Chandra centres for COSMOS X-ray galaxy groups: Differences in stellar properties between central dominant and offset brightest group galaxies

Ghassem Gozaliasl, Alexis Finoguenov, Masayuki Tanaka, Klaus Dolag, Francesco Montanari, Charles C. Kirkpatrick, Eleni Vardoulaki, Habib G. Khosroshahi, Mara Salvato, Clotilde Laigle, Henry J. McCracken, Olivier Ilbert, Nico Cappelluti, Emanuele Daddi, Guenther Hasinger, Peter Capak, Nick Z. Scoville, Sune Toft, Francesca Civano, Richard E. GriffithsMichael Balogh, Yanxia Li, Jussi Ahoranta, Simona Mei, Angela Iovino, Bruno M.B. Henriques, Ghazaleh Erfanianfar

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


We present the results of a search for galaxy clusters and groups in the ∼2 deg2 of the COSMOS field using all available X-ray observations from the XMM-Newton and Chandra observatories. We reach an X-ray flux limit of 3 × 10-16 erg cm-2 s-1 in the 0.5-2 keV range, and identify 247 X-ray groups with M200c = 8 × 1012-3 × 1014 M· at a redshift range of 0.08 = z < 1.53, using the multiband photometric redshift and the master spectroscopic redshift catalogues of the COSMOS. The X-ray centres of groups are determined using high-resolution Chandra imaging. We investigate the relations between the offset of the brightest group galaxies (BGGs) from halo X-ray centre and group properties and compare with predictions from semi-analytic models and hydrodynamical simulations. We find that BGG offset decreases with both increasing halo mass and decreasing redshift with no strong dependence on the X-ray flux and SNR. We show that the BGG offset decreases as a function of increasing magnitude gap with no considerable redshift-dependent trend. The stellar mass of BGGs in observations extends over a wider dynamic range compared to model predictions. At z < 0.5, the central dominant BGGs become more massive than those with large offsets by up to 0.3 dex, in agreement with model prediction. The observed and predicted log-normal scatter in the stellar mass of both low-and large-offset BGGs at fixed halo mass is ∼0.3 dex.

Original languageEnglish (US)
Pages (from-to)3545-3565
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Mar 1 2019


  • Galaxies: clusters: general
  • Galaxies: evolution
  • Galaxies: groups: general
  • Galaxies: statistics
  • Galaxies: stellar content
  • X-rays: galaxies: clusters

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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