A wide-angle tail radio galaxy in the COSMOS field: Evidence for cluster formation

V. Smolčić, E. Schinnerer, A. Finoguenov, I. Sakelliou, C. L. Carilli, C. S. Botzler, M. Brusa, N. Scoville, M. Ajiki, P. Capak, L. Guzzo, G. Hasinger, C. Impey, K. Jahnke, J. S. Kartaltepe, H. J. McCracken, B. Mobasher, T. Murayama, S. S. Sasaki, Y. ShioyaY. Taniguchi, J. R. Trump

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


We have identified a complex galaxy cluster system in the COSMOS field via a wide-angle tail (WAT) radio galaxy, consistent with the idea that WAT galaxies can be used as tracers of clusters. The WAT galaxy, CWAT-01, is coincident with an elliptical galaxy resolved in the HSTACS image. Using the COSMOS multiwavelength data set, we derive the radio properties of CWAT-01 and use the optical and X-ray data to investigate its host environment. The cluster hosting CWAT-01 is part of a larger assembly consisting of a minimum of four X-ray luminous clusters within ∼2 Mpc distance. We apply hydrodynamic models that combine ram pressure and buoyancy forces on CWAT-01. These models explain the shape of the radio jets only if the galaxy's velocity relative to the intracluster medium (ICM) is in the range of about 300-550 km s-1, which is higher than expected for brightest cluster galaxies (BCGs) in relaxed systems. This indicates that the CWAT-01 host cluster is not relaxed but is possibly dynamically young. We argue that such a velocity could have been induced through subcluster merger within the CWAT-01 parent cluster and/or cluster-cluster interactions. Our results strongly indicate that we are witnessing the formation of a large cluster from an assembly of multiple clusters, consistent with the hierarchical scenario of structure formation. We estimate the total mass of the final cluster to be approximately 20% of the mass of the Coma Cluster.

Original languageEnglish (US)
Pages (from-to)295-313
Number of pages19
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - 2007


  • Cosmology: observations
  • Galaxies: individual (CWAT-01)
  • Galaxies: jets
  • Radio continuum: galaxies
  • Surveys
  • X-rays: galaxies: clusters

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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