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Nature of Hard X-ray Source from Optical Identification of the ASCA Large Sky Survey

M. Akiyama·K. Ohta·T. Yamada·Y. Ueda·T. Takahashi·M. Sakano·T. Tsuru·I. Lehmann·G. Hasinger
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Abstract

We present results of optical identification of the ASCA Large Sky Survey. X-ray sources which have hard X-ray spectra were identified with type-2 AGN at redshifts smaller than 0.5. It is supported that the absorbed X-ray spectrum of type-2 AGN makes the Cosmic X-ray Background harder in the hard X-ray band than type-1 AGN, which is main contributer in the soft X-ray band. Absence of type-2 AGN at redshift larger than 1 in the identified sample, which contrasts to the existence of 6 broad-line QSOs, suggests a deficiency of so-called ``type-2 QSO'' at high redshift.

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M. Akiyama, K. Ohta, T. Yamada, Y. Ueda, T. Takahashi, M. Sakano, T. Tsuru, I. Lehmann, G. Hasinger. 1998-11-02. Nature of Hard X-ray Source from Optical Identification of the ASCA Large Sky Survey. https://doi.org/10.1002/1521-3994(199908)320%3A4%2F5%3C255%3A%3Aaid-asna255%3E3.0.co%3B2-s

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