  We identify a deep sample of 198 extremely red objects (EROs) in (50.4 sq.
arcmin of) the Chandra Deep Field South, selected as I-K>3.92 galaxies to a
limit K=22. The ERO number counts remain well below the predictions for pure
luminosity evolution, and fall below even a non-evolving model, suggesting the
comoving number density of passive/very red galaxies decreases with redshift.
The angular correlation function of these EROs indicates stronger clustering
than that of other galaxies at the same magnitudes, and is best-fitted by
models in which the EROs have a comoving correlation radius 12.5/h Mpc, or
21.4/h Mpc in a stable clustering model. We find a 40-arcsec diameter grouping
of 10 EROs, centered on the Chandra source (and ERO) XID:58, with colours
suggesting a cluster of mostly passive EROs at approx. z=1.5. The 942 ksec
Chandra survey detected 73 X-ray sources in the area of our ERO sample, of
which 17 coincide with EROs. Of these sources, 13 have X-ray properties
indicative of obscured AGN, while the faintest 4 may be starburst galaxies. In
addition, we find evidence that Chandra sources and EROs are positively
cross-correlated at non-zero (2-20 arcsec) separations, implying that they tend
to trace the same large-scale structures.
