightly smaller CTK fraction of 20+9−6% than the above value, though within the errors, because they do not include heavily CTK AGNs with log NH > 25.”
• OBSCURATION-DEPENDENT EVOLUTION OF ACTIVE GALACTIC NUCLEI (2015, methodology): “The blue data point at z < 0.1 was taken from the Swift/BAT analysis of Burlon et al. (2011), where a considerably lower Compton-thick fraction was found, in disagreement to our findings.”
• The bolometric quasar luminosity function at z = 0–7 (2020, methodology): “…3, we compare the predictions on the absorbed quasar fraction 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;…”
• What drives the growth of black holes (2011, background): “Sensitive radio, mid-IR spectroscopy, and X-ray observations (particularly at > 10 keV; e.g., Sazonov et al. 2007; Winter et al. 2009; Burlon et al. 2011) further extend our understanding and census of nearby AGN activity, providing the identification of AGNs even in the presence of significant…”
• Cosmic X-ray surveys of distant active galaxies (2015, background): “…contributed substantially, has been in clarifying the long-suspected (e.g., Lawrence and Elvis 1982; Lawrence 1991) luminosity dependence of the fraction of obscured AGNs (e.g., Treister and Urry 2006; Hasinger 2008; Burlon et al 2011; Brightman et al 2014; Merloni et al 2014; Ueda et al 2014).”
• New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei (2018, background): “AGN population studies in the X-ray band suggest that the fraction of obscured AGN drops as a function of luminosity (e.g., Sazonov & Revnivtsev 2004, Hasinger 2008, Burlon et al. 2011, Vasudevan et al. 2013).”
• The nature of the Compton-thick X-ray reprocessor in NGC 4945 (2012, background): “The Burst Alert telescope (BAT, Barthelmy et al. 2005) aboard the Swift satellite (Geherls et al. 2004) has been conducting an all-sky hard X-ray survey in the 14–195 keV band since 2004, November (e.g. see Tueller et al. 2010; Burlon et al. 2011).”
• BAT AGN Spectroscopic Survey. V. X-Ray Properties of the Swift/BAT 70-month AGN Catalog (2017, background): “…of obscured and unobscured AGN (e.g., Della Ceca et al. 2008; Burlon et al. 2011; Aird et al. 2015), and is consistent with the observed decrease of the fraction of obscured sources with increasing luminosity (e.g., Ueda et al. 2003; Treister & Urry 2006; Burlon et al. 2011; Ueda et al. 2014).”
• Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured (2017, background): “%) compared to local hard X-ray selected AGN (27±4%, Ricci et al. 2015; see also Burlon et al. 2011), which are mostly found in non-merging systems4.”
• The dust covering factor in active galactic nuclei (2016, background): “The decrease of the covering factor of the torus with increasing luminosity is systematically found in X-ray surveys (e.g. Ueda et al. 2003; Beckmann et al. 2009; Burlon et al. 2011; Ricci et al. 2013; Merloni et al. 2014; Ueda et al. 2014; Buchner et al. 2015).”