Optical and infrared properties of the 2 Ms Chandra Deep Field North X-ray sources

We present an optical and near-infrared catalog for the X-ray sources in the approximate to2 Ms Chandra observation of the Hubble Deep Field North region. We have high-quality multicolor imaging data for all 503 X-ray point sources in the X-ray-selected catalog and reliable spectroscopic redshifts for 284. We spectroscopically identify six high-redshift (z > 1) type II quasars (L2-8keV > 1044 ergs s(-1)) in our sample. Our spectroscopic completeness for the R less than or equal to 24 sources is 87%. The spectroscopic redshift distribution shows two broad redshift spikes that have clearly grown over those originally seen in the approximate to1 Ms exposure. The spectroscopically identified extragalactic sources already comprise 75% of the measured 2-8 keV light. Redshift slices versus 2-8 keV flux show that an impressive 54% of the measured 2-8 keV light arises from sources at z < 1 and 68% from sources at z < 2. Thus, major accretion onto supermassive black holes has occurred since the universe was half its present age. We use seven broadband colors and a Bayesian photometric redshift estimation code to obtain photometric redshifts for the X-ray sources. We find that the photometric redshifts are within 25% of the spectroscopic redshifts for 94% of the non-broad-line sources with both photometric and spectroscopic measurements. The photometrically identified sources show a smooth continuation of the spectroscopically identified sources to redder R-HK' color with increasing redshift, consistent with the galaxy tracks of evolved bulge-dominated galaxies. Fourteen have colors R-HK' > 5.7 that would classify them as extremely red objects (EROs). The photometric redshifts of these EROs are all between z similar to 1.5 and z similar to 2.5. We use our wide wavelength coverage to determine rest-frame colors for the X-ray sources with spectroscopic or photometric redshifts. We find that many of the X-ray sources have the rest-frame colors of evolved red galaxies and that there is very little evolution in these colors with redshift. We also determine absolute magnitudes and find that many of the non-broad-line sources are more luminous than M-I*, even at high redshifts. We therefore infer that deep X-ray observations may provide an effective way of locating M* galaxies with colors similar to present-day early-type galaxies to high redshifts.