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An Iwasawa-Taniguchi effect for Compton-thick active galactic nuclei

An Iwasawa-Taniguchi effect for Compton-thick active galactic nuclei
An Iwasawa-Taniguchi effect for Compton-thick active galactic nuclei

We present the first study of an Iwasawa-Taniguchi/'X-ray Baldwin' effect for Compton-thick active galactic nuclei (AGN). We report a statistically significant anticorrelation between the rest-frame equivalent width (EW)of the narrowcore of the neutral FeKα fluorescence emission line, ubiquitously observed in the reflection spectra of obscured AGN, and the mid-infrared 12 μm continuum luminosity (taken as a proxy for the bolometric AGN luminosity). Our sample consists of 72 Compton-thick AGN selected from pointed and deep-field observations covering a redshift range of z ~ 0.0014-3.7.We employ a Monte Carlo-based fitting method, which returns a Spearman's Rank correlation coefficient of ρ = -0.28 ± 0.12, significant to 98.7 per cent confidence. The best-fitting found is log(EWFeKα) ∝ -0.08 ± 0.04 log(L12μm), which is consistent with multiple studies of theX-ray Baldwin effect for unobscured and mildly obscured AGN. This is an unexpected result, as the FeKα line is conventionally thought to originate from the same region as the underlying reflection continuum, which together constitute the reflection spectrum.We discuss the implications this could have if confirmed on larger samples, including a systematic underestimation of the line-of-sight X-ray obscuring column density and hence the intrinsic luminosities and growth rates for the most luminous AGN.

Galaxies: Active, Infrared: Galaxies -X-rays: Galaxies
0035-8711
3775-3790
Boorman, Peter G.
e5240793-37c1-4b7b-9840-3b996cef8dd3
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Baloković, Mislav
159e512c-06ea-4b1c-b580-ec41392aeb3c
Brightman, Murray
57cbed53-6026-477c-be63-e670ab4e36cf
Harrison, Fiona
d12bd352-3538-4dac-86fb-f13bc5837016
Ricci, Claudio
47c48bd5-233e-41dd-824a-3df26357d84f
Stern, Daniel
2eae31a8-424f-4084-837e-ce12a4d00437
Boorman, Peter G.
e5240793-37c1-4b7b-9840-3b996cef8dd3
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Baloković, Mislav
159e512c-06ea-4b1c-b580-ec41392aeb3c
Brightman, Murray
57cbed53-6026-477c-be63-e670ab4e36cf
Harrison, Fiona
d12bd352-3538-4dac-86fb-f13bc5837016
Ricci, Claudio
47c48bd5-233e-41dd-824a-3df26357d84f
Stern, Daniel
2eae31a8-424f-4084-837e-ce12a4d00437

Boorman, Peter G., Gandhi, Poshak, Baloković, Mislav, Brightman, Murray, Harrison, Fiona, Ricci, Claudio and Stern, Daniel (2018) An Iwasawa-Taniguchi effect for Compton-thick active galactic nuclei. Monthly Notices of the Royal Astronomical Society, 477 (3), 3775-3790. (doi:10.1093/mnras/sty861).

Record type: Article

Abstract

We present the first study of an Iwasawa-Taniguchi/'X-ray Baldwin' effect for Compton-thick active galactic nuclei (AGN). We report a statistically significant anticorrelation between the rest-frame equivalent width (EW)of the narrowcore of the neutral FeKα fluorescence emission line, ubiquitously observed in the reflection spectra of obscured AGN, and the mid-infrared 12 μm continuum luminosity (taken as a proxy for the bolometric AGN luminosity). Our sample consists of 72 Compton-thick AGN selected from pointed and deep-field observations covering a redshift range of z ~ 0.0014-3.7.We employ a Monte Carlo-based fitting method, which returns a Spearman's Rank correlation coefficient of ρ = -0.28 ± 0.12, significant to 98.7 per cent confidence. The best-fitting found is log(EWFeKα) ∝ -0.08 ± 0.04 log(L12μm), which is consistent with multiple studies of theX-ray Baldwin effect for unobscured and mildly obscured AGN. This is an unexpected result, as the FeKα line is conventionally thought to originate from the same region as the underlying reflection continuum, which together constitute the reflection spectrum.We discuss the implications this could have if confirmed on larger samples, including a systematic underestimation of the line-of-sight X-ray obscuring column density and hence the intrinsic luminosities and growth rates for the most luminous AGN.

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An Iwasawa-Taniguchi effect for Compton-thick active galactic nuclei - Accepted Manuscript
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More information

Accepted/In Press date: 29 March 2018
e-pub ahead of print date: 5 April 2018
Published date: 1 July 2018
Keywords: Galaxies: Active, Infrared: Galaxies -X-rays: Galaxies

Identifiers

Local EPrints ID: 421384
URI: http://eprints.soton.ac.uk/id/eprint/421384
ISSN: 0035-8711
PURE UUID: 4e6d17ce-f1c6-49fc-b989-db91423fc29b
ORCID for Peter G. Boorman: ORCID iD orcid.org/0000-0001-9379-4716
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 07 Jun 2018 16:30
Last modified: 17 Dec 2019 01:34

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