Article

Chandra X-ray Observations of the 0.6 < z < 1.1 Red-Sequence Cluster Survey Sample

The Astrophysical Journal (Impact Factor: 6.28). 10/2007; 680(2). DOI: 10.1086/587682
Source: arXiv

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

Download full-text

Full-text

Available from: David Gilbank, Jan 11, 2013
0 Followers
 · 
124 Views
  • Source
    [Show abstract] [Hide abstract]
    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
    The Astrophysical Journal 08/2007; 671(2). DOI:10.1086/522879 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We use a statistical sample of similar to 500 rich clusters taken from 72 deg(2) of the Red-Sequence Cluster Survey (RCS-1) to study the evolution of similar to 30,000 red-sequence galaxies in clusters over the redshift range 0.35 < z < 0.95. We construct red-sequence luminosity functions (RSLFs) for a well-defined, homogeneously selected, richness-limited sample. The RSLF at higher redshifts shows a deficit of faint red galaxies (to M-V >= -19.7) with their numbers increasing toward the present epoch. This is consistent with the "downsizing" picture in which star formation ended at earlier times for the most massive (luminous) galaxies and more recently for less massive (fainter) galaxies. We observe a richness dependence to the downsizing effect in the sense that, at a given redshift, the drop-off of faint red galaxies is greater for poorer (less massive) clusters, suggesting that star formation ended earlier for galaxies in more massive clusters. The decrease in faint red-sequence galaxies is accompanied by an increase in faint blue galaxies, implying that the process responsible for this evolution of faint galaxies is the termination of star formation, possibly with little or no need for merging. At the bright end, we also see an increase in the number of blue galaxies with increasing redshift, suggesting that termination of star formation in higher mass galaxies may also be an important formation mechanism for higher mass ellipticals. By comparing with a low-redshift Abell cluster sample, we find that the downsizing trend seen within RCS-1 has continued to the local universe.
    The Astrophysical Journal 10/2007; 673(2). DOI:10.1086/524398 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We forecast the constraints on the values of sigma_8, Omega_m, and cluster scaling relation parameters which we expect to obtain from the XMM Cluster Survey (XCS). We assume a flat Lambda-CDM Universe and perform a Monte Carlo Markov Chain analysis of the evolution of the number density of galaxy clusters that takes into account a detailed simulated selection function. Comparing our current observed number of clusters shows good agreement with predictions. We determine the expected degradation of the constraints as a result of self-calibrating the luminosity-temperature relation (with scatter), including temperature measurement errors, and relying on photometric methods for the estimation of galaxy cluster redshifts. We examine the effects of systematic errors in scaling relation and measurement error assumptions. Using only (T,z) self-calibration, we expect to measure Omega_m to +-0.03 (and Omega_Lambda to the same accuracy assuming flatness), and sigma_8 to +-0.05, also constraining the normalization and slope of the luminosity-temperature relation to +-6 and +-13 per cent (at 1sigma) respectively in the process. Self-calibration fails to jointly constrain the scatter and redshift evolution of the luminosity-temperature relation significantly. Additional archival and/or follow-up data will improve on this. We do not expect measurement errors or imperfect knowledge of their distribution to degrade constraints significantly. Scaling-relation systematics can easily lead to cosmological constraints 2sigma or more away from the fiducial model. Our treatment is the first exact treatment to this level of detail, and introduces a new `smoothed ML' estimate of expected constraints.
    Monthly Notices of the Royal Astronomical Society 02/2008; 397(2). DOI:10.1111/j.1365-2966.2009.14923.x · 5.23 Impact Factor
Show more