Abstract
Using Chandra observations in the 2.15 deg2 COSMOS-legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the [0.3-7] keV energy band. The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT ∼ 0.27 and 0.07 keV and an extragalactic power law with a photon spectral index Γ = 1.45 - 0.02. The 1 keV normalization of the extragalactic component is 10.91 - 0.16 keV cm-2 s-1 sr-1 keV-1. Removing all X-ray-detected sources, the remaining unresolved CXB is best fit by a power law with normalization 4.18 - 0.26 keV cm-2 s-1 sr-1 keV-1 and photon spectral index Γ = 1.57 - 0.10. Removing faint galaxies down to leaves a hard spectrum with and a 1 keV normalization of ∼1.37 keV cm-2 s-1 sr-1 keV-1. This means that ∼91% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute ∼8%-9% of the total CXB show marginal evidence of being harder and possibly more obscured than resolved sources. Another ∼1% of the CXB can be attributed to still undetected star-forming galaxies and absorbed active galactic nuclei. According to these limits, we investigate a scenario where early black holes totally account for non-source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the accreted mass density, such a population of black holes must grow in Compton-thick envelopes with 1.6 - 1025 cm-2 and form in extremely low-metallicity environments.
| Original language | English (US) |
|---|---|
| Article number | 19 |
| Journal | Astrophysical Journal |
| Volume | 837 |
| Issue number | 1 |
| DOIs | |
| State | Published - Mar 1 2017 |
| Externally published | Yes |
Fingerprint
Keywords
- catalogs
- infrared: diffuse background
- quasars: supermassive black holes
- surveys
- X-rays: diffuse background
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
Cite this
The Chandra COSMOS Legacy Survey : Energy Spectrum of the Cosmic X-Ray Background and Constraints on Undetected Populations. / Cappelluti, Nico; Li, Yanxia; Ricarte, Angelo; Agarwal, Bhaskar; Allevato, Viola; Ananna, Tonima Tasnim; Ajello, Marco; Civano, Francesca; Comastri, Andrea; Elvis, Martin; Finoguenov, Alexis; Gilli, Roberto; Hasinger, Günther; Marchesi, Stefano; Natarajan, Priyamvada; Pacucci, Fabio; Treister, E.; Urry, C. Megan.
In: Astrophysical Journal, Vol. 837, No. 1, 19, 01.03.2017.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The Chandra COSMOS Legacy Survey
T2 - Energy Spectrum of the Cosmic X-Ray Background and Constraints on Undetected Populations
AU - Cappelluti, Nico
AU - Li, Yanxia
AU - Ricarte, Angelo
AU - Agarwal, Bhaskar
AU - Allevato, Viola
AU - Ananna, Tonima Tasnim
AU - Ajello, Marco
AU - Civano, Francesca
AU - Comastri, Andrea
AU - Elvis, Martin
AU - Finoguenov, Alexis
AU - Gilli, Roberto
AU - Hasinger, Günther
AU - Marchesi, Stefano
AU - Natarajan, Priyamvada
AU - Pacucci, Fabio
AU - Treister, E.
AU - Urry, C. Megan
PY - 2017/3/1
Y1 - 2017/3/1
N2 - Using Chandra observations in the 2.15 deg2 COSMOS-legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the [0.3-7] keV energy band. The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT ∼ 0.27 and 0.07 keV and an extragalactic power law with a photon spectral index Γ = 1.45 - 0.02. The 1 keV normalization of the extragalactic component is 10.91 - 0.16 keV cm-2 s-1 sr-1 keV-1. Removing all X-ray-detected sources, the remaining unresolved CXB is best fit by a power law with normalization 4.18 - 0.26 keV cm-2 s-1 sr-1 keV-1 and photon spectral index Γ = 1.57 - 0.10. Removing faint galaxies down to leaves a hard spectrum with and a 1 keV normalization of ∼1.37 keV cm-2 s-1 sr-1 keV-1. This means that ∼91% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute ∼8%-9% of the total CXB show marginal evidence of being harder and possibly more obscured than resolved sources. Another ∼1% of the CXB can be attributed to still undetected star-forming galaxies and absorbed active galactic nuclei. According to these limits, we investigate a scenario where early black holes totally account for non-source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the accreted mass density, such a population of black holes must grow in Compton-thick envelopes with 1.6 - 1025 cm-2 and form in extremely low-metallicity environments.
AB - Using Chandra observations in the 2.15 deg2 COSMOS-legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the [0.3-7] keV energy band. The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT ∼ 0.27 and 0.07 keV and an extragalactic power law with a photon spectral index Γ = 1.45 - 0.02. The 1 keV normalization of the extragalactic component is 10.91 - 0.16 keV cm-2 s-1 sr-1 keV-1. Removing all X-ray-detected sources, the remaining unresolved CXB is best fit by a power law with normalization 4.18 - 0.26 keV cm-2 s-1 sr-1 keV-1 and photon spectral index Γ = 1.57 - 0.10. Removing faint galaxies down to leaves a hard spectrum with and a 1 keV normalization of ∼1.37 keV cm-2 s-1 sr-1 keV-1. This means that ∼91% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute ∼8%-9% of the total CXB show marginal evidence of being harder and possibly more obscured than resolved sources. Another ∼1% of the CXB can be attributed to still undetected star-forming galaxies and absorbed active galactic nuclei. According to these limits, we investigate a scenario where early black holes totally account for non-source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the accreted mass density, such a population of black holes must grow in Compton-thick envelopes with 1.6 - 1025 cm-2 and form in extremely low-metallicity environments.
KW - catalogs
KW - infrared: diffuse background
KW - quasars: supermassive black holes
KW - surveys
KW - X-rays: diffuse background
UR - http://www.scopus.com/inward/record.url?scp=85015154606&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85015154606&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/aa5ea4
DO - 10.3847/1538-4357/aa5ea4
M3 - Article
VL - 837
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 19
ER -