Extreme X-Ray Iron Lines in Active Galactic Nuclei

Levenson, N. A.; Krolik, Julian H.; Życki, P. T.; Heckman, Timothy M.; Weaver, K. A.; Awaki, Hisamitsu; Terashima, Yuichi

doi:10.1086/342092

Cited by 85 publications

(127 citation statements)

References 32 publications

(26 reference statements)

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“…Additionally, the EW of the Fe-Kα emission line was reported as -+ 3.20 1.74 0.98 keV. Such high EWs are extreme though not unheard of, as reported by Levenson et al (2002). Optical images of the source, as well as surrounding source redshifts, infer IC 3639 to be part of a triple merger system (e.g., Figure 1(a), upper left panel-IC 3639 is ∼1 5 away from its nearest galaxy neighbor to the northeast).…”

Section: The Targetsupporting

confidence: 53%

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IC 3639—A NEW BONA FIDE COMPTON-THICK AGN UNVEILED BY NuSTAR

Boorman

Gandhi

Alexander

et al. 2016

ApJ

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We analyse high-quality NuSTAR observations of the local (z = 0.011) Seyfert 2 active galactic nucleus (AGN) IC 3639, in conjunction with archival Suzaku and Chandra data. This provides the first broadband X-ray spectral analysis of the source, spanning nearly two decades in energy (0.5 -30 keV). Previous X-ray observations of the source below 10 keV indicated strong reflection/obscuration on the basis of a pronounced iron fluorescence line at 6.4 keV. The hard X-ray energy coverage of NuSTAR, together with self-consistent toroidal reprocessing models, enables direct broadband constraints on the obscuring column density of the source. We find the source to be heavily Compton-thick (CTK) with an obscuring column in excess of 3.6 × 10 24 cm −2 , unconstrained at the upper end. We further find an intrinsic 2 -10 keV luminosity of log 10 (L 2 -10 keV [erg s−1 ]) = 43.4 +0.6 −1.1 to 90% confidence, almost 400 times the observed flux, and consistent with various multi-wavelength diagnostics. Such a high intrinsic to observed flux ratio in addition to an Fe-Kα fluorescence line equivalent width exceeding 2 keV is extreme amongst known bona fide CTK AGN, which we suggest are both due to the high level of obscuration present around IC 3639. Our study demonstrates that broadband spectroscopic modelling with NuSTAR enables large corrections for obscuration to be carried out robustly, and emphasises the need for improved modelling of AGN tori showing intense iron fluorescence.

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Section: The Targetsupporting

confidence: 53%

“…This is a further reason for the importance of consistent modeling to determine the column density more robustly. Additionally, the errors seem to favor a high EW, with the upper limit fully encapsulating the most extreme cases reported by Levenson et al (2002).…”

Section: Results From Spectral Fittingmentioning

confidence: 72%

IC 3639—A NEW BONA FIDE COMPTON-THICK AGN UNVEILED BY NuSTAR

Boorman

Gandhi

Alexander

et al. 2016

ApJ

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“…4.3 that this effect is indeed expected as many Type-2 emission-line AGN are not seen to produce significant X-ray flux, even in the hard [2-10] keV X-ray bands . This is often interpreted as sources that are heavily absorbed and even Compton-thick (Levenson et al 2002). Although we have corrected for the intrinsic absorption in each individual source, this suggests that there are many obscured X-ray sources, that we simply do not detect.…”

Section: Summary and Discussionmentioning

confidence: 96%

“…Specifically, at z < ∼ 0.1 the normalisation of the AGN luminosity function is different by ∼0.5 dex when using emission-lines and X-ray selection criteria ). In the framework of the unified scheme of AGN these differences were often suggested to be due to the existence of an AGN population which is heavily obscured in the X-ray regime (Levenson et al 2002;Cappi et al 2006). Risaliti et al (1999) reports that 75% of optically selected Seyfert-2 galaxies are heavily obscured (n H > 10 23 cm −2 ), and about half are Compton thick (n H > 10 24 cm −2 ); as shown in Fig.…”

Section: Fraction-mass Relationsmentioning

confidence: 99%

The dependence of X-ray AGN activity on host galaxy properties and environment

Tasse

Röttgering

Best

2010

A&A

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There is mounting evidence that active galactic nuclei (AGN) selected through optical emission lines or radio luminosities comprise two distinct AGN populations, whose activity is triggered by different processes. In two previous papers, we studied the host galaxies and environment of radio-loud AGN. In this third paper we study the properties of a sample of Type-2 AGN that were selected on the basis of their [2-10] keV X-ray luminosity. We find that the X-ray luminosity function is in good agreement with previous studies and that the fraction of galaxies hosting an X-ray AGN is a strong function of the stellar mass of the host galaxy. The shape of this fraction-mass relation is similar to the fraction of galaxies that are emission-line AGN, while it differs significantly from the relation observed for radio-selected AGN. The AGN in our sample tend to be located in underdense environments where galaxy mergers and interactions are likely to occur. For all host galaxy masses, the Type-2 AGN display a strong infrared excess at short (∼3.5 μm) wavelengths, suggesting the presence of hot dust possibly associated with a hot dusty torus. These results add weight to the belief that the X-ray selection criteria identifies a population of AGN similar to the emission-line selected population but distinct from the radio population at high masses.

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“…The presence of a strong narrow Fe Kα line (EW1 keV) is also an indicator for aCompton-thick AGN (e.g., Levenson et al 2002). The Fe line EW is positively correlated with N H (e.g., Leahy & Creighton 1993;Bassani et al 1999;Liu & Wang 2010), since thehigher line-of-sight N H depresses the continuum, but not the line.…”

Section: Narrow Fe Kα Linementioning

confidence: 99%

X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration

Liu

Tozzi²,

Wang

et al. 2017

ApJS

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We present a detailed spectral analysis of the brightest active galactic nuclei (AGNs) identified in the 7Ms Chandra Deep Field-South (CDF-S) survey over a time span of 16 years. Using a model of an intrinsically absorbed power-law plus reflection, with possible soft excess and narrow Fe Kα line, we perform a systematic X-ray spectral analysis, both on the total 7Ms exposure and in four different periods with lengths of 2–21 months. With this approach, we not only present the power-law slopes, column densities , observed fluxes, and absorption-corrected 2–10 keV luminosities L X for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the variabilities can be ascribed to two different types of mechanisms, either flux-driven or flux-independent. We also find that the correlation between the narrow Fe line EW and can be well explained by the continuum suppression with increasing . Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of for the CDF-S AGN population and present reselected subsamples that are complete with respect to . The -complete subsamples enable us to decouple the dependences of on L X and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average and L X of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as .

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Extreme X-Ray Iron Lines in Active Galactic Nuclei

Cited by 85 publications

References 32 publications

IC 3639—A NEW BONA FIDE COMPTON-THICK AGN UNVEILED BY NuSTAR

IC 3639—A NEW BONA FIDE COMPTON-THICK AGN UNVEILED BY NuSTAR

The dependence of X-ray AGN activity on host galaxy properties and environment

X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration

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