Observations of Massive Galaxy Clusters from the All-Sky Survey with the eROSITA Telescope Onboard the SRG Space Observatory

We present the results of our search for massive galaxy clusters among extended X-ray sources from the SRG/eROSITA survey using data from the Planck survey and data from optical and infrared sky surveys. Optical observations of these clusters are carried out with the 6-m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences (BTA), the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University (AZT-33IK), and the 1.5-m Russian-Turkish telescope (RTT-150). We provide data on the optical identifications and spectroscopic redshift measurements for 11 massive galaxy clusters with masses higher than $M_{500}≈ 6× 10^{14}M_{\odot}$ located at redshifts $z≈ 0.3$-$1$. Such clusters are very rare objects; most of the clusters with such a high mass in the observable Universe have already been detected previously by the Sunyaev-Zeldovich effect in the Planck all-sky survey. Being anomalous, they can be sensitive indicators of possible deviations of the cosmology from the standard $Λ CDM$ model with a quasi-flat spectrum of initial Gaussian perturbations.