The WARPS Survey - VIII. Evolution of the galaxy cluster X-ray Luminosity Function

L. A. Koens*, B. J. Maughan, L. R. Jones, H. Ebeling, D. J. Horner, E. S. Perlman, S. Phillipps, C. A. Scharf

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

5 Citations (Scopus)

Abstract

We present measurements of the galaxy cluster X-ray Luminosity Function (XLF) from the Wide Angle ROSAT Pointed Survey (WARPS) and quantify its evolution. WARPS is a serendipitous survey of the central region of ROSAT pointed observations and was carried out in two phases (WARPS-I and WARPS-II). The results here are based on a final sample of 124 clusters, complete above a flux limit of 6.5 x 10(-14) erg cm(-2) s(-1), with members out to redshift z similar to 1.05, and a sky coverage of 70.9 deg(2). We find significant evidence for negative evolution of the XLF, which complements the majority of X-ray cluster surveys. To quantify the suggested evolution, we perform a maximum likelihood analysis and conclude that the evolution is driven by a decreasing number density of high-luminosity clusters with redshift, while the bulk of the cluster population remains nearly unchanged out to redshift z approximate to 1.1, as expected in a low-density universe. The results are found to be insensitive to a variety of sources of systematic uncertainty that affect the measurement of the XLF and determination of the survey selection function. We perform a Bayesian analysis of the XLF to fully account for uncertainties in the local XLF on the measured evolution, and find that the detected evolution remains significant at the 95 per cent level. We observe a significant excess of clusters in the WARPS at 0.1 <z <0.3 and L-X approximate to 2 x 10(43) erg s(-1) compared with the reference low-redshift XLF, or our Bayesian fit to the WARPS data. We find that the excess cannot be explained by sample variance, or Eddington bias, and is unlikely to be due to problems with the survey selection function.

Original languageEnglish
Pages (from-to)3231-3242
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume435
Issue number4
DOIs
Publication statusPublished - Nov 2013

Keywords

  • galaxies: clusters: general
  • cosmology: observations
  • X-rays: galaxies: clusters
  • MEDIUM-SENSITIVITY SURVEY
  • ECLIPTIC POLE SURVEY
  • FLUX-LIMITED SAMPLE
  • DIGITAL SKY SURVEY
  • COSMOLOGICAL CONSTRAINTS
  • OBSERVED GROWTH
  • SOURCE CATALOG
  • PARAMETERS
  • VARIANCE
  • IV

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