This table contains a catalog of 128 X-ray galaxy groups, covering a redshift (z) range 0.04 < z <1.23, selected in the ~ 3 deg² part of the CFHTLS W1 field overlapping XMM-Newton observations performed under the XMM-LSS project. The authors carry out a statistical study of the redshift evolution out to redshift 1 of the magnitude gap between the first and the second brightest cluster galaxies of a well defined mass-selected group sample. They find that the slope of the relation between the fraction of groups and the magnitude gap steepens with redshift, indicating a larger fraction of fossil groups at lower redshifts. They also find that 22.2% +/- 6% of their groups at z <= 0.6 are fossil groups. The authors compare their results with the predictions of three semi-analytic models based on the Millennium simulation. The intercept of the relation between the magnitude of the brightest galaxy and the value of magnitude gap becomes brighter with increasing redshift. This trend is steeper than the model predictions which the authors attribute to the younger stellar age of the observed brightest cluster galaxies. This trend argues in favor of stronger evolution of the feedback from active galactic nuclei at z < 1 compared to the models. The slope of the relation between the magnitude of the brightest cluster galaxy and the value of the gap does not evolve with redshift and is well reproduced by the models, indicating that the tidal galaxy stripping, put forward as an explanation of the occurrence of the magnitude gap, is both a dominant mechanism and sufficiently well modeled. In this study, the authors analyzed the XMM-Newton observations of the CFHTLS wide (W1) field as a part of the XMM-LSS survey (Pierre et al., 2007, MNRAS, 382, 279). The details of the observations and the data reduction are presented in Bielby et al. (2010, A&A, 523, A66). The authors concentrate on the low-z counterparts of the X-ray sources and use all XMM-Newton observations performed until 2009, covering an area of 2.276 x 2.276 square degrees. The CFHTLS wide observations were carried out in the period between 2003 and 2008, covering an effective survey area of ~ 154 square degrees. The optical images and data of the CFHTLS were obtained with the MegaPrime instrument mounted on the CFHT in the five filters u*, g', r', i' and z'. This table was created by the HEASARC in December 2014 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/566/A140">CDS catalog J/A+A/566/A140</a> file table1.dat. This is a service provided by NASA HEASARC .