The cluster RX J1347.521145, the most luminous cluster in the X-ray wavelengths, was imaged with the newly installed Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. 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° from the central galaxy. The STIS images also show approximately 100 faint galaxies within the radius of the arcs whose combined luminosity is ~4x10^11 L_. We also present ground-based spectroscopic observations of the northern arc that show one clear emission line at ~6730 A° , with a very faint continuum on either side. The emission line is consistent with an identification as [O ii] l3727, implying a redshift of 0.81 for this arc. The southern arc shows a faint continuum but no emission features. The surface mass within the radius of the arcs (240 kpc), as derived from the gravitational lensing, is ~6.3x10^14 M_. The resultant mass-to-light ratio of ~1200 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.). The total surface mass derived from the X-ray flux within the radius of the arcs is ~(2.1-6.8)x10^14 M_ , which implies that the ratio of the gravitational to the X-ray mass is ~1–3. The surface gas mass within this radius is ~3.5x10^13 M_, which implies that at least 6% of the total mass within this region is baryonic (Refer to PDF file for exact formulas).

Publication Date



Also archived in: arXiv: astro-ph/9709239 v2 4 Jan 1998 We would like to thank Mike Potter for assistance with the spectral data reduction. We thank Stella Seitz and Sabine Schindler for useful comments on the manuscript.ISSN:1538-4365 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

Document Type


Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus