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Published July 10, 2002 | Published + Accepted Version
Journal Article Open

Losing Weight: A Keck Spectroscopic Survey of the Massive Cluster of Galaxies RX J1347−1145


We present a sample of 47 spectroscopically confirmed members of RX J1347-1145, the most luminous X-ray cluster of galaxies discovered to date. With two exceptions, all the galaxies in this sample have red B-R colors and red spectral indices, with spectra similar to old local elliptical galaxies. Using all 47 cluster members, we derive a mean redshift of z = 0.4509 ± 0.003 and a velocity dispersion of 910 ± 130 km s^(-1), which corresponds to a virial mass of 4.4 × 10^(14) h^(-1) M☉ with a harmonic radius of 380 h^(-1) kpc. The derived total dynamical mass is marginally consistent with that deduced from the cluster's X-ray emission based on the analysis of ROSAT/ASCA images (Schindler and coworkers in 1997), but not consistent with the more recent X-ray analyses of Allen in 2000, Ettori, Allen, and Fabian in 2001, and Allen, Schmidt, and Fabian in 2002. Furthermore, the dynamical mass is significantly smaller than that derived from weak lensing (Fischer and Tyson in 1997) and from strong lensing (Sahu and coworkers in 1998). We propose that these various discrepant mass estimates may be understood if RX J1347-1145 is the product of two clusters caught in the act of merging in a direction perpendicular to the line of sight, although there is no evidence from the galaxy redshift distribution supporting this hypothesis. Even with this hypothesis, a significant part of the extremely high X-ray luminosity must still arise from nonvirialized, presumably shocked, gas. Finally, we report the serendipitous discovery of a lensed background galaxy at z = 4.083 that will put strong constraints on the lensing mass determination once its counterimage is securely identified.

Additional Information

© 2002 The American Astronomical Society. Received 2001 November 14; accepted 2002 March 12. Based in large part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and NASA. The entire Keck/LRIS user community owes a huge debt to Jerry Nelson, Gerry Smith, Bev Oke, and many other people who have worked to make the Keck Telescope and LRIS a reality. We are grateful to the W. M. Keck Foundation for the vision to fund the construction of the W. M. Keck Observatory. The authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible. The archival STIS data was retrieved from the STScI archive and was taken with the NASA/ESA Hubble Space Telescope, which is operated by STScI for the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. The archival Chandra/ACIS data was retrieved from the Chandra data archive, which is part of the Chandra X-Ray Science Center, operated for NASA by the Smithsonian Astrophysical Observatory. We are grateful to Oliver Czoske, Phil Fisher, and Piet van Dokkum for useful discussions and suggestions. J. P. K. thanks the CNRS for support.

Attached Files

Published - Cohen_2002_ApJ_573_524.pdf

Accepted Version - 0111294.pdf


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