  We present the optical, near-infrared, submillimeter, and radio follow-up
catalog of the X-ray selected sources from the 1 Ms Chandra observation of the
Hubble Deep Field North region. We have B, V, R, I, and z' magnitudes for the
370 X-ray point sources, HK' magnitudes for 276, and spectroscopic redshifts
for 182. We present high-quality spectra for 175 of these. The redshift
distribution shows indications of structures at z=0.843 and z=1.0175 (also
detected in optical surveys) which could account for a part of the
field-to-field variation seen in the X-ray number counts. The flux
contributions separated into unit bins of redshift show that the z<1
spectroscopically identified sources already contribute about one-third of the
total flux in both the hard and soft bands. We find from ratios of the X-ray
counts that the X-ray spectra are well-described by absorption of an intrinsic
Gamma=1.8 power-law, with log NH values ranging from 21 to 23.7. We estimate
that the Chandra sources that produce 87% of the HEAO-A X-ray background (XRB)
at 3 keV produce 57% at 20 keV, provided that at high energies the spectral
shape of the sources continues to be well-described by a Gamma=1.8 power-law.
However, when the Chandra contributions are renormalized to the BeppoSAX XRB at
3 keV, the shape matches fairly well the observed XRB at both energies. Thus,
whether a substantial population of as-yet undetected Compton-thick sources is
required to completely resolve the XRB above 10 keV depends critically on how
the currently discrepant XRB measurements in the 1-10 keV energy range tie
together with the higher energy XRB. (Abridged)
