The ROSAT UK medium sensitivity survey.
Abstract
The authors present the first results on the optical identification of 89 ROSAT sources on the second Lockman hole. Because of the low Galactic H I column density towards this region the X-ray spectra of the sources are relatively unaffected by Galactic absorption, and a relation between X-ray spectral properties and the nature of the sources can be established. The authors have been able to classify 51 of the sources (57%) as stars, optically extended galaxies or QSOs, on the basis of R-band CCD images, optical spectroscopy of the optically brightest sources, and colour information from APM measurements of the POSS plates. They find that the fraction of the X-ray sources in the sample identified with galaxies is ⪆10%. Similarly ⪆29% are QSOs and ≅10% are stars. The galaxies form a heterogeneous group of sources, including ellipticals without emission lines, normal star-forming, starburst and broad emission line galaxies. The X-ray spectra of the various types of galaxies are on average harder than those of the QSOs and more similar to the X-ray background (XRB). This suggests that galaxies may make a significant contribution to the soft X-ray source counts at faint flux levels and in the synthesis of the soft XRB.
- Publication:
-
Roentgenstrahlung from the Universe
- Pub Date:
- February 1996
- Bibcode:
- 1996rftu.proc..649C
- Keywords:
-
- X-Ray Surveys: Quasars;
- X-Ray Surveys: Galaxies;
- X-Ray Background;
- X-Ray Surveys: Stars;
- X-Ray Sources: Optical Identifications