  With recent Chandra observations, at least 60% of the 2-10 keV background is
now resolved into discrete sources. Here we present deep optical, NIR, submm,
and 20 cm (radio) images, as well as high-quality optical spectra, of a
complete sample of 20 hard X-ray sources in a deep Chandra observation of the
SSA13 field. The thirteen I<23.5 galaxies have redshifts in the range 0.1 to
2.6. Two are quasars, five show AGN signatures, and six are z<1.5 luminous
bulge-dominated galaxies whose spectra show no obvious optical AGN signatures.
The seven spectroscopically unidentified sources have colors that are
consistent with evolved early galaxies at z=1.5-3. Only one hard X-ray source
is significantly detected in an ultradeep submm map; its millimetric redshift
is in the range z=1.2-2.4. None of the remaining 19 sources is detected in the
submm. These results probably reflect the fact that the 850-micron flux limits
obtainable with SCUBA are quite close to the expected fluxes from obscured AGN.
The hard X-ray sources have an average L(FIR)/L(2-10 keV)~60, similar to that
of local obscured AGN. The same ratio for a sample of submm selected sources is
in excess of 1100, suggesting that their FIR light is primarily produced by
star formation. Our data show that luminous hard X-ray sources are common in
bulge-dominated optically luminous galaxies. We use our measured bolometric
corrections with the 2-10 keV EBL to infer the growth of supermassive black
holes. Even with a high radiative efficiency of accretion (e=0.1), the black
hole mass density required to account for the observed light is comparable to
the local black hole mass density. (Abridged)
