Large-scale structure of the universe - constraints from the X-ray background

The HEAO-1 limits on the intensity fluctuations of the hard X-ray background are used to impose limits on the large-scale structure of the universe at large redshifts. It is found that if the present-day structures are extrapolated backward maintaining an approximately constant physical separation between structures, then either the universe is much less structured at z greater than 0.5 or else the sources of the X-ray background do not follow the matter distribution. Alternatively, if the present-day structures are extrapolated backward maintaining an approximately constant comoving separation between structures, then the sources of the X-ray background may follow the matter clustering beyond z greater than 0.5. In this case, for Omega(0) less than 1, the fluctuations due to clustering are less than the observed upper limit, but for Omega(0) = 1 they produce fluctuations close to this upper limit. 20 references