The unresolved hard X-ray background: the missing source population implied by the Chandra and XMM--Newton deep fields

Worsley, Marcus A.; Fabian, A. C.; Bauer, F. E.; Alexander, D. M.; Hasinger, G.; Mateos, S.; Brunner, H.; Brandt, W. N.; Schneider, Donald P.

doi:10.1111/j.1365-2966.2005.08731.x

Cited by 203 publications

(243 citation statements)

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“…Analytical calculations (Valageas et al 2002) and numerical simulations predict that the WHIM contributes between a few per cent (Kang et al 2005) and 40 per cent (Croft et al 2001;Roncarelli et al 2006) of the total X-ray background emission, consistent with the observational upper limit of (1.2 ± 0.3) × 10 −12 erg s −1 cm −2 deg −2 (Worsley et al 2005). Because of the softness of the spectrum, the WHIM produces only between 4 per cent (Croft et al 2001) and 10 per cent (Roncarelli et al 2006) of the total hard X-ray emission.…”

Section: Whim Contribution To the Soft X-ray Backgroundmentioning

confidence: 80%

“…Since most of the observed background emission has been resolved into point sources (Hasinger et al 1998;Worsley et al 2005), the comparison of the predictions of hydrodynamical simulations with observations can put tight constraints on the amount of the observed background emission that can be attributed to the diffuse intergalactic gas.…”

Section: Non-equilibrium Calculationsmentioning

confidence: 99%

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Numerical Simulations of the Warm-Hot Intergalactic Medium

2008

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In this paper we review the current predictions of numerical simulations for the origin and observability of the warm hot intergalactic medium (WHIM), the diffuse gas that contains up to 50 per cent of the baryons at z ∼ 0. During structure formation, gravitational accretion shocks emerging from collapsing regions gradually heat the intergalactic medium (IGM) to temperatures in the range T ∼ 10 5 -10 7 K. The WHIM is predicted to radiate most of its energy in the ultraviolet (UV) and X-ray bands and to contribute a significant fraction of the soft X-ray background emission. While O VI and C IV absorption systems arising in the cooler fraction of the WHIM with T ∼ 10 5 -10 5.5 K are seen in FUSE and Hubble Space Telescope observations, models agree that current X-ray telescopes such as Chandra and XMM-Newton do not have enough sensitivity to detect the hotter WHIM. However, future missions such as Constellation-X and XEUS might be able to detect both emission lines and absorption systems from highly ionised atoms such as O VII, O VIII and Fe XVII.

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Section: Whim Contribution To the Soft X-ray Backgroundmentioning

confidence: 80%

Section: Non-equilibrium Calculationsmentioning

confidence: 99%

Numerical Simulations of the Warm-Hot Intergalactic Medium

2008

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“…non-local AGN (Worsley et al 2005;Xue et al 2012). It is therefore crucial to directly investigate the distribution of the obscured AGN population at the high column densities contributing to the CXB at high energies.…”

Section: Introductionmentioning

confidence: 99%

The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

Zappacosta

Comastri

Civano

et al. 2018

ApJ

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We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S 8 24 keV 7 10 14 =´-( -) erg s cm 1 2 --in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z 0 2.1 = -(median z 0.58 á ñ = ). The spectral analysis is performed over the broad 0.5-24keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at 10 keV > to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density (N H ), reflection parameter (R), and 10-40keV luminosity (L X ). Heavily obscured ( N log cm 23AGN constitute ∼25% (15-17 sources) and ∼2-3% (1-2 sources) of the sample, respectively. The observed N H distribution agrees fairly well with predictions of cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of N H , accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to N log cm 20 24AGN is poorly constrained, formally in the range 2-56% (90% upper limit of 66%). We derived a fraction ( f abs ) of obscured AGN ( N log cm 22 24as a function of L X in agreement with CXBPSM and previous z 1 < X-ray determinations. Furthermore, f abs at z 0.1 0.5 = -and L log erg s 43.6 44.3agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of R with L X (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values.

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“…Thus X-ray observations have long indicated there is a large population of heavily obscured AGN (Setti & Woltjer 1989;Comastri et al 1995;Gilli et al 2001). While much of the X-ray background has been resolved at low energies, recent work on X-ray deep fields suggests the hardest (most obscured) X-ray sources have yet to be detected (e.g., Worsley et al 2005).…”

Section: Cosmic Growth Of Black Holes and Galaxiesmentioning

confidence: 99%

Supermassive black holes in deep multiwavelength surveys

Urry¹,

Treister²

2011

Black Holes

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In recent years deep X-ray and infrared surveys have provided an efficient way to find accreting supermassive black holes, otherwise known as active galactic nuclei (AGN), in the young universe. Such surveys can, unlike optical surveys, find AGN obscured by high column densities of gas and dust. In those cases, deep optical data show only the host galaxy, which can then be studied in greater detail than in unobscured AGN. Some years ago the hard spectrum of the Xray "background" suggested that most AGN were obscured. Now GOODS, MUSYC, COSMOS and other surveys have confirmed this picture and given important quantitative constraints on AGN demographics. Specifically, we show that most AGN are obscured at all redshifts and the amount of obscuration depends on both luminosity and redshift, at least out to redshift z ∼ 2, the epoch of substantial black holes and galaxy growth. Larger-area deep infrared and hard X-ray surveys will be needed to reach higher redshifts and to probe fully the co-evolution of galaxies and black holes. Cosmic Growth of Black Holes and GalaxiesAbundant evidence indicates that the growth of a supermassive black hole is closely tied to the formation and evolution of the surrounding galaxy. The energy released from accretion onto the black hole affects star formation in the galaxy, probably limiting growth at the high-and low-mass ends, and of course the distribution and angular momentum of matter in the galaxy governs the amount of matter accumulated by the black hole (Silk & Rees 1998;King 2005;Rovilos et al. 2007). Emergent energy from accretion is also a factor in understanding ionization and radiation backgrounds (Hasinger 2000;Lawrence 2001). Understanding the growth history of these black holes is therefore critical to understanding the global evolution of structure in the Universe.Yet the demographics of supermassive black holes remain elusive. The largest samples of quasars and Active Galactic Nuclei (AGN), by which we mean supermassive black holes in a high accretion-rate phase †, have been found through optical selection (e.g., the Sloan Digital Sky Survey quasar sample; Schneider et al. 2002Schneider et al. , 2007, but, at least locally, these are not representative of the larger AGN population. Instead we need surveys less biased against obscured AGN.There are three reasons to suspect that most AGN are obscured by large column densities of gas and dust. First, a large body of evidence suggests that local AGN have geometries that are not spherically symmetric, and that different aspect angles present markedly different observed characteristics; this is referred to as AGN unification (Antonucci 1993;Urry & Padovani 1995). Second, AGN are more common at high redshift (z ∼ 2 − 3), where the average star formation rate is higher and thus it is even more likely that gas and dust surround the galaxy nucleus than at z ∼ 0. Third, and most important, obscured AGN are required to explain the shape of the X-ray "background" radiation.The X-ray "background" is actually the superposition of ind...

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The unresolved hard X-ray background: the missing source population implied by the Chandra and XMM--Newton deep fields

Cited by 203 publications

References 40 publications

Numerical Simulations of the Warm-Hot Intergalactic Medium

Numerical Simulations of the Warm-Hot Intergalactic Medium

The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

Supermassive black holes in deep multiwavelength surveys

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