1.Space Research Institute,Russian Academy of Sciences,Moscow,Russia;2.Institute of Solar–Terrestrial Physics,Russian Academy of Sciences, Siberian Branch,Irkutsk,Russia
Abstract:
We present the results of optical spectroscopy for 19 quasar candidates at photometric redshifts zphot ? 3, 18 of which enter into the Khorunzhev et al. (2016) catalog (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the 3XMM-DR4 catalog of the XMM-Newton serendipitous survey. We have performed spectroscopy for a quasi-random sample of new candidates at the 1.6-m AZT-33IK telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory. The spectra at AZT-33IK were taken with the new low- and medium-resolution ADAM spectrograph that was produced and installed on the telescope in 2015. Fourteen of the 18 candidates actually have turned out to be quasars; 10 of them are at spectroscopic redshifts zspec > 3. The high purity of the sample of new candidates suggests that the purity of the entire K16 catalog of quasars is probably 70–80%. One of the most distant (zspec = 5.08) optically bright (i′ ? 21) quasars ever detected in X-ray surveys has been discovered.