Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996rftu.proc..649c&link_type=abstract
International Conference on X-ray Astronomy and Astrophysics: Röntgenstrahlung from the Universe, p. 649 - 650
Astronomy and Astrophysics
Astrophysics
X-Ray Surveys: Quasars, X-Ray Surveys: Galaxies, X-Ray Background, X-Ray Surveys: Stars, X-Ray Sources: Optical Identifications
Scientific paper
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.
Barber C. R.
Barcons Xavier
Burgos Juan Jacinto
Carballo Raúl
González-Serrano José Ignacio
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