The low number of confirmed and well studied FGs has hampered so far the attempts to constrain the abundance and properties of these systems. The number of well studied FG is about 10, with only 7 temperature estimates; moreover they are spread over a large redshift range. Using SDSS and RASS data, we assembled one of the largest comprehensive and objective samples of FG candidates available in the literature. We propose to use XMM to confirm the nature of 12 optimally selected candidates, more than doubling the number of known FGs. Their X-ray properties will be compared to a sample of field ellipticals and to cosmological simulations, in order to understand if FGs represent the final evolutionary stage of galaxy groups or just the tip of the galaxy group distribution with peculiar LF.
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