The incidence of obscuration in active galactic nuclei

By A. Merloni, A. Bongiorno, M. Brusa, K. Iwasawa, V. Mainieri, B. Magnelli, Mara Salvato, S. Berta, N. Cappelluti, A. Comastri and 15 more. 2013

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We study the incidence of nuclear obscuration on a complete sample of 1310 AGN selected on the basis of their rest-frame 2‐10 keV X-ray flux from the XM M-COSMOS survey, in the redshift range 0.3 < z < 3.5. We classify the AGN as obscured or un-obscured on the basis of either the optical spectral properties and the over all SED or the shape of the X-ray spectrum. The two classifications agree in about 70% of the ob jects, and the remaining 30% can be further subdivided into two distinct classes: at low l uminosities X-ray un-obscured AGN do not always show signs of broad lines or blue/UV continuum emission in their optical spectra, most likely due to galaxy dilution effects; a t high luminosities broad line AGN may have absorbed X-ray spectra, which hints at an increased incidence of small-scale (subparsec) dust-free obscuration. We confirm that the fraction of obscured AGN is a decreasing function of the intrinsic X-ray luminosity, while the incid ence of absorption shows significant evolution only for the most luminous AGN, which appear to be more commonly obscured at higher redshift. We find no significant difference between th e mean stellar masses and star formation rates of obscured and un-obscured AGN hosts. We conclude that the physical state of the medium responsible for obscuration in AGN is complex, and mainly determined by the radiation environment (nuclear luminosity) in a small region enclosed within the gravitational sphere of influence of the central black hole, but is la rgely insensitive to the wider scale galactic conditions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c89e194fe756b19c0a89a45bab400283695ae9a2

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In Astronomy and Astrophysics

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Citations in the corpus

• The bolometric quasar luminosity function at z = 0–7 (2020, methodology): “…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; Georgakakis et al. 2017; Masini et al. 2018;…”
• Cosmic X-ray surveys of distant active galaxies (2015, background): “…complex issue requiring much further work, and understanding such relations thoroughly will elucidate the structure and kinematics of the obscuring material (e.g., Mainieri et al 2007; Trouille et al 2009; Lawrence and Elvis 2010; Luo et al 2010; Merloni et al 2014 and references therein).”
• COSMIC REIONIZATION AFTER PLANCK: COULD QUASARS DO IT ALL? (2015, unknown): “Using αuv = 0.61 as before, αox = 1.37 (Lusso et al. 2010), αx = 0.9, zx = 5, and RII = 2 (Merloni et al. 2014) we obtain J2 keV = 1.64× 10 −27 erg cm−2 s−1Hz−1 sr−1, i.e. a contribution of nearly 60% to the unresolved XRB.”
• The dust covering factor in active galactic nuclei (2016, background): “Further discussions on this and related issues can be found in Merloni et al. (2014) and Netzer (2015).”
• Revisiting the Unified Model of Active Galactic Nuclei (2015, methodology): “In the local Universe, such objects represent about 30% of all type-II objects (Panessa & Bassani 2002, Tran 2003, Shi et al. 2010, Brightman & Nandra 2011b, Marinucci et al. 2012, Merloni et al. 2014).”
• Active galactic nuclei: what’s in a name? (2017, result): “Overall there is also good agreement between the optical and X-ray signatures of absorption (e.g. Malizia et al. 2012; Merloni et al. 2014; Burtscher et al. 2016): the majority (>80–90”
• BAT AGN Spectroscopic Survey. I. Spectral Measurements, Derived Quantities, and AGN Demographics (2017, result): “For both the 14–195 keV and 2–10 keV luminosities we find a general increase in type 1 fraction with increasing luminosity, as has been found in past studies using broad Hβ (see e.g., Merloni et al. 2014, and references therein).”
• The cosmic evolution of massive black holes in the Horizon-AGN simulation (2016, background): “The obscured fraction varies as a function of redshift and luminosity, and it is estimated to be ∼80 per cent at Lbol ∼ 1043 erg s−1 and between ∼10 and 80 at Lbol ∼ 1045 erg s−1, depending on redshift, according to X-ray studies (e.g. La Franca et al. 2005; Merloni et al. 2014; Ueda et al. 2014).”
• X-shooter reveals powerful outflows in z ∼ 1.5 X-ray selected obscured quasi-stellar objects (2014, methodology): “…(LX, unobscured) and column densities are in the 0.5-10 keV rest frame range and they are obtained from proper spectral analysis if available (Mainieri et al. 2011) or from rest frame flux corrected from absorption as inferred from the HR (sources marked with †, following Merloni et al. 2014).”
• Faint AGNs at z > 4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe (2015, background): “44) shows that the fraction of obscured AGNs at high redshifts could be ∼ 50% (Hasinger (2008), Merloni et al. (2014)) although there is no tight correlation between X-ray absorption and the presence of broad emission lines since some X-ray absorbed AGNs show broad emission lines in their…”
• THE CHANDRA COSMOS LEGACY SURVEY: OPTICAL/IR IDENTIFICATIONS (2015, background): “The same trend has already been confirmed by XMM-COSMOS, on the basis of the optical classification of the sources, for both the whole survey (B10) and in different redshift bins (Merloni et al. 2014).”