1997•arXiv (Cornell University)Open access
The ROSAT Deep Survey II. Optical identification, photomettry and spectra of sources in the Lockman field
Maarten Schmidt, G. Hasinger, James E. Gunn, D. P. Schneider, R. Burg, R. Giacconi, I. Lehmann, John MacKenty, J. Truêmper, Zamorani, Gianni
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Abstract
The ROSAT Deep Survey includes a complete sample of 50 X-ray sources with fluxes in the $0.5 - 2$ keV band larger than 5.5 $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ in the Lockman field (Hasinger et al., Paper I). We have obtained deep broad-band CCD images of the field and spectra of many optical objects near the positions of the X-ray sources. We define systematically the process leading to the optical identifications of the X-ray sources. For this purpose, we introduce five identification (ID) classes that characterize the process in each case. Among the 50 X-ray sources, we identify 39 AGNs, 3 groups of galaxies, 1 galaxy and 3 galactic stars. Four X-ray sources remain unidentified so far; two of these objects may have an unusually large ratio of X-ray to optical flux. Keywords: surveys -- galaxies: active -- quasars: emission lines -- galaxies: Seyfert -- X-rays: galaxies
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