Spectrum of the unresolved cosmic X ray background: what is unresolved 50 years after its discovery

Abstract

We study the spectral properties of the unresolved cosmic X-ray background (CXRB) in the 1.5-7.0 keV energy band with the aim of providing an observational constraint on the statistical properties of those sources that are too faint to be individually probed. We made use of the Swift X-ray observation of the Chandra Deep Field South complemented by the Chandra data. Exploiting the lowest instrument background (Swift) together with the deepest observation ever performed (Chandra) we measured the unresolved emission at the deepest level and with the best accuracy available today. We find that the unresolved CXRB emission can be modeled by a single power law with a very hard photon index Gamma=0.1+/-0.7 and a flux of 5(+/-3)E-12 cgs in the 2.0-10 keV energy band (1 sigma error). Thanks to the low instrument background of the Swift-XRT, we significantly improved the accuracy with respect to previous measurements. These results point towards a novel ingredient in AGN population synthesis models, namely a positive evolution of the Compton-thick AGN population from local Universe to high redshift.

11 pages 12 figures; A&A in press

References in corpus (16)

• A luminous quasar at a redshift of z = 7.085
• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• X-ray spectral properties of AGN in the Chandra Deep Field South
• Absorption Properties and Evolution of Active Galactic Nuclei
• Multiwavelength study of massive galaxies at z~2. II. Widespread Compton thick AGN and the concurrent growth of black holes and bulges
• The GOODS-MUSIC sample: a multicolour catalog of near-IR selected galaxies in the GOODS-South field
• Reliable Identification of Compton-thick Quasars at z~2: Spitzer Mid-IR spectroscopy of HDF-oMD49
• Constraints on X-ray Emissions from the Reionization Era
• XMM and Chandra measurements of the AGN intrinsic absorption: dependence on luminosity and redshift
• The cosmological properties of AGN in the XMM-Newton Hard Bright Survey
• The nature of the unresolved extragalactic soft CXB
• Tracking Down the Source Population Responsible for the Unresolved Cosmic 6-8 keV Background
• Limits on the high redshift growth of massive black holes
• Does the AGN Unified Model Evolve with Redshift? Utilizing the X-ray Background to Predict the Mid-Infrared Emission of AGN
• Unresolved X-ray background: clues on galactic nuclear activity at z>6
• Can the unresolved X-ray background be explained by emission from the optically-detected faint galaxies of the GOODS project?

Cited by in corpus (35)

• Cosmic Reionization after Planck: Could Quasars Do It All?
• Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact Binaries
• The X-ray spectra of the first galaxies: 21cm signatures
• The redshift evolution of escape fraction of hydrogen ionizing photons from galaxies
• Constraining the primordial initial mass function with stellar archaeology
• Radiative Feedback from high mass X-ray binaries on the formation of the first galaxies and early reionization
• Infrared background signatures of the first black holes
• The Chandra COSMOS legacy survey: Energy Spectrum of the Cosmic X-ray Background and constraints on undetected populations
• Searching for the 3.5 keV Line in the Deep Fields with Chandra: the 10 Ms observations
• The XMM deep survey in the CDFS IV. Candidate Compton-thick AGN
• Constraining the redshifted 21-cm signal with the unresolved soft X-ray background
• New observational Constraints on the Growth of the First Supermassive Black Holes
• Unveiling the nature of the unidentified gamma-ray sources IV: the $\text{Swift}$ catalog of potential X-ray counterparts
• The Chandra Deep Fields: Lifting the Veil on Distant Active Galactic Nuclei and X-Ray Emitting Galaxies
• The impact of spin temperature fluctuations on the 21-cm moments
• Constraints on QSO emissivity using H I and He II Lyman alpha forest
• On the Physical Requirements for a Pre-Reionization Origin of the Unresolved Near-Infrared Background
• High redshift AGNs and HI reionisation: limits from the unresolved X-ray background
• The Entire Virial Radius of the Fossil Cluster RXJ1159+5531: I. Gas Properties
• The space density of Compton-thick AGN at z~0.8 in the zCOSMOS-Bright Survey
• Population III X-ray Binaries and their Impact on the Early Universe
• Constraining the Contribution of Galaxies and Active Galactic Nuclei to Cosmic Reionization
• X-ray background and its correlation with the 21 cm signal
• Can AGN and galaxy clusters explain the surface brightness fluctuations of the cosmic X-ray background?
• The dependency of AGN infrared color-selection on source luminosity and obscuration: An observational perspective in CDFS and COSMOS
• Triggering the formation of direct collapse black holes by their congeners
• Measuring the Cosmic X-ray Background in 3-20keV with Straylight from NuSTAR
• A New Multi-Wavelength Census of Blazars
• Constraining the AGN luminosity function from JWST with the X-ray Background
• Probing the physical properties of the intergalactic medium using gamma-ray bursts
• COSMOS2020: Investigating the AGN-obscured accretion phase at $z\sim 1$ via [NeV] selection
• The Swift X-ray Telescope Cluster Survey II. X-ray spectral analysis
• Degeneracy breakdown as a source of supernovae Ia
• The flat entropy profile at the outskirts of the Abell 2244 galaxy cluster
• A Chandra view of SPT-CL J0217-5014: a massive galaxy cluster at a cosmic intersection at z=0.53