Ksub(α) lines in the X ray background spectrum and interstellar gas in galaxies

Atoms and ions of heavy elements in interstellar space absorb X-ray background radiation and radiate Kα-lines photons. Therefore Kα-lines of iron, sulphur and silicon must be observed in the X-ray background spectrum in the direction to the plane of the galaxy. Their intensities are estimated. Observation of these lines permits to obtain additional information about the mass and spatial distribution of the interstellar gas. The X-ray radiation of the powerful X-ray source in the nucleus of a galaxy must be scattered and transformed into Kα-lines by the interstellar gas in the galaxy around nucleus. Observations of the diffuse X-Ray radiation of the external galaxies in continuum and Kα-lines permit to study the distribution of the interstellar gas inside them and to find the temporal variability of the central source X-Ray liminosity