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For refcode 1997MNRAS.285..511B:
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Copyright by Royal Astronomical Society. 1997MNRAS.285..511B The Cambridge-Cambridge ROSAT Serendipity Survey - V. Catalogue and optical identifications B. J. Boyle, B. J. Wilkes and M. Elvis Accepted 1996 September 18. Received 1996 July 31; in original form 1996 April 9 ABSTRACT We report the results of a medium-depth X-ray survey of 20 ROSAT Position Sensitive Proportional Counter (PSPC) fields. 123 X-ray sources were detected down to a flux limit of S(0.5-2 keV) > 2 x 10^-14^ erg s^-1^ cm^-2^ lying between that of the Einstein Extended Medium Sensitivity Survey (EMSS) and the deepest ROSAT surveys. Optical identifications of 110 of these sources have revealed 68 QSOs, 12 narrow-emission-line X- ray-luminous galaxies (NLXGs), 24 stars, two BL Lac objects, two galaxies and two clusters. CCD imaging reveals the possible presence of galaxy groups or clusters at the positions of a further four X-ray sources. The number-redshift and log N-log S relations of the 68 QSOs are in better agreement with the faster rate of cosmological evolution for X-ray QSOs derived from ROSAT deep surveys [L_x_ is proportional to (1 + z)^3.34+/- 0.01^, Z_max_ = 1.79] than with the evolution obtained from the EMSS [L_x_ is proportional to (1+z)^2.55+/-0.1^], the latter being rejected at greater than the 3{sigma} level as a model for the current sample. We present the optical spectra and measurements of the emission lines. The equivalent-width distributions are consistent with those of QSO samples selected in other wavebands. We find no evidence for an inverse correlation between line width and X-ray spectral slope as recently reported for other ROSAT QSO samples. Key words: surveys - galaxies: active - quasars: general - X-rays: general.
Retrieve 151 NED objects in this reference.
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