Optical Identification of theASCALarge Sky Survey

We present results of optical identification of the X-ray sources detected inthe ASCA Large Sky Survey. Optical spectroscopic observations were done for 34X-ray sources which were detected with the SIS in the 2-7 keV band above 3.5sigma. The sources are identified with 30 AGNs, 2 clusters of galaxies, and 1galactic star. Only 1 source is still unidentified. The flux limit of thesample 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 spectralproperties of the AGNs, contribution of the sources to the Cosmic X-rayBackground, and redshift and luminosity distributions of the AGNs. Aninteresting result is that the redshift distribution of the AGNs suggests adeficiency 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).Comment: Accepted for publication in ApJ. 57 pages with 13 figures, 9 JPG plates, 5 additional PS tables. Original EPS plates (gzipped format ~1Mbyte/plate) and TeX tables are available from ftp://ftp.kusastro.kyoto-u.ac.jp/pub/akiyama/0001289