Search for Distant and X-ray Luminous Quasars during the SRG/eROSITA Sky Survey (the DaLeQo Program). The First Results from Observations at the BTA Telescope

We discuss the results of our spectroscopy for 17 candidates for distant quasars selected by the SRGz classification system based on data from the first and second sky surveys with the eROSITA telescope onboard the SRG X-ray observatory. Most of the quasar candidates were selected within the DaLeQo observing program, whose goal is a search for the most X-ray luminous quasars with luminosities L_2-10 keV≳ 5× 10^45 erg s ^-1 at redshifts z≳ 3 . Our spectroscopic observations were carried out at the 6-m BTA telescope with the SCORPIO-2 spectrograph. We have managed to confirm eight new X-ray quasars at z_spec≳ 3 , including the quasar SRGe J020142.8-015347 at z_spec=5.02 . Owing to the large diameter of the BTA mirror and the high quantum efficiency of the SCORPIO-2 spectrograph in the range 6000–9000 Å, we have managed to measure the С IV (1549 Å) line parameters and to estimate the supermassive black hole masses and accretion rates for seven quasars.