Figure 4. I-band magnitude versus
0.5-2 keV flux for extragalactic X-ray
sources in the CDF-N (triangles) and CDF-S (squares).
Sources with redshifts of 0-0.5, 0.5-1,
1-2, and 2-6 are shown as violet, blue, green, and red
symbols, respectively (symbol sizes also increase with redshift).
Small black dots indicate sources without spectroscopic redshifts. The
slanted, dotted lines indicate constant values of
log(fX / fI); the respective
log(fX / fI) values are
labeled. Note the broad range of
optical magnitudes at faint X-ray fluxes and that a large fraction of
the optically faint X-ray sources lack spectroscopic redshifts. |