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Optical Identification of the ASCA Large Sky Survey

M. Akiyama·K. Ohta·T. Yamada·N. Kashikawa·M. Yagi·W. Kawasaki·M. Sakano·T. Tsuru·Y. Ueda·T. Takahashi·I. Lehmann·G. Hasinger·W. Voges
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Abstract

We present results of optical identification of the X-ray sources detected in the ASCA Large Sky Survey. Optical spectroscopic observations were done for 34 X-ray sources which were detected with the SIS in the 2-7 keV band above 3.5 sigma. The sources are identified with 30 AGNs, 2 clusters of galaxies, and 1 galactic star. Only 1 source is still unidentified. The flux limit of the sample corresponds to 1 x 10^{-13} erg s^{-1} cm^{-2} in the 2-10 keV band. Based on the sample, the paper discusses optical and X-ray spectral properties of the AGNs, contribution of the sources to the Cosmic X-ray Background, and redshift and luminosity distributions of the AGNs. An interesting result is that the redshift distribution of the AGNs suggests a deficiency of high-redshift (0.5 < z < 2) and luminous (Lx(2-10 keV) > 10^{44} erg s^{-1}) absorbed narrow-line AGNs (so called type 2 QSOs).

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M. Akiyama, K. Ohta, T. Yamada, N. Kashikawa, M. Yagi, W. Kawasaki, M. Sakano, T. Tsuru, Y. Ueda, T. Takahashi, I. Lehmann, G. Hasinger, W. Voges. 2000-01-17. Optical Identification of the ASCA Large Sky Survey. https://doi.org/10.1086/308606

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