X-ray luminous radio-quiet high redshift QSOs in the ROSAT All-Sky Survey

X-ray luminous radio-quiet high redshift QSOs are rare and can be used for the investigation of several important astronomical questions. We have cond ucted a large area survey for radio-quiet high redshift QSOs in the ROSAT A ll-Sky Survey, from which QSO candidates are selected using the digitized o bjective prism spectra from the Hamburg Quasar Survey. The 22 candidates wi th Galactic latitudes larger than 35 degrees were observed with the 2.16m t elescope at Xinglong station of Beijing Astronomical Observatory. Among the 19 new QSQs in our sample, six are radio-quiet QSOs with redshifts larger than 1.3 and three of them have redshifts larger than 2. Thus we have doubl ed the number of known X-ray luminous, radio-quiet high redshift QSOs in th e surveyed sky area. The distribution of f(1.4) (GHz)/f(1keV) Of radio-loud and radio-quiet QSOs in this area shows two well separated peaks. This can be taken as an evidence for different emission mechanisms of the observed X-rays in the two subgroups.