The ROSAT Deep Survey II. Optical identification, photomettry and spectra of sources in the Lockman field

/ Authors

M. Schmidt, G. Hasinger, J. Gunn, D. Schneider, R. Burg, R. Giacconi, I. Lehmann, J. Mackenty, J. Truemper, Gianni Zamorani Caltech

and 8 more authors

Astrophysikalisches Inst. Potsdam, P. University., P. S. University, J. University, Eso - Garching, StSCI Baltimore, Mpe Garching, Bologna Observatory

/ 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

Journal: arXiv: Astrophysics