Abstract
We present XMM-Newton observations of three optically selected z > 0.6 clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and - unlike other high-redshift, optically selected clusters - are consistent with the T$-\sigma$ and L$_{X-\sigma}$ relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by z ~ 0.8.
Highlights
D searches for galaxy overdensities or through X-ray detection of the intracluster gas
If the optically selected sources are representative of the high-redshift cluster population in general, their deviation from the X-ray–optical scaling relations would indicate significant evolution of the intracluster medium (ICM) since z ∼
We identified optical counterparts to the X-ray point sources on astrometrically corrected 60-min exposures obtained with the WideField Imager (WFI) at the European Southern Observatory (ESO)/MPG 2.2-m telescope which cover the full XMM–Newton FOV (Clowe et al, in preparation)
Summary
Several authors have recently addressed the question of whether X-ray and optical detection techniques are equal probes of the cluster population (e.g. Donahue et al 2001, 2002), generally concluding that they are not At lower redshift, it appears that optical surveys may be able to detect less-massive and/or lessevolved systems. If the optically selected cluster surveys at high redshift have preferentially selected these forming systems, their deviation from the LX –σ and T–σ relations would not necessarily imply the evolution in the ICM properties of the general cluster population or indicate a strong bias in X-ray-selected samples of virialized clusters. X-ray and optically selected high-redshift cluster samples is clearly vital to know how well these survey techniques reflect the underlying mass distribution, and may provide valuable information about the mechanisms and time-scales of mass congregation and ICM heating in forming structures. Errors throughout are quoted at the 90 per cent confidence level
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