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Published September 2007 | Published
Journal Article Open

A Wide-Angle Tail Radio Galaxy in the COSMOS Field: Evidence for Cluster Formation


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 HST ACS 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.

Additional Information

© 2007 American Astronomical Society. Print publication: Issue 1 (2007 September); received 2006 April 25; accepted for publication 2006 August 15. V. S. thanks Rachel Somerville and Klaus Meisenheimer for insightful discussions. C. C., E. S., and V. S. acknowledge support from NASA grant HST GO-09822.31-A; C. C. would like to acknowledge support from the Max Planck Society and the Alexander von Humboldt Foundation through the Max- Planck-Forschungspreis 2005. A. F. acknowledges support from BMBF/DLR under grant 50 OR 0207, MPG and a partial support from NASA grant NNG04GF686. I. S. acknowledges the support of the European Community under a Marie Curie Intra-European Fellowship. C. S. B. acknowledges funding by the Deutsche Forschungsgemeinschaft. K. J. acknowledges support by the German DFG under grant SCHI 536/3-1. The XMM-Newton project is an ESA Science Mission with instruments and contributions directly funded by ESA member states and the USA (NASA). The XMM-Newton project is supported by the Bundesministeriumfu¨rWirtschaft und Technologie/ Deutsches Zentrum fu¨r Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OX 0001), theMax Planck Society, and the Heidenhain- Stiftung, and also by PPARC, CEA, CNES, and ASI. Part of this work was also supported by the Deutsches Zentrum fu¨ r Luftund Raumfahrt, DLR project numbers 50 OR 0207 and 50 OR 0405. Funding for the Sloan Digital Sky Survey (SDSS) has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the US Department of Energy, the JapaneseMonbukagakusho, and theMax Planck Society. The SDSS Web site is http://www.sdss.org. The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are the University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, the Johns HopkinsUniversity, the Korean Scientist Group, Los AlamosNa- 2tional Laboratory, the Max Planck Institute for Astronomy, the Max Planck Institute for Astrophysics, New Mexico State University, theUniversity of Pittsburgh, theUniversity of Portsmouth, Princeton University, the US Naval Observatory, and the University of Washington.

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