The HELLAS2XMM survey

We present VLT near-IR spectroscopic observations of three X-ray sources characterized by extremely high X-ray–to–optical ratios ($\rm X/O>40$), extremely red colors ($6.3<R-K<7.4$, i.e. EROs) and bright infrared magnitudes ($17.6<K<18.3$). These objects are very faint in the optical, making their spectroscopic identification extremely challenging. Instead, our near-IR spectroscopic observations have been successful in identifying the redshift of two of them ($z=2.08$ and $z=1.35$), and tentatively even of the third one ($z=2.13$). When combined with the X-ray properties, our results clearly indicate that all these objects host obscured QSOs ($4\times10^{44}<L_{2{-}10~\rm keV}<1.5\times 10^{45}~\rm erg~s^{-1}$, $2\times10^{22}<N_{\rm H}