  The CDF-S is the deepest X-ray image available and will remain so for the
near future. We provide a spectroscopic (64.5%; 64% with spectral
classifications) and photometric redshift catalog for the full 7 Ms sample, but
much of our analysis focuses on the central (off-axis angles <5.7') region,
which contains a large, faint ALMA sample of 75 >4.5-sigma 850 micron sources.
We measure the 850 micron fluxes at the X-ray positions using the ALMA images,
where available, or an ultradeep SCUBA-2 map. We find that the full X-ray
sample produces ~10% of the 850 micron extragalactic background light. We
separate the submillimeter detected X-ray sources into star-forming galaxies
and AGNs using a star formation rate (SFR) versus X-ray luminosity calibration
for high SFR galaxies. We confirm this separation using the X-ray photon
indices. We measure the X-ray fluxes at the accurate positions of the 75 ALMA
sources and detect 70% at >3-sigma in either the 0.5-2 or 2-7 keV bands.
However, many of these may produce both their X-ray and submillimeter emission
by star formation. Indeed, we find that only 20% of the ALMA sources have
intermediate X-ray luminosities (rest-frame 8-28 keV luminosities of
10^42.5-10^44 erg/s), and none has a high X-ray luminosity (>10^44 erg/s).
Conversely, after combining the CDF-S with the CDF-N, we find extreme star
formation (SFR>300 solar masses per yr) in some intermediate X-ray luminosity
sources but not in any high X-ray luminosity sources. We argue that the
quenching of star formation in the most luminous AGNs may be a consequence of
the clearing of gas in these sources.
