XMMU J100750.5+125818: A strong lensing cluster at z=1.082

Abstract: We report on the discovery of the X-ray luminous cluster XMMU J100750.5+125818 at redshift 1.082 based on 19 spectroscopic members, which displays several strong lensing features. SED modeling of the lensed arc features from multicolor imaging with the VLT and the LBT reveals likely redshifts ~2.7 for the most prominent of the lensed background galaxies. Mass estimates are derived for different radii from the velocity dispersion of the cluster members, M_200 ~ 1.8 10^{14} Msun, from the X-ray spectral parameters, M_500 ~ 1.0 10^{14} Msun, and the largest lensing arc, M_SL ~ 2.3 10^{13} Msun. The projected spatial distribution of cluster galaxies appears to be elongated, and the brightest galaxy lies off center with respect to the X-ray emission indicating a not yet relaxed structure. XMMU J100750.5+125818 offers excellent diagnostics of the inner mass distribution of a distant cluster with a combination of strong and weak lensing, optical and X-ray spectroscopy.