ASCA deep survey in the Lockman Hole Field

We present the results of deep observations of the Lockman Hole field with the ASCA SIS, covering 926 arcmin(2) in the 1-7keV energy range, with a sensitivity 3-5 times deeper than the previous ASCA larger area surveys. Utilizing the results of the ROSAT Ultra Deep survey, we have detected 32, 25, and 15 sources in the 1-7, 1-2, and 2-7 keV bands, and only 4, 4, and 1 sources remain unidentified, respectively. The average hardness of the sources detected in the 1-7 keV band with fluxes of between 10(-14) and 10(-13) erg cm(-2) s(-1) corresponds to a photon index of 1.65 +/- 0.10. Type-2 AGNs show significantly harder spectra than type-is, which can be explained by absorption column densities of N-H similar or equal to 10(22-23) cm(-2) at the source redshifts. Fifteen sources are detected in the hard-band (2-7 keV), consisting of six type-1 AGNs, six type-2 AGNs, one star, one cluster of galaxies, and one unidentified source. Type-2 AGNs make up a major part of hard X-ray populations in the 2-7 keV band at a flux level of 3 x 10(-14) erg cm(-2) s(-1) (2-7 keV). The redshift distributions of type-1 and type-2 AGNs suggest a lack of high luminosity (optically-defined) type-2 AGNs with intrinsic N-H < 10(23) Cm-2, in the redshift range z similar or equal to 1-2 and/or with intrinsic luminosities larger than 3 x 10(44) ergs(-1) (2-10 keV at source frame).