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

By A. Barger, L. Cowie, P. Capak, D. Alexander, F. E. Bauer, E. Fernandez, W. N. Brandt, G. Garmire, A. Hornschemeier. 2003

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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 < 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 ∼ 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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/41e55c72e894da2f96b6a41bb86210fa3fe685b6

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Citations in the corpus

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The HELLAS2XMM Survey. VII. The Hard X-Ray Luminosity Function of AGNs up to z = 4: More Absorbed AGNs at Low Luminosities and High Redshifts (2005, methodology): “We used both spectroscopic and spectrophotometric identifications and redshifts available from the literature (Barger et al. 2003).”
The Cosmic Evolution of Hard X-Ray-selected Active Galactic Nuclei (2004, methodology): “This is another statement that the lower luminosity sources peak in number at lower redshifts than the high-luminosity sources (e.g., Cowie et al. 2003; Hasinger 2003; Barger et al. 2003a; Steffen et al. 2003; Fiore et al. 2003; Ueda et al. 2003).”
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The Changing Active Galactic Nucleus Population (2003, methodology): “Although theoretical models of SMBH formation have relied on comparisons with the optical quasar luminosity function, optically accessible broad-line active galactic nuclei (AGNs) form only about 30% (Barger et al. 2003b) of the X-ray background (XRB).”
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