obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555. RX J0848+4456: Disentangling a Moderate Redshift Cluster**Based on observations with the NASA/ESA Hubble Space Telescope (HST)

We present a multiwavelength study of RX J0848 + 4456, a cluster of galaxies discovered through X-ray emission in the ROSAT Deep Cluster Survey. Our observations consist of WFPC2 imaging, optical spectra, and X-ray data collected with the Chandra X-Ray Observatory. We find that RX J0848 + 4456 consists of an X-ray-emitting cluster of galaxies at a redshift of z = 0.570 and a group at a slightly lower redshift, z = 0.543, with little X-ray emission. This lower redshift system, however, is a gravitational lens, with the lensed galaxy being an unusual AGN or star-forming system at z = 3.356. The cluster has an X-ray temperature of kT = 3.6 0.4 keV, a bolometric luminosity of 1.0 0.3 1044 ergs s-1 and a velocity dispersion of 670 50 km s-1. These values all agree with the low-redshift correlations for clusters of galaxies, implying a relaxed system with the intracluster medium in equilibrium with the dark matter potential. The lower redshift group of galaxies at z = 0.543 has, at most, one-fifth, and more likely 1/10, of the X-ray luminosity of RX J0848 + 4456. Despite being a gravitational lens, this is a low-mass system, with an X-ray temperature of kT = 2.3+0.5-4 keV and a velocity dispersion of only 430 20 km s-1. Our observations show the importance of detailed studies of clusters of galaxies when using them as probes of cosmological mass functions.

Holden, B. P., Stanford, S. A., Rosati, P., Squires, G., Tozzi, P., Fosbury, R., ... Spinrad, H.

Holden, BP||Stanford, SA||Rosati, P||Squires, G||Tozzi, P||Fosbury, RAE||Papovich, C||Eisenhardt, P||Elston, R||Spinrad, H

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