A Multiwavelength Analysis of the Strong Lensing Cluster RCS 022434-0002.5 at z=0.778

The Astrophysical Journal (Impact Factor: 6.28). 08/2007; 671(2). DOI: 10.1086/522879
Source: arXiv

ABSTRACT We present the results of two (101 ks total) Chandra observations of the z=0.778 optically selected lensing cluster RCS022434-0002.5, along with weak lensing and dynamical analyses of this object. An X-ray spectrum extracted within R(2500) (362 h(70)^(-1) kpc) results in an integrated cluster temperature of 5.1 (+0.9,-0.5) keV. The surface brightness profile of RCS022434-0002.5 indicates the presence of a slight excess of emission in the core. A hardness ratio image of this object reveals that this central emission is primarily produced by soft X-rays. Further investigation yields a cluster cooling time of 3.3 times 10^9 years, which is less than half of the age of the universe at this redshift given the current LCDM cosmology. A weak lensing analysis is performed using HST images, and our weak lensing mass estimate is found to be in good agreement with the X-ray determined mass of the cluster. Spectroscopic analysis reveals that RCS022434-0002.5 has a velocity dispersion of 900 +/- 180 km/s, consistent with its X-ray temperature. The core gas mass fraction of RCS022434-0002.5 is, however, found to be three times lower than expected universal values. The radial distribution of X-ray point sources within R(200) of this cluster peaks at ~0.7 R(200), possibly indicating that the cluster potential is influencing AGN activity at that radius. Correlations between X-ray and radio (VLA) point source positions are also examined. Comment: 32 pages, 9 figures. Accepted for publication in The Astrophysical Journal

Download full-text


Available from: David Gilbank, Jan 11, 2013
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of Chandra observations of 13 optically-selected clusters with 0.6<z< 1.1, discovered via the Red-sequence Cluster Survey (RCS). All but one are detected at S/N>3; though 3 were not observed long enough to support detailed analysis. Surface brightness profiles are fit to beta-models. Integrated spectra are extracted within R(2500), and Tx and Lx information is obtained. We derive gas and total masses within R(2500) and R(500). Cosmologically corrected scaling relations are investigated, and we find the RCS clusters to be consistent with self-similar scaling expectations. However discrepancies exist between the RCS sample and lower-z X-ray selected samples for relationships involving Lx, with the higher-z RCS clusters having lower Lx for a given Tx. In addition, we find that gas mass fractions within R(2500) for the high-z RCS sample are lower than expected by a factor of ~2. This suggests that the central entropy of these high-z objects has been elevated by processes such as pre-heating, mergers, and/or AGN outbursts, that their gas is still infalling, or that they contain comparatively more baryonic matter in the form of stars. Finally, relationships between red-sequence optical richness (Bgc) and X-ray properties are fit to the data. For systems with measured Tx, we find that optical richness correlates with both Tx and mass, having a scatter of ~30% with mass for both X-ray and optically-selected clusters. However we also find that X-ray luminosity is not well correlated with richness, and that several of our sample appear to be significantly X-ray faint. Comment: 57 pages, 12 figures; submitted to The Astrophysical Journal. Figure quality reduced to comply with arXiv file size requirements
    The Astrophysical Journal 10/2007; 680(2). DOI:10.1086/587682 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Context: The study of the thermodynamical and chemical properties of the intra cluster medium (ICM) in high redshift clusters of galaxies is a powerful tool for investigating the formation and evolution of large scale structures. Here we discuss the X-ray properties of clusters of galaxies optically selected in the red-sequence cluster survey (RCS) observed with the Chandra satellite, at redshifts 0.6 < z < 1.2. Aims: We intend to assess the evolutionary stage of optically selected high-z clusters of galaxies, performing a spectral analysis of the diffuse emission from their ICM. We also investigate the distribution of active galactic nuclei (AGN) in their surroundings. Methods: The background subtracted spectra were analyzed and fitted with a single temperature model to measure average ICM temperature, X-ray bolometric luminosity and Fe abundance within typical radii between 200 and 350 kpc. We also analyzed the point source number density and spatial distribution in the RCS clusters fields as a function of the X-ray flux. Results: We detected emission for the majority of the clusters, except for three, for which we have only marginal detection at ˜ 3sigma. We find that the normalization of the luminosity-temperature relation for RCS clusters is a factor of ~2 lower than the one for X-ray selected clusters. We confirm that the Fe abundance in the detected objects is consistent with that of X-ray selected clusters at the same redshift. We also find an excess of low-luminosity AGN towards the center of the clusters. Conclusions: At z ~ 1, optically selected clusters with a well-defined red-sequence show extended X-ray emission in about 70% (8/11) of the cases. Nevertheless, their L_X-TX relation is significantly lower with respect to X-ray selected clusters at the same redshift, possibly indicating an incomplete virialization. The Fe abundance measured in the ICM of RCS clusters is comparable to the values measured for X-ray selected clusters at the same redshift, implying a substantial enrichment by SNe products. These two evidences add to the previously known studies of high-z, X-ray selected clusters, to confirm that the thermodynamical and chemical properties of the ICM are substantially established already at z > 1. Finally, we find the significant excess of medium and low luminosity AGN close to the centroid of the X-ray emission. Their X-ray emission is not dominating the ICM, but their presence may be relevant for studying the interaction between AGN and ICM.
    Astronomy and Astrophysics 10/2008; 489(3):967-979. DOI:10.1051/0004-6361:200809437 · 4.48 Impact Factor