The Young, the Old, and the Dusty: Stellar Populations of Active Galactic Nucleus Hosts

Draper, Aden R.; Ballantyne, D. R.

doi:10.1088/0004-637x/740/2/57

Cited by 6 publications

(7 citation statements)

References 113 publications

(231 reference statements)

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“…In the local universe it has become widely accepted that this is done by a cold molecular torus surrounding the nucleus on parsec scales. However this picture is not so clear at higher redshifts (Draper & Ballantyne 2011;Page et al 2011). Host galaxy and/or star forming processes have been suggested as possible obscuring scenarios, many of which stem from galaxy/AGN formation models (e.g.…”

Section: Nature Of the Obscurationmentioning

confidence: 99%

Compton thick active galactic nuclei in Chandra surveys

Brightman

Nandra

Salvato

et al. 2014

Monthly Notices of the Royal Astronomical Society

102

135

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We present the results from an X-ray spectral analysis of active galactic nuclei (AGN) in the Chandra Deep Field-South, AEGIS-XD and Chandra-COSMOS surveys, focussing on the identification and characterisation of the most heavily obscured, Compton thick (CT, N H > 10 24 cm −2 ) sources. Our sample is comprised of 3184 X-ray selected extragalactic sources, which has a high rate of redshift completeness ( 97.6%), and includes improved photometric redshifts over previous studies. We use spectral models designed for heavily obscured AGN which self consistently include all major spectral signatures of heavy absorption. We identify CT sources not selected through our spectral fitting method using X-ray colours, validate our spectral fitting method through simulations, and take considerations for the constraints on N H given the low count nature of many of our sources. After these considerations we identify a total of 100 CT AGN with best-fit N H > 10 24 cm −2 and N H constrained to be above 10cm −2 at 90% confidence. These sources cover an intrinsic 2-10 keV X-ray luminosity range of 10 42 − 3 × 10 45 erg s −1 and a redshift range of z=0.1-4. This sample will enable characterisation of these heavily obscured AGN across cosmic time and to ascertain their cosmological significance. These survey fields are sites of extensive multi-wavelength coverage, including near-infrared CANDELS data and far-infrared Herschel data, enabling forthcoming investigations into the host properties of CT AGN. Furthermore, by using the torus models to test different covering factor scenarios, and by investigating the inclusion of the soft scattered emission, we find evidence that the covering factor of the obscuring material decreases with L X for all redshifts, consistent with the receding torus model, and that this factor increases with redshift, consistent with an increase in the obscured fraction towards higher redshifts. The strong relationship between the parameters of obscuration and L X points towards an origin intrinsic to the AGN, however the increase of the covering factor with redshift may point towards contributions to the obscuration by the host galaxy. We make N H , Γ (with uncertainties), observed X-ray fluxes and intrinsic 2-10 keV luminosities for all sources analysed in this work publicly available in an online catalogue.

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Section: Nature Of the Obscurationmentioning

confidence: 99%

Compton thick active galactic nuclei in Chandra surveys

Brightman

Nandra

Salvato

et al. 2014

Monthly Notices of the Royal Astronomical Society

102

135

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“…This unification scheme describes a torus‐like structure, which obscures the central engine for some sight lines, and not for others, producing the two observed AGN types, depending on the orientation of the observer. The torus paradigm of the unified scheme has much observational support in the local Universe, but the relevance of the unified scheme at higher redshifts is not so clear (Draper & Ballantyne 2011; Page et al 2011). Characterizing AGN obscuration, especially at intermediate redshifts and the most extremely obscured, Compton thick ( N H ≥ 1.5 × 10 24 cm −2 ) AGN population, is key in understanding the accretion history of the Universe (Fabian & Iwasawa 1999).…”

Section: Introductionmentioning

confidence: 99%

The evolution of the Compton thick fraction and the nature of obscuration for active galactic nuclei in the Chandra Deep Field South

Brightman

Ueda²

2012

Monthly Notices of the Royal Astronomical Society

107

113

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We present the results from the X-ray spectral analysis of high-redshift active galactic nuclei (AGN) in the Chandra Deep Field South (CDFS), making use of the new 4 Ms data set and new X-ray spectral models from Brightman & Nandra, which account for Compton scattering and the geometry of the circumnuclear material. Our goals are to ascertain to what extent the torus paradigm of local AGN is applicable at earlier epochs and to evaluate the evolution of the Compton thick fraction with redshift, important for X-ray background synthesis models and understanding the accretion history of the Universe. In addition to the torus models, we measure the fraction of scattered nuclear light, f scatt , known to be dependent on the covering factor of the circumnuclear material, and use this to aid in our understanding of its geometry. We find that the covering factor of the circumnuclear material is correlated with the line-ofsight column density N H , and as such the most heavily obscured AGN are in fact also the most geometrically buried. We come to these conclusions from the result that f scatt decreases as N H increases and from the prevalence of the torus model with the smallest opening angle as the best-fitting model in the fits to the most obscured AGN. We find that a significant fraction of sources (∼20 per cent) in the CDFS are likely to be buried in material with close to 4π coverage having been best fitted by the torus model with a 0 • opening angle. Furthermore, we find 41 Compton thick sources in the CDFS using the new torus models, 29 of which we report here for the first time. We bin our sample by redshift in order to investigate the evolution of the Compton thick fraction by epoch. We take into account the incompleteness and contamination rates in the spectral identification of Compton thick AGN using data from simulations. We also account for the bias against the X-ray selection of heavily obscured sources due to flux suppression in the Chandra band, by restricting to intrinsic luminosities at which the CDFS is sensitive to Compton thick AGN (L X ∼ 10 44 at z = 2.5). We find a significant increase in the intrinsic Compton thick fraction, normalized to L X = 10 43.5 erg s −1 , from ≈20 per cent in the local Universe to ≈40 per cent at z = 1−4.

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“…In the past decade, several authors focused their attention on the relation between the nuclear activity and the star formation rate (Ivanov et al 2000;González Delgado et al 2001;Joguet et al 2001;Ho et al 2003;La Mura et al 2009;Draper & Ballantyne 2011;Cracco et al 2011;Vaona et al 2012). This relation can give important clues about the fate of the gas that fuels the central black hole (Hopkins & Hernquist 2006) and its influence on the central part of the host galaxy (Sarzi et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Stellar population properties for a sample of hard X-ray AGNs

Morelli

Calvi

Masetti

et al. 2013

A&A

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Aims. The aim of this paper is to study the stellar population of galaxies hosting an active galactic nucleus (AGN). We studied a subsample of hard X-ray emitting AGNs from the INTEGRAL and Swift catalogs, which were previously identified and characterized through optical spectroscopy. Our analysis provides complementary information, namely age and metallicity, which is necessary to complete the panoramic view of these interesting objects. Methods. We selected hard X-ray emitting objects, identified as AGNs, by checking their optical spectra in search of absorption lines suitable for the stellar population analysis. We obtained a final sample consisting of 20 objects with a redshift lower than 0.3. We used the full-spectrum fitting method; particularly, we use penalized pixel method and apply the PPXF code. After masking all the regions affected by emission lines, we fitted the spectra with the MILES single stellar population templates, and we derived mass-weighted ages and metallicities. Results. Most of the objects in our sample show an old stellar population; however, three of them are characterized by a bimodal distribution with a non-negligible contribution from young stars. The values of the mass-weighted metallicity span a wide range with most of them slightly above the solar value. No relations between the stellar population properties and the morphological ones have been found.

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The Young, the Old, and the Dusty: Stellar Populations of Active Galactic Nucleus Hosts

Cited by 6 publications

References 113 publications

Compton thick active galactic nuclei in Chandra surveys

Compton thick active galactic nuclei in Chandra surveys

The evolution of the Compton thick fraction and the nature of obscuration for active galactic nuclei in the Chandra Deep Field South

Stellar population properties for a sample of hard X-ray AGNs

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