The contribution of faint active galactic nuclei to the hard X-ray background

被引:95
作者
Fiore, F
La Franca, F
Giommi, P
Elvis, M
Matt, G
Comastri, A
Molendi, S
Gioia, I
机构
[1] BeppoSAX Sci Data Ctr, I-00131 Rome, Italy
[2] Osserv Astron Roma, I-00044 Monte Porzio Catone, Italy
[3] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[4] Univ Roma Tre, Dipartimento Fis, I-00146 Rome, Italy
[5] Osservatorio Astron Bologna, I-40127 Bologna, Italy
[6] CNR, IFCTR, I-20133 Milan, Italy
[7] CNR, IRA, I-40129 Bologna, Italy
[8] Univ Hawaii, Inst Astron, Honolulu, HI 96822 USA
关键词
surveys; galaxies : active; galaxies : general; X-rays : galaxies;
D O I
10.1046/j.1365-8711.1999.02795.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Hard X-ray selection is the most efficient way to discriminate between accretion-powered sources, such as active galactic nuclei (AGN), and sources dominated by starlight. Hard X-rays are also less affected than other bands by obscuration. We have therefore carried out the BeppoSAX High Energy Large Area Survey (HELLAS) in the largely unexplored 5-10 keV band, finding 180 sources in similar to 50 deg(2) of sky with flux greater than or similar to 5 x 10(-14) ergcm(-2)s(-1). After correction for the non-uniform sky coverage this corresponds to resolving about 30 per cent of the hard cosmic X-ray background (XRB). Here we report on a first optical spectroscopic identification campaign, finding 12 AGN out of 14 X-ray error boxes studied. Seven AGN show evidence for obscuration in X-ray and optical bands, a fraction higher than in previous ROSAT or ASCA-ROSAT surveys (at 95-99 and 90 per cent confidence levels respectively), thus supporting the scenario in which a significant fraction of the XRB is created by obscured AGN.
引用
收藏
页码:L55 / L60
页数:6
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