ASCA Deep Survey in the Lockman Hole Field
Abstract
We present the results of deep observations of the Lockman Hole field with the ASCA SIS, covering 926 arcmin2 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 2-7keV bands, and only 4, 4, and 1 sources remain unidentified, respectively. The average hardness of the sources detected in the 1-7keV band with fluxes of between 10-14 and 10-13erg cm -2 s-1 corresponds to a photon index of 1.65 +/- 0.10. Type-2 AGNs show significantly harder spectra than type-1s, which can be explained by absorption column densities of NH simeq 1022-23 cm-2 at the source redshifts. Fifteen sources are detected in the hard-band (2-7keV), 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 2-7keV band at a flux level of 3 × 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 NH < 1023 cm-2 , in the redshift range z gtsim 1-2 and/or with intrinsic luminosities larger than 3 × 1044erg s-1 (2-10keV at source frame).
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- June 2001
- DOI:
- 10.1093/pasj/53.3.445
- Bibcode:
- 2001PASJ...53..445I
- Keywords:
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- GALAXIES: ACTIVE;
- SURVEYS;
- X-RAYS: GALAXIES;
- X-RAYS: GENERAL