An extension of the SHARC survey

Aims. We report on our search for distant clusters of galaxies based on optical and X-ray follow up observations of X-ray candidates from the SHARC survey, and based on the assumption that the absence of bright optical or radio counterparts to possibly extended X-ray sources could mean that they are distant clusters. Methods. We have obtained deep optical images and redshifts for several of these objects and analyzed archive XMM-Newton or Chandra data where applicable. Results. In our list of candidate clusters, two are probably galaxy structures at redshifts of z ∼ 0.51 and 0.28. Seven other structures are possibly galaxy clusters between z ~ 0.3 and 1. Three sources are identified with QSOs and are thus likely to be X-ray point sources, and six more also probably fall in this category. One X-ray source is spurious or variable. For 17 other sources, the data are too sparse at this time to put forward any hypothesis on their nature. We also serendipitously detected a cluster at z = 0.53 and another galaxy concentration which is probably a structure with a redshift in the [0.15-0.6] range. Conclusions. We discuss these results within the context of future space missions to demonstrate the necessity of a wide field of view telescope optimized for the 0.5-2 keV range.