Imaging and spectroscopy of arcs around the most luminous X-ray cluster RXJ 1347 . 5-1145 1

The cluster RXJ 1347.5-1145, the most luminous cluster in the X-ray wavelengths, was imaged with the newly installed Space Telescope Imaging Spectrograph (STIS) on-board HST. Its relatively high redshift (0.451) and luminosity indicate that this is one of the most massive of all known clusters. The STIS images unambiguously show several arcs in the cluster. The largest two arcs (>5 length) are symmetrically situated on opposite sides of the cluster, at a distance of ∼ 35 arcsec from the central galaxy. The STIS images also show approximately 100 faint galaxies within the radius of the arcs whose combined luminosity is ∼ 4 × 10L⊙. We also present ground-based spectroscopic observations of the northern arc which show one clear emission line at ∼6730 Å, with a very faint continuum on either side. The emission line is consistent with an identification as [OII] 3727 Å, implying a redshift of 0.81 for this arc. The southern arc shows a faint continuum but no emission features. The mass of the lensing cluster, as derived from the gravitational lensing, is ∼4.2 × 10 M⊙. The resultant mass-to-light ratio of ∼ 1000 is higher than what is seen in many clusters but smaller than the value recently derived for some ‘dark’ X-ray clusters (Hattori et al. 1997). The mass derived from the X-ray flux within the radius of the arcs (240 kpc) is ∼1.3 × 10 M⊙. The ratio of the gravitational to the X-ray mass is ∼3 which, within the uncertainties, is consistent with the value derived for the whole cluster by Fischer and Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc under NASA contract NAS5-26555, and the 3.6-meter telescope of the European Southern Observatory at La Silla, Chile. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 NASA/Goddard Space Flight Center, Code 681, Greenbelt, MD 20771 Hughes/STX Corporation NASA/Goddard Space Flight Center, Code 681, Greenbelt, MD 20771 Dominion Astrophyscial Observatory, National Research Council of Canada, 5071 Saanich Rd., Victoria, B.C. V8X 4M6, Canada Dept of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 Advanced Computer Concepts, NASA/GSFC, Code 681, Greenbelt, MD 20771