The roadmap for unification in galaxy group selection. I. A search for extended x-ray emission in the CNOC2 survey

A. Finoguenov, J.L. Connelly, L.C. Parker, D.J. Wilman, J.S. Mulchaey, R.P. Saglia, M.L. Balogh, R.G. Bower, S.L. McGee

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53 Citations (Scopus)


X-ray properties of galaxy groups can unlock some of the most challenging research topics in modern extragalactic astronomy: the growth of structure and its influence on galaxy formation. Only with the advent of the Chandra and XMM-Newton facilities have X-ray observations reached the depths required to address these questions in a satisfactory manner. Here we present an X-ray imaging study of two patches from the CNOC2 spectroscopic galaxy survey using combined Chandra and XMM-Newton data. A state of the art extended source finding algorithm has been applied, and the resultant source catalog, including redshifts from a spectroscopic follow-up program, is presented. The total number of spectroscopically identified groups is 25 spanning a redshift range 0.04-0.79. Approximately 50% of CNOC2 spectroscopically selected groups in the deeper X-ray (RA14h) field are likely X-ray detections, compared to 20% in the shallower (RA21h) field. Statistical modeling shows that this is consistent with expectations, assuming an expected evolution of the LX -M relation. A significant detection of a stacked shear signal for both spectroscopic and X-ray groups indicates that both samples contain real groups of about the expected mass. We conclude that the current area and depth of X-ray and spectroscopic facilities provide a unique window of opportunity at z 0.4 to test the X-ray appearance of galaxy groups selected in various ways. There is at present no evidence that the correlation between X-ray luminosity and velocity dispersion evolves significantly with redshift, which implies that catalogs based on either method can be fairly compared and modeled. © 2009 The American Astronomical Society. All rights reserved.
Original languageEnglish
Pages (from-to)564-575
Number of pages12
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 2009


  • Catalogs
  • Cosmology: observations
  • Dark matter
  • Galaxies: clusters: general
  • Surveys
  • X-rays: galaxies: clusters


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