M. Brightman

An XMM–Newton spectral survey of 12 μm selected galaxies – I. X-ray data

We present an X-ray spectral analysis of 126 galaxies of the 12 μm galaxy sample. By studying this sample at X-ray wavelengths, we aim to determine the intrinsic power, continuum shape and obscuration level in these sources. We improve upon previous works by the use of superior data in the form of higher signal-to-noise ratio spectra, finer spectral resolution and a broader bandpass from XMM–Newton. We pay particular attention to Compton thick active galactic nucleus (AGN) with the help of new spectral fitting models that we have produced, which are based on Monte Carlo simulations of X-ray radiative transfer, using both a spherical and torus geometry, and taking into account Compton scattering and iron fluorescence. We use this data to show that with a torus geometry, unobscured sightlines can achieve a maximum equivalent width of the Fe Kα line of ∼150 eV, originally shown by Ghisellini et al. In order for this to be exceeded, the line of sight must be obscured with NH > 10 23 cm −2 , as we show for one case, NGC 3690. We also calculate flux suppression factors from the simulated data, the main conclusion from which is that for NH ≥ 10 25 cm −2 , the X-ray flux is suppressed by a factor of at least 10 in all X-ray bands and at all redshifts, revealing the biases present against these extremely heavily obscured systems inherent in all X-ray surveys. Furthermore, we confirm previous results from Murphy & Yaqoob that show that the reflection fraction determined from slab geometries is underestimated with respect to toroidal geometries. For the 12 μm selected galaxies, we investigate the distribution of X-ray power-law indices, finding that the mean (� � �= 1.90 +0.05 −0.07 and σ � = 0.31 +0.05 −0.05 ) is consistent with previous works, and that the distribution = = = =

X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue

Aims. Active galactic nuclei are known to have complex X-ray spectra that depend on both the properties of the accreting super-massive black hole (e.g. mass, accretion rate) and the distribution of obscuring material in its vicinity (i.e. the “torus”). Often however, simple and even unphysical models are adopted to represent the X-ray spectra of AGN, which do not capture the complexity and diversity of the observations. In the case of blank field surveys in particular, this should have an impact on e.g. the determination of the AGN luminosity function, the inferred accretion history of the Universe and also on our understanding of the relation between AGN and their host galaxies. Methods. We develop a Bayesian framework for model comparison and parameter estimation of X-ray spectra. We take into account uncertainties associated with both the Poisson nature of X-ray data and the determination of source redshift using photometric methods. We also demonstrate how Bayesian model comparison can be used to select among ten di erent physically motivated X-ray spectral models the one that provides a better representation of the observations. This methodology is applied to X-ray AGN in the 4 Ms Chandra Deep Field South. Results. For the 350 AGN in that field, our analysis identifies four components needed to represent the diversity of the observed X-ray spectra: (1) an intrinsic power law; (2) a cold obscurer which reprocesses the radiation due to photo-electric absorption, Compton scattering and Fe-K fluorescence; (3) an unabsorbed power law associated with Thomson scattering o ionised clouds; and (4) Compton reflection, most noticeable from a stronger-than-expected Fe-K line. Simpler models, such as a photo-electrically absorbed power law with a Thomson scattering component, are ruled out with decisive evidence (B > 100). We also find that ignoring the Thomson scattering component results in underestimation of the inferred column density, NH, of the obscurer. Regarding the geometry of the obscurer, there is strong evidence against both a completely closed (e.g. sphere), or entirely open (e.g. blob of material along the line of sight), toroidal geometry in favour of an intermediate case. Conclusions. Despite the use of low-count spectra, our methodology is able to draw strong inferences on the geometry of the torus. Simpler models are ruled out in favour of a geometrically extended structure with significant Compton scattering. We confirm the presence of a soft component, possibly associated with Thomson scattering o ionised clouds in the opening angle of the torus. The additional Compton reflection required by data over that predicted by toroidal geometry models, may be a sign of a density gradient in the torus or reflection o the accretion disk. Finally, we release a catalogue of AGN in the CDFS with estimated parameters such as the accretion luminosity in the 2 10 keV band and the column density, NH, of the obscurer.

Obscuration-dependent Evolution of Active Galactic Nuclei

We aim to constrain the evolution of AGN as a function of obscuration using an X-ray selected sample of

CANDELS/GOODS-S, CDFS, and ECDFS: photometric redshifts for normal and x-ray-detected galaxies

\sim2000

A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys

AGN from a multi-tiered survey including the CDFS, AEGIS-XD, COSMOS and XMM-XXL fields. The spectra of individual X-ray sources are analysed using a Bayesian methodology with a physically realistic model to infer the posterior distribution of the hydrogen column density and intrinsic X-ray luminosity. We develop a novel non-parametric method which allows us to robustly infer the distribution of the AGN population in X-ray luminosity, redshift and obscuring column density, relying only on minimal smoothness assumptions. Our analysis properly incorporates uncertainties from low count spectra, photometric redshift measurements, association incompleteness and the limited sample size. We find that obscured AGN with

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

N_{H}>{\rm 10^{22}\, cm^{-2}}

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

account for

Constraining the fraction of Compton-thick AGN in the universe by modelling the diffuse X-ray background spectrum

{77}^{+4}_{-5}\%

The NuSTAR view of nearby compton-thick active galactic nuclei: the cases of NGC 424, NGC 1320, and IC 2560

of the number density and luminosity density of the accretion SMBH population with

Compton thick active galactic nuclei in Chandra surveys

L_{{\rm X}}>10^{43}\text{ erg/s}