Tracing the hidden AGN activity in the EROs population

We propose to perform with XMMNewton a hard Xray followup of the largestsample of optically selected Extremely Red Objects (EROs, RK > 5) availableto date. This study is aimed at understanding the nature of the EROS populationand to better assess the relative fraction of heavily obscured AGN, dustystarforming galaxies and old passively evolving ellipticals at high redshift.This is possible only with XMM since it couples good angular resolutionand excellent sensitivity at high energies thus allowing for accurate spectralanalysis. The proposed observations will allow us to push to fainter Xrayfluxes the detection of EROs and to constrain their spectral properties thus providing a unique tool to understand their nature. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]