The WARPS Survey. III. The Discovery of an X‐Ray Luminous Galaxy Cluster atz = 0.833 and the Impact of X‐Ray Substructure on Cluster Abundance Measurements

Abstract

The WARPS (Wide Angle ROSAT Pointed Survey) team reviews the properties and history of discovery of ClJ0152.7-1357, an X-ray luminous, rich cluster of galaxies at a redshift of z = 0.833. At L X = 8 × 10 44 h −2 50 erg s −1 (0.5 − 2.0 keV) ClJ0152.7-1357 is the most X-ray luminous cluster known at redshifts z > 0.55. The high X-ray luminosity of the system suggests that massive clusters may begin to form at redshifts considerably greater than unity. This scenario is supported by the high degree of optical and X-ray substructure in ClJ0152.7-1357, which is similarly complex as that of other X-ray selected clusters at comparable redshift and consistent with the hypothesized picture of cluster formation by mass infall along large-scale filaments.X-ray emission from ClJ0152.7-1357 was detected already in 1980 with the EINSTEIN IPC. However, because the complex morphology of the emission caused its significance to be underestimated, the corresponding source was not included in the cluster sample of the EINSTEIN Extended Medium Sensitivity Survey (EMSS) and hence not previously identified. Simulations of the EMSS source detection and selection procedure performed by us suggest a general, mild bias of the EMSS cluster sample against X-ray luminous clusters with pronounced substructure.If highly unrelaxed, merging clusters are common at intermediate to high redshift (as is suggested by the current data) they could create a bias in some samples as the morphological complexity of mergers may cause them to fall below the flux limit of surveys that make the implicit or explicit assumption of a unimodal spatial source geometry. Conversely, the enhanced X-ray luminosity of mergers might cause them to, temporarily, rise above the flux limit. Either effect could lead to erroneous conclusions about the evolution of the comoving cluster space density. A high fraction of morphologically complex clusters at high redshift would also call into question the validity of evolutionary studies (and, specifically, cosmological conclusions) which implicitly or explicitly assume that the systems under investigation are virialized.

An X-ray review of MS 1054–0321: Hot or not?

“…The iron abundance inferred from the XMM-Newton observations is found to be in very good agreement with previous determinations by both J01 (Z = 0.38±0.15 Z ) and by Tozzi et al (2003) (Z = 0.35 ± 0.07 Z ) after their abundances are rescaled to the Grevesse & Sauval (1998) values while Vikhlinin et al (2002) fix the abundance to Z = 0.3 Z . MS 1054−0321 is in many aspects very similar to other distant X-ray selected clusters like RX J1717+67 at z = 0.81 (Gioia et al 1999), or RX J0152.7−1357 at z = 0.83 (Della Ceca et al 2000;Ebeling et al 2000) which show elongated or double morphologies in optical, weak lensing and X-rays and which have moderate temperature values.…”

PACS Evolutionary Probe (PEP) – AHerschelkey program

“…For redshifts around 1, our blank field observations sample a range of environments from the field to moderately massive clusters, which are known in particular in COSMOS due to its large angular size but still excellent multiwavelength characterization. To extend this to the full range of environments at this redshift, we add dedicated observations of two of the beststudied massive z ∼ 1 clusters, RXJ0152.7-1357 (e.g., Ebeling et al 2000) and MS1054.4-0321 (e.g., Tran et al 1999). We use the amplification provided by massive galaxy clusters to study sources that would otherwise be too faint for direct observations even in our deepest blank fields, and to provide highest quality SEDs on more luminous objects that are also detectable in the blank fields.…”

A Serendipitous Galaxy Cluster Survey withXMM: Expected Catalog Properties and Scientific Applications

“…Clusters in the process of formation may have signiÐcant nonthermal components to their X-ray luminosities, for example, from shocks resulting from subcluster merging. A classic example of such a cluster is RX J0152.7 (Ebeling et al 2000 ;Romer et al 2000), which has a high total luminosity (8.26 ] 1044 ergs s~1, z \ 0.83) but is made up of at least two components. It is not possible to predict, at this stage, what the net e †ect of unvirialized systems will be on the properties of the XCS, but the spatial and spectral resolution of EPIC should help us to recognize such systems.…”