Optical and Infrared Properties of the 2 Ms Chandra Deep Field North X-Ray Sources

Abstract

We present an optical and near-infrared catalog for the X-ray sources in the ?2 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 ? 24 sources is 87%. The spectroscopic redshift distribution shows two broad redshift spikes that have clearly grown over those originally seen in the ?1 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 5.7 that would classify them as extremely red objects (EROs). The photometric redshifts of these EROs are all between z ~ 1.5 and z ~ 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, 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.