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For refcode 1995MNRAS.277....1S:
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Copyright by Royal Astronomical Society. 1995MNRAS.277....1S The discovery of two giant arcs in the rich cluster A2219 with the Keck telescope Ian Smail, David W. Hogg, Roger Blandford, Judith G. Cohen, Alastair C. Edge and S. George DjorgovsKi Palomar Observatory, Caltech 105-24, Pasadena, CA 91125, USA Theoretical Astrophysics, Caltech 130-33, Pasadena, CA 91125, USA Institute of Astronomy, Madingley Road Cambridge CB3 0HA Accepted 1995 May 11. Received 1995 April 27; in original form 1995 January 31 ABSTRACT We report the discovery with the Keck telescope of two new multiply imaged arcs in the luminous X-ray cluster A2219 (z = 0.225). The brighter arc in the field is red and we use spectroscopic and photometric information to identity it as a z ~ 1 moderately star-forming system. The brightness of this arc suggests that it is formed from two merging images of the background source, and we identity possible candidates for the third image of this source. The second giant arc in this cluster is blue and, while fainter than the red arc, it has a similarly large angular extent (32 arcsec). This arc comprises three images of a single nucleated source - the relative parities of the three images are discernible in our best-resolution images. The presence of several bright multiply imaged arcs in a single cluster allows detailed modelling of the cluster mass distribution, especially when redshift information is available. We present a lensing model of the cluster, which explains the properties of the various arcs, and we contrast this model with the optical and X-ray information available on the cluster. We uncover significant differences between the distributions of mass and X-ray gas in the cluster. We suggest that such discrepancies may indicate a on-going merger event in the cluster core, possibly associated with a group around the second brightest cluster member. The preponderance of similar merger signatures in a large fraction of the moderate-redshift clusters would indicate their dynamical immaturity. Key words: galaxies: clusters: individual: A2219 galaxies: evolution - galaxies: formation - galaxies: photometry - cosmology: observations - gravitational lensing.
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