THE 60 MONTH ALL-SKY BURST ALERT TELESCOPE SURVEY OF ACTIVE GALACTIC NUCLEUS AND THE ANISOTROPY OF NEARBY AGNs

Ajello, M.; Alexander, D. M.; Greiner, J.; Madejski, G. M.; Gehrels, N.; Burlon, D.

doi:10.1088/0004-637x/749/1/21

Cited by 109 publications

(163 citation statements)

References 66 publications

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“…It is now interesting to compare the results obtained here with those reported in Burlon et al (2011) or in the recent updated BAT all-sky catalogue published by Ajello et al (2012). Given the different selection band (IR and hard X-rays respectively) we can compare the two surveys only by assuming an average hard X-ray-to-IR flux ratio typical for AGN.…”

Section: Comparison With Other Samplesmentioning

confidence: 73%

“…For comparison, the efficiency in finding Compton-thick AGN using other X-rayto-mid-infrared diagnostic ratio (e.g. L X /L 6 μm , as recently proposed by Georgantopoulos et al 2011) is 50% and in a hard X-ray survey, like that presented in Burlon et al (2011) or in the recently published all-sky sample of AGN detected by BAT in 60 months of exposure (Ajello et al 2012), is about 5−6%.…”

Section: Efficiency and Completeness Of The Methodsmentioning

confidence: 90%

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A new technique to efficiently select Compton-thick AGN

Severgnini

Caccianiga

Ceca

2012

A&A

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Aims. We present a new efficient diagnostic method, based on mid-infrared and X-ray data, to select local (z < 0.1) Compton-thick AGN with the aim of estimating their surface and space density. Methods. We define a region in the X-ray-to-mid-IR [F(2−12 keV)/F 25 ν 25 ] vs. X-ray color (HR) plane associated to Compton-thick AGN, i.e. [F(2−12 keV)/F 25 ν 25 ] < 0.02 and HR > −0.2. On the basis of this selection method we build up a sample of 43 Comptonthick AGN candidates using data from IRAS Point Source and 2XMM-Newton catalogues. In order to test the efficiency of the proposed method in selecting Compton-thick AGN we use the results of the X-ray spectral analysis performed on all the sources of our sample (presented in a parallel work). After taking into account the different selection effects, we have estimated the number of Compton-thick in the local Universe and their density down to the IRAS flux limit of F 25 = 0.5 Jy. Results. We find that the diagnostic plot proposed here is an efficient method to select Compton-thick AGN in the nearby Universe since ∼84% of the sources populating the proposed Compton-thick region are actually Compton-thick AGN. Twenty percent are newly-discovered Compton-thick AGN. We then estimate the surface density of Compton-thick AGN down to the IRAS PSC catalogue flux limit (F 25 = 0.5 Jy) that turns out to be ρ CT ∼ 3 × 10 −3 src deg −2 . After estimating an equivalent IR-to-hard-X-ray limiting flux, we compare our result with those found with Swift-BAT. We find that the surface density derived here is a factor 4 above the density computed in the hard X-ray surveys. This difference is ascribed, at least in part, to a significant contribution (∼60−90%) of the star-forming activity to the total 25 μm emission for the sources in our sample. By considering only the 25 μm AGN emission, we estimate a surface density of Compton-thick AGN which is consistent with the results found by hard X-ray surveys. Finally, we estimated the co-moving space density of Compton-thick AGN with intrinsic L X > 10 43 erg s −1 (0.004 < z < 0.06): Φ C−thick ∼ (3.5 +4.5 −0.5 ) × 10 −6 Mpc −3 . The prediction for Compton-thick AGN based on the synthesis model of X-ray background in Gilli et al. (2007) is consistent with this value.

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Section: Comparison With Other Samplesmentioning

confidence: 73%

Section: Efficiency and Completeness Of The Methodsmentioning

confidence: 90%

A new technique to efficiently select Compton-thick AGN

Severgnini

Caccianiga

Ceca

2012

A&A

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“…Based on this luminosity function we derive a Comptonthick emissivity (luminosity density) of 7.7 × 10 37 erg s −1 Mpc −3 in the 20-40keV band. As the total AGN emissivity is 4.5 × 10 38 erg s −1 Mpc −3 , as derived from the total AGN luminosity function (Ajello et al 2012), the Compton-thick contribution to the total AGN emissivity is about 17%. Compton thick AGN luminosity function (this work) NuSTAR AGN luminosity function of Aird et al 2015b Parametric best fit model Compton thin AGN luminosity function of Ajello et al 2012 Fig.…”

Section: Luminosity Functionmentioning

confidence: 82%

“…Compton-thick AGN luminosity function in the 20-40 keV band derived from our sample; the binned luminosity function is denoted with red points and the parametric with the red line. The magenta dash-dotted line denotes the Compton-thin AGN luminosity function derived by Ajello et al (2012). The green points show the NuSTAR AGN luminosity function derived by Aird et al (2015b).…”

Section: Luminosity Functionmentioning

confidence: 99%

Compton-thick AGN in the 70-monthSwift-BAT All-Sky Hard X-ray Survey: A Bayesian approach

Akylas

Georgantopoulos

Ranalli

et al. 2016

A&A

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The 70-month Swift/BAT catalogue provides a sensitive view of the extragalactic X-ray sky at hard energies (>10 keV) containing about 800 active galactic nuclei (AGN). We explore its content in heavily obscured, Compton-thick AGN by combining the BAT (14-195 keV) with the lower energy XRT (0.3-10 keV) data. We apply a Bayesian methodology using Markov chains to estimate the exact probability distribution of the column density for each source. We find 53 possible Compton-thick sources (probability range 3 -100%) translating to a ∼7% fraction of the AGN in our sample. We derive the first parametric luminosity function of Compton-thick AGN. The unabsorbed luminosity function can be represented by a double power law with a break at L ∼ 2 × 10 42 ergs s −1 in the 20-40 keV band. The Compton-thick AGN contribute ∼17% of the total AGN emissivity. We derive an accurate Compton-thick number count distribution taking into account the exact probability of a source being Compton-thick and the flux uncertainties. This number count distribution is critical for the calibration of the X-ray background synthesis models, i.e. for constraining the intrinsic fraction of Compton-thick AGN. We find that the number counts distribution in the 14-195 keV band agrees well with our models which adopt a low intrinsic fraction of Compton-thick AGN (∼ 12%) among the total AGN population and a reflected emission of ∼ 5%. In the extreme case of zero reflection, the number counts can be modelled with a fraction of at most 30% Compton-thick AGN of the total AGN population and no reflection. Moreover, we compare our X-ray background synthesis models with the number counts in the softer 2-10 keV band. This band is more sensitive to the reflected component and thus helps us to break the degeneracy between the fraction of Compton-thick AGN and the reflection emission. The number counts in the 2-10 keV band are well above the models which assume a 30% Compton-thick AGN fraction and zero reflection, while they are in better agreement with models assuming 12% Compton-thick fraction and 5% reflection. The only viable alternative for models invoking a high number of Compton-thick AGN is to assume evolution in their number with redshift. For example, in the zero reflection model the intrinsic fraction of Compton-thick AGN should rise from 30% at redshift z∼ 0 to about 50% at a redshift of z=1.1.

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“…It is believed today that there is a significant fraction of obscured active galactic nuclei (AGN) that still remain unidentified at high-energy spectral-bands even in the current deepest surveys (the strongest evidence coming from X-ray studies, e.g., Comastri et al 2001;Ueda et al 2003;Gilli 2004;Worsley et al 2004Worsley et al , 2005Treister & Urry 2005;Martínez-Sansigre et al 2005;Draper & Ballantyne 2009;Burlon et al 2011;Ajello et al 2012;Moretti et al 2012). With an incomplete demography of actively accreting super-massive black holes, current galaxy evolution models accounting for AGN feedback (e.g., Granato et al 2004;Springel et al 2005;Croton et al 2006;Hopkins et al 2006;Bower et al 2006;Somerville et al 2008) probably remain poorly constrained.…”

Section: Introductionmentioning

confidence: 99%

The dependency of AGN infrared colour-selection on source luminosity and obscuration

Messias

Afonso

Salvato

et al. 2014

A&A

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Aims. This work addresses the AGN IR-selection dependency on intrinsic source luminosity and obscuration, in order to identify and characterise biases that could affect conclusions in studies. Methods. We study IR-selected AGN in the Chandra Deep Field South (CDFS) survey and in the Cosmological Survey (COSMOS). The AGN sample is divided into low and high X-ray luminosity classes and into unobscured (type-1) and obscured (type-2) classes by means of X-ray and optical spectroscopy data. Specifically in the X-ray regime, we adopt the intrinsic luminosity taking the estimated column density (N H ) into account. We also take the opportunity to highlight important differences resulting from adopting different methods of assessing AGN obscuration. Results. In agreement with previous studies, we also find that AGN IR-selection efficiency shows a decrease with decreasing source AGN X-ray luminosity. For the intermediate-luminosity AGN population (43.3 < ∼ log(L X [erg s −1 ]) < ∼ 44), the efficiency also worsens with increasing obscuration (N H ). The same sample also shows an evolution with cosmic time of the obscured fraction at the highest X-ray luminosities, independently of the adopted type-1/type-2 classification method. Conclusions. We confirm that AGN IR-selection is genuinely biased towards unobscured AGNe, but only at intermediate luminosities.At the highest luminosities, where AGN IR-selection is more efficient, there is no obscuration bias. We show that type-1 AGNe are intrinsically more luminous than type-2 AGNe only at z < ∼ 1.6, thus resulting in more type-1 AGN being selected when the IR survey is shallower. Based on this and other studies, we conclude that deep hard-X-ray coverages, high-resolution IR imaging, or a combination of IR and radio data are required to recover the lower luminosity obscured AGN population. In addition, wide IR surveys are needed to recover the rare powerful, obscured AGN population. Finally, when the James Webb Space Telescope comes online, the broad-band filters 2.0 µm, 4.4 µm, 7.7 µm, and 18 µm will be essential for disentangling AGN from non-AGN dominated SEDs at depths where spectroscopy becomes impractical.

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THE 60 MONTH ALL-SKY BURST ALERT TELESCOPE SURVEY OF ACTIVE GALACTIC NUCLEUS AND THE ANISOTROPY OF NEARBY AGNs

Cited by 109 publications

References 66 publications

A new technique to efficiently select Compton-thick AGN

A new technique to efficiently select Compton-thick AGN

Compton-thick AGN in the 70-monthSwift-BAT All-Sky Hard X-ray Survey: A Bayesian approach

The dependency of AGN infrared colour-selection on source luminosity and obscuration

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