The Chandra multiwavelength project: Optical follow-up of serendipitous Chandra sources

P. J. Green, J. D. Silverman, R. A. Cameron, D. W. Kim, B. J. Wilkes, W. A. Barkhouse, A. LaCluyzé, D. Morris, A. Mossman, H. Ghosh, J. P. Grimes, B. T. Jannuzi, H. Tananbaum, T. L. Aldcroft, J. A. Baldwin, F. H. Chaffee, A. Dey, A. Dosaj, N. R. Evans, X. FanC. Foltz, T. Gaetz, E. J. Hooper, V. L. Kashyap, S. Mathur, M. B. McGarry, E. Romero-Colmenero, M. G. Smith, P. S. Smith, R. C. Smith, G. Torres, A. Vikhlinin, D. R. Wik

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


We present follow-up optical g′, r′, and i′ imaging and spectroscopy of serendipitous X-ray sources detected in six archival Chandra images included in the Chandra Multiwavelength Project (ChaMP). Of the 486 X-ray sources detected between 3 × 10-16 and 2 × 10 -13 (with a median flux of 3 × 10-15) ergs cm -2 s-1, we find optical counterparts for 377 (78%), or 335 (68%) counting only unique counterparts. We present spectroscopic classifications for 125 objects, representing 75% of sources with r* < 21 optical counterparts (63% to r* = 22). Of all classified objects, 63 (50%) are broad-line active galactic nuclei (AGNs), which tend to be blue in (g*-r*) colors. X-ray information efficiently segregates these quasars from stars, which otherwise strongly overlap in these SDSS colors until z > 3.5. We identify 28 sources (22%) as galaxies that show narrow emission lines, while 22 (18%) are absorption line galaxies. Eight galaxies lacking broad-line emission have X-ray luminosities that require they host an AGN (log Lx > 43). Half of these have hard X-ray emission suggesting that high gas columns obscure both the X-ray continuum and the broad emission line regions. We find objects in our sample that show signs of X-ray or optical absorption, or both, but with no strong evidence that these properties are coupled. ChaMP's deep X-ray and optical imaging enable multiband selection of small and/or high-redshift groups and clusters. In these six fields we have discovered three new clusters of galaxies, two with z > 0.4, and one with photometric evidence for a similar redshift.

Original languageEnglish (US)
Pages (from-to)43-71
Number of pages29
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - Jan 2004


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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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