The XMM-LSS survey

We present five newly found galaxy clusters at $z>0.6$ from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have sufficient spectroscopically confirmed member galaxies that an estimate of the velocity dispersion is possible: XLSSC 001 at $z=0.613$ and $\sigma_V=867^{+80}_{-60}$ km s-1, XLSSC 002 at $z=0.772$ and $\sigma_V=524^{+267}_{-116}$ km s-1 and XLSSC 003 at $z=0.839$ and $\sigma_V=780^{+137}_{-75}$ km s-1. These three clusters have X-ray bolometric luminosities $L_{\rm X} \sim 1{-}3 \times 10^{44}$ erg s-1 and temperatures $2{-}4$ keV, and consequently are less massive than previously known clusters at similar redshifts, but nevertheless they follow the low redshift scaling relations between $L_{\rm X}, T$ and $\sigma_v$, within the limits of the measurement errors. One of the clusters, XLSSC 004, is detected independently as an overdensity of galaxies of a colour $R-z'=1.4$ that matches the redshift of the central galaxy $z=0.87$, although it cannot unambiguously be confirmed by the spectroscopic observations alone. The highest redshift candidate cluster pertaining to this paper, XLSSC 005, is most likely a double cluster complex at a redshift around unity, associated with an extended X-ray source with probable substructure.