The Shape of the Cosmic X-ray Background: Nuclear Starburst Discs and the Redshift Evolution of AGN Obscuration

Abstract

A significant number of active galactic nuclei (AGNs) are observed to be hidden behind dust and gas. The distribution of material around AGNs plays an important role in modeling the cosmic X-ray background (CXB), especially the fraction of Type-2 AGNs ($f_2$). One of the possible explanations for the obscuration in Seyfert galaxies at intermediate redshift is dusty starburst discs. We compute the 2D hydrostatic structure of 768 nuclear starburst discs (NSDs) under various physical conditions and also the distribution of column density along the line of sight ($N_{\text{H}}$) associated with these discs. Then, the $N_{\text{H}}$ distribution is evolved with redshift by using the redshift dependent distribution function of input parameters. The $f_2$ shows a strong positive evolution up to $z=2$, but only a weak level of enhancement at higher $z$. The Compton-thin and Compton-thick AGN fractions associated with these starburst regions increase as $\propto (1+z{)}^{\delta }$ where the $\delta$ is estimated to be 1.12 and 1.45, respectively. The reflection parameter $R_f$ associated with column density $N_{\text{H}}\ge 10^{23.5}$ cm${}^{-2}$ extends from 0.13 at $z=0$ to 0.58 at $z=4$. A CXB model employing this evolving $N_{\text{H}}$ distribution indicates more compact ($R_{\text{out}}<120$ pc) NSDs provide a better fit to the CXB. In addition to "Seyfert-like" AGNs obscured by nuclear starbursts, we predict that 40 to 60 per cent of quasars must be Compton-thick to produce the peak of the CXB spectrum within observational uncertainty. The predicted total number counts of AGNs in 8-24 keV band are in fair agreement with observations from NuSTAR.

accepted by MNRAS

References in corpus (27)

• Cosmic Star Formation History
• Star Formation in AEGIS Field Galaxies since z=1.1 : The Dominance of Gradually Declining Star Formation, and the Main Sequence of Star-Forming Galaxies
• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• Absorption Properties and Evolution of Active Galactic Nuclei
• The Discovery of 1000 km/s Outflows in Massive Post-starburst Galaxies at z=0.6
• The close environments of accreting massive black holes are shaped by radiative feedback
• Obscuration-dependent evolution of Active Galactic Nuclei
• The Luminosity Function of X-ray Selected Active Galactic Nuclei: Evolution of Supermassive Black Holes at High Redshift
• Quasars Are Not Light-Bulbs: Testing Models of Quasar Lifetimes with the Observed Eddington Ratio Distribution
• A new method for determining the sensitivity of X-ray imaging observations and the X-ray number counts
• AGN dust tori at low and high luminosities
• High-Velocity Outflows Without AGN Feedback: Eddington-Limited Star Formation in Compact Massive Galaxies
• Chandra Multiwavelength Project X-ray Point Source Number Counts and the Cosmic X-ray Background
• XMM and Chandra measurements of the AGN intrinsic absorption: dependence on luminosity and redshift
• The Chandra COSMOS legacy survey: Energy Spectrum of the Cosmic X-ray Background and constraints on undetected populations
• The XMM-Newton Serendipitous Survey. VI. The X-ray Luminosity Function
• The Hard X-Ray Luminosity Function of High-Redshift ($3<z\lesssim 5$) Active Galactic Nuclei
• Obscuring Active Galactic Nuclei with Nuclear Starburst Disks
• Warping and precession in galactic and extragalactic accretion disks
• The NuSTAR Serendipitous Survey: Hunting for The Most Extreme Obscured AGN at >10 keV
• Evidence for a large fraction of Compton-thick quasars at high redshift
• Does the AGN Unified Model Evolve with Redshift? Utilizing the X-ray Background to Predict the Mid-Infrared Emission of AGN
• Bright end of the luminosity function of high-mass X-ray binaries: contributions of hard, soft and supersoft sources
• The NuSTAR Extragalactic Survey: Average broad-band X-ray spectral properties of the NuSTAR detected AGN
• Most hard X-ray selected quasars in Chandra Deep Fields are obscured
• Modeling the Vertical Structure of Nuclear Starburst Discs: A Possible Source of AGN Obscuration at $z\sim 1$

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• NuSTAR and Keck Observations of Heavily Obscured Quasars Selected by WISE
• Measuring the Cosmic X-ray Background in 3-20keV with Straylight from NuSTAR
• On The Fine Tuning and Physical Origin of Line-Locked Absorption Systems in Active Galaxies
• The stellar remnants of high redshift nuclear starburst discs: a potential origin for nuclear star clusters?