We present the optical , near-infrared , submillimeter , and radio follow-up catalog of the X-ray selected sources from an \approx 1 Ms Chandra observation of the Hubble Deep Field North region .
We have B , V , R , I , and z ^ { \prime } magnitudes for the 370 X-ray point sources , HK ^ { \prime } 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 ; however , these structures do not dominate the number of X-ray sources in the sample and hence should not strongly affect the redshift distribution .
All of the X-ray sources with z > 1.6 are either broad-line AGN or have narrow Ly \alpha and/or CIII ] 1909 Å emission ; none of the known z > 1.6 absorption-line galaxies in the field are detected individually in X-rays .
We estimate photometric redshifts for the sources with B - I > 1.5 ( bluer than this it is hard to distinguish between low redshift irregulars and luminous high-redshift AGN ) and find agreement ( most are within 25 % ) with the available spectroscopic redshifts .
The majority of the galaxies in both the 2 - 8 keV ( hard ) and 0.5 - 2 keV ( soft ) samples have absolute magnitudes comparable to or more luminous than M _ { I } ^ { \ast } = -22 .
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 .
Thus , major accretion onto supermassive black holes has occurred since the Universe was half its present age .
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 N _ { H } values ranging from about 10 ^ { 21 } cm ^ { -2 } to 5 \times 10 ^ { 23 } cm ^ { -2 } .
We find very little evolution in the maximum rest-frame opacity-corrected and K -corrected 2 - 8 keV X-ray luminosities with decreasing redshift until z \lesssim 0.5 , where the volume becomes too small to probe effectively very high luminosity sources .
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 , or some change in the spectral shape of the current sources from the simple power-law dependence , 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 .