Ma. Treyer et O. Lahav, FAINT BLUE GALAXIES AS A PROBE OF THE X-RAY-BACKGROUND AT HIGH-REDSHIFT, Monthly Notices of the Royal Astronomical Society, 280(2), 1996, pp. 469-480
We present a formalism describing the physical content of cross-correl
ation functions between a diffuse background and a population of discr
ete sources. The formalism is used to interpret cross-correlation sign
als between the unresolved X-ray background and a galaxy population re
solved to high redshift in another spectral band. Specifically, we app
ly it to the so-called faint blue galaxy population and constrain thei
r X-ray emissivity and clustering properties. A model is presented whi
ch satisfies the recently measured constraints on all three correlatio
n functions (galaxy/galaxy, background/background and galaxy/backgroun
d). This model predicts that faint galaxies in the magnitude range B =
18-23 (covering redshifts z less than or equal to 0.5) make up simila
r to 22 per cent of the X-ray background in the 0.5-2 keV band. At the
mean redshift of the galaxy sample, (z) over bar similar to 0.3, the
comoving volume emissivity is rho(X) similar to (6-9) x 10(38) h erg s
(-1) Mpc(-3). When extrapolated to fainter magnitudes, the faint blue
galaxy population can account for most of the residual background at s
oft X-ray energy. We show how the measurement of the angular and zero-
lag crosscorrelation functions between increasingly faint galaxies and
the X-ray background can in principle allow us to map the X-ray emiss
ivity as a function of redshift.