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

Abstract

We present an optical and NIR catalog for the X-ray sources in the 2 Ms Chandra observation of the Hubble Deep Field-North region. We have high-quality multicolor images of all 503 X-ray point sources and reliable spectroscopic redshifts for 284. We spectroscopically identify six z>1 type II quasars. 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<1 and 68% from sources at z<2. We use seven broadband colors and a Bayesian photometric redshift estimation code to obtain photometric redshifts. The photometric redshifts are within 25% of the spectroscopic redshifts for 94% of the non-broad-line sources with both photometric and spectroscopic measurements. We use our wide wavelength coverage to determine rest-frame colors for the X-ray sources with spectroscopic or photometric redshifts. Many of the X-ray sources have the rest-frame colors of evolved red galaxies and 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 Mstar, even at high redshifts. We therefore infer that deep X-ray observations may provide an effective way of locating Mstar galaxies with colors similar to present-day early-type galaxies to high redshifts. (Abridged)