Selected Active Galactic Nuclei from SRG/eROSITA Survey: Optical and IR Observations in 2021 and 2022 with the 2.5-m Telescope at the Caucasian Mountain Observatory of SAI MSU

We report the results of optical spectroscopy of eight highly variable X-ray sources—AGN candidates from all-sky survey of the eROSITA telescope of the Spectrum-Roentgen-Gamma Space Observatory—performed with the TDS spectrograph (3600–7500 Å, \(R\approx 2000\)) attached to the 2.5-m telescope of the Caucasian Mountain Observatory of Sternberg Astronomical Institute of M.V. Lomonosov Moscow State University. We determined the redshifts of the sources from the emission and absorption lines in their spectra. At least five objects can be classified as Seyfert galaxies. We performed pilot infrared photometry of three distant quasars with \(z>5\) using the ASTRONIRCAM camera and show that on the ‘‘\((z-J){-}(J-W1)\)’’ diagram the distant quasars studied can be confidently distinguished from Galactic red and brown dwarfs. This result proves the possibility of preliminary classification of distant X-ray quasar candidates by their IR colors for further detailed spectroscopic study on large telescopes.