The Chandra XBoötes survey. III. Optical and near-infrared counterparts

Kate Brand, Michael J.I. Brown, Arjun Dey, Buell T. Jannuzi, Christopher S. Kochanek, Almus T. Kenter, Daniel Fabricant, Giovanni G. Fazio, William R. Forman, Paul J. Green, Christine J. Jones, Brian R. McNamara, Stephen S. Murray, Joan R. Najita, Marcia Rieke, Joseph C. Shields, Alexey Vikhlinin

Research output: Contribution to journalArticlepeer-review

59 Scopus citations


The XBoötes Survey is a 5 ks Chandra survey of the Boötes Field of the NOAO Deep Wide-Field Survey (NDWFS). This survey is unique in that it is the largest (9.3 deg2) contiguous region imaged in X-ray with complementary deep optical and near-infrared (near-IR) observations. We present a catalog of the optical counterparts to the 3213 X-ray point sources detected in the XBoötes survey. Using a Bayesian identification scheme, we successfully identified optical counterparts for 98% of the X-ray point sources. The optical colors suggest that the optically detected galaxies are a combination of z < 1 massive early-type galaxies and bluer star-forming galaxies whose optical AGN emission is faint or obscured, whereas the majority of the optically detected point sources are likely quasars over a large redshift range. Our large-area, X-ray-bright, optically deep survey enables us to select a large sub-sample of sources (773) with high X-ray-to-optical flux ratios (fx/fo > 10). These objects are likely high-redshift and/or dust-obscured AGNs. These sources have generally harder X-ray spectra than sources with 0.1 < fx/fo < 10. Of the 73 X-ray sources with no optical counterpart in the NDWFS catalog, 47 are truly optically blank down to R ∼ 25.5 (the average 50% completeness limit of the NDWFS R-band catalogs). These sources are also likely to be high-redshift and/or dust-obscured AGNs.

Original languageEnglish (US)
Pages (from-to)140-157
Number of pages18
JournalAstrophysical Journal
Issue number1 I
StatePublished - Apr 10 2006


  • Galaxies: active
  • Surveys
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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