X-rays from quasars, resolved and
diffuse background recorded by ROSAT
An ultradeep ROSAT image (200 ks PSPC and 1000 ks HRI exposure times)
in the direction of the Lockman Hole, where the interstellar absorption
has an absolute minimum, provides the most sensitive X-ray observation
Intensive optical follow-up spectroscopy is carried out with
the Keck telescopes to reveal the nature of the X-ray faintest objects
discovered so far. These observations are relevant to determine the
cosmological evolution of galaxies with different stages of activity
and to reveal the nature of the enigmatic X-ray background radiation.
More than 70% of the 1-2 keV X-ray background has now been resolved
into discrete sources, the majority of which are active galaxies,
presumably with a central black hole.
The diagram shows the ROSAT log N - log S distribution
(source counts as a function of flux) which clearly reveals a deviation from
an Euclidean behaviour, a direct evidence for the strong cosmologic evolution
of the X-ray source population.
Hasinger, G., R. Burg, R. Giacconi, G. Hartner, M. Schmidt, J. Trümper,
A deep X-ray survey in the Lockman-hole and the soft X-ray
log N - log S,
Astron. & Astrophys. 275, 1-15 (1993)
from ADS service.
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© X-Ray Group at MPE (group)
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