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

被引：39
作者：
Moretti, A. [1 ]
Vattakunnel, S. [2 ]
Tozzi, P. [2 ]
Salvaterra, R. [3 ]
Severgnini, P. [1 ]
Fugazza, D. [1 ]
Haardt, F. [4 ,5 ]
Gilli, R. [6 ]
机构：
[1] Osserv Astron Brera, INAF, I-20121 Milan, Italy
[2] Osserv Astron Trieste, INAF, I-34143 Trieste, Italy
[3] Ist Astrofis Spaziale & Fis Cosm, INAF, I-20133 Milan, Italy
[4] Univ Insubria, DiSAT, I-22100 Como, Italy
[5] Ist Nazl Fis Nucl, Sez Milano Bicocca, I-20126 Milan, Italy
[6] Osserv Astron Brera, INAF, I-40127 Bologna, Italy
来源：
ASTRONOMY & ASTROPHYSICS | 2012年 / 548卷
基金：
美国国家航空航天局;
关键词：
X-rays: diffuse background; X-rays: general; galaxies: active; ACTIVE GALACTIC NUCLEI; DEEP FIELD-SOUTH; MS SOURCE CATALOGS; XMM-NEWTON; LUMINOSITY FUNCTION; NUMBER COUNTS; MASSIVE GALAXIES; BLACK-HOLES; CHANDRA; REDSHIFT;
D O I：
10.1051/0004-6361/201219921
中图分类号：
P1 [天文学];
学科分类号：
0704 ;
摘要：
Aims: 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. Methods. 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. Results. 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(-2.6)(+3.2) x 10(-12) erg s(-1) cm(-2) deg(-2) 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. Conclusions. 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.
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页数：11
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