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Register a new userThe X-ray Luminosity - Velocity Dispersion relation in the REFLEX Cluster Survey
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We present an estimate of the bolometric X-ray luminosity - velocity dispersion L_x - sigma_v relation measured from a new, large and homogeneous sample of 171 low redshift, X-ray selected galaxy clusters. The linear fitting of log(L_x) - log(sigma_v) gives L_x = 10^{32.72 pm 0.08} sigma^{4.1 pm 0.3}_v erg s^{-1} h^{-2}_{50}. Furthermore, a study of 54 clusters, for which the X-ray temperature of the intracluster medium T is available, allows us to explore two other scaling relations, L_x -T and sigma_v -T. From this sample we obtain L_x propto T^{3.1 pm 0.2} and sigma_v propto T^{1.00 pm 0.16}, which are fully consistent with the above result for the L_x-sigma_v. The slopes of L_x -T and sigma_v -T are incompatible with the values predicted by self-similarity (L_x propto T^{2} propto sigma_v^4), thus suggesting the presence of non-gravitational energy sources heating up the intracluster medium, in addition to the gravitational collapse, in the early stages of cluster formation. On the other hand, the result on log(L_x) - log(sigma_v) supports the self-similar model.
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The X-ray galaxy cluster sample from the REFLEX Cluster Survey, which covers the X-ray brightest galaxy clusters detected in the ROSAT All-Sky Survey in the southern sky, is used to construct the X-ray luminosity function of clusters in the local Universe. With 452 clusters detected above an X-ray flux-limit of 3 10^(-12) erg s^(-1) cm^(-2) in 4.24 sr of the sky, this sample is the most comprehensive X-ray cluster sample with a well documented selection function, providing the best current census of the local X-ray galaxy cluster population. In this paper we discuss the construction of the luminosity function, the effects of flux measurement errors and of variations with sample region and we compare the results to those from previous surveys.
We present the catalogue of the REFLEX Cluster Survey providing information on the X-ray properties, redshifts, and some identification details of the clusters in the REFLEX sample. The catalogue describes a statistically complete X-ray flux-limited sample of 447 galaxy clusters above an X-ray flux of 3 10(-12) erg /s/cm**2 (0.1 to 2.4 keV) in an area of 4.24 ster in the southern sky. The cluster candidates were first selected by their X-ray emission in the ROSAT-All Sky Survey and subsequently spectroscopically identified in the frame of an ESO key programme. In addition to the cluster catalogue we also describe the complete selection criteria as a function of the sky position and the conversion functions used to analyse the X-ray data. These are essential for the precise statistical analysis of the large-scale cluster distribution. This data set is at present the largest, statistically complete X-ray galaxy cluster sample. Together with these data set we also provide for the first time the full three-dimensional selection function. The sample forms the basis of several cosmological studies, one of the most important applications being the assessment of the statistics of the large-scale structure of the universe and the test of cosmological models.
We present a catalogue of X-ray selected galaxy clusters and groups as a first release of the 2XMMi/SDSS Galaxy Cluster Survey. The survey is a search for galaxy clusters detected serendipitously in observations with XMM-Newton in the footprint of the Sloan Digital Sky Survey (SDSS). The main aims of the survey are to identify new X-ray galaxy clusters, investigate their X-ray scaling relations, identify distant cluster candidates and study the correlation of the X-ray and optical properties. In this paper we describe the basic strategy to identify and characterize the X-ray cluster candidates that currently comprise 1180 objects selected from the second XMM-Newton serendipitous source catalogue (2XMMi-DR3). Cross-correlation of the initial catalogue with recently published optically selected SDSS galaxy cluster catalogues yields photometric redshifts for 275 objects. Of these, 182 clusters have at least one member with a spectroscopic redshift from existing public data (SDSS-DR8). Here we present the X-ray properties of the first cluster sample which comprises 175 clusters, among which 139 objects are new X-ray discoveries while the others were previously known as X-ray sources. The first cluster sample from the survey covers a wide range of redshifts from 0.09 to 0.61, bolometric luminosities L_500 = 1.9 x 10^42 - 1.2 x 10^45 erg/s, and masses M_500 = 2.3 x 10^13 - 4.9 x 10^14 Msun. We extend the relation between the X-ray bolometric luminosity L_500 and the X-ray temperature towards significantly lower T and L and still find that the slope of the linear L-T relation is consistent with values published for high luminosities.
We introduce a new test to study the Cosmological Principle with galaxy clusters. Galaxy clusters exhibit a tight correlation between the luminosity and temperature of the X-ray-emitting intracluster medium. While the luminosity measurement depends on cosmological parameters through the luminosity distance, the temperature determination is cosmology-independent. We exploit this property to test the isotropy of the luminosity distance over the full extragalactic sky, through the normalization $a$ of the $L_X-T$ scaling relation and the cosmological parameters $Omega_m$ and $H_0$. We use two almost independent galaxy cluster samples: the ASCA Cluster Catalog (ACC) and the XMM Cluster Survey (XCS-DR1). Interestingly enough, these two samples appear to have the same pattern for $a$ with respect to the Galactic longitude. We also identify one sky region within $lsim (-15^o,90^o)$ (Group A) that shares very different best-fit values for $a$ for both samples. We find the deviation of Group A to be $2.7sigma$ for ACC and $3.1sigma$ for XCS-DR1. This tension is not relieved after excluding possible outliers or after a redshift conversion to the CMB frame is applied. Using also the HIFLUGCS sample, we show that a possible excess of cool-core clusters in this region, cannot explain the obtained deviations. Moreover, we tested for a dependence of the $L_X-T$ relation on supercluster environment. We indeed find a trend for supercluster members to be underluminous compared to field clusters. However, the fraction of supercluster members is similar in the different sky regions. Constraining $Omega_m$ and $H_0$ via the redshift evolution of $L_X-T$ and the luminosity distance, we obtain approximately the same deviation amplitudes as for $a$. The observed behavior of $Omega_m$ for the sky regions that coincide with the CMB dipole is similar to what was found with other cosmological probes as well.
We present a measure of the power spectrum on scales from 15 to 800 Mpc/h 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 S=3.0 10^{-12}erg/s/cm2 for the ROSAT energy band (0.1-2.4)keV. Several tests are performed showing no significant incompletenesses of the REFLEX clusters with X-ray luminosities brighter than 10^{43}erg/s up to scales of about 800 Mpc/h. 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, P(k), 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 0.022<k<0.030 h/Mpc. The data suggest an increase of the power spectral amplitude with X-ray luminosity. Compared to optically selected cluster samples the REFLEX P(k)is flatter for wavenumbers k<0.05 h/Mpc thus shifting the maximum of P(k) to larger scales. The smooth maximum is not consistent with the narrow peak detected at k=0.05 h/Mpc using the Abell/ACO richness $ge 0$ data. In the range 0.02<k<0.4 h/Mpc general agreement is found between the slope of the REFLEX P(k) 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.
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