Bibcode
Carballo, R.; Warwick, R. S.; Barcons, X.; González-Serrano, J. I.; Barber, C. R.; Pérez-Fournon, I.; Martínez-González, E.; Burgos, J.
Referencia bibliográfica
International Conference on X-ray Astronomy and Astrophysics: Röntgenstrahlung from the Universe, p. 649 - 650
Fecha de publicación:
2
1996
Número de citas
0
Número de citas referidas
0
Descripción
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.