The ROSAT-ESO Flux-Limited X-Ray (REFLEX) galaxy cluster survey

We present a measure of the power spectrum on scales from 15 to using the ROSAT-ESO Flux-Limited X-Ray (REFLEX) galaxy cluster catalogue. The REFLEX survey provides a sample of the 452 X-ray brightest southern clusters of galaxies with the nominal flux limit for the ROSAT energy band keV. Several tests are performed showing no significant incompletenesses of the REFLEX clusters with X-ray luminosities brighter than up to scales of about . They also indicate that cosmic variance might be more important than previous studies suggest. We regard this as a warning not to draw general cosmological conclusions from cluster samples with a size smaller than REFLEX. Power spectra, , of comoving cluster number densities are estimated for flux- and volume-limited subsamples. The most important result is the detection of a broad maximum within the comoving wavenumber range . The data suggest an increase of the power spectral amplitude with X-ray luminosity. Compared to optically selected cluster samples the REFLEX is flatter for wavenumbers thus shifting the maximum of to larger scales. The smooth maximum is not consistent with the narrow peak detected at using the Abell/ACO richness ≥0 data. In the range general agreement is found between the slope of the REFLEX and those obtained with optically selected galaxies. A semi-analytic description of the biased nonlinear power spectrum in redshift space gives the best agreement for low-density Cold Dark Matter models with or without a cosmological constant.