Optical identifications of high-redshift galaxy clusters from the Planck Sunyaev–Zeldovich Survey

We present the results of optical identifications and spectroscopic redshift measurements for galaxy clusters from the second Planck catalogue of Sunyaev–Zeldovich sources (PSZ2) located at high redshifts, z ≈ 0.7−0.9. We used the data of optical observations with the Russian–Turkish 1.5-mtelescope (RTT-150), the Sayan Observatory 1.6-m telescope, the Calar Alto 3.5-m telescope, and the 6-m SAO RAS telescope (BTA). The spectroscopic redshift measurements were obtained for seven galaxy clusters, including one cluster, PSZ2 G126.57+51.61, from the cosmological sample of the PSZ2 catalogue. In the central regions of two clusters, PSZ2 G069.39+68.05 and PSZ2 G087.39−34.58, we detected arcs of strong gravitational lensing of background galaxies, one of which is at redshift z = 4.262. The data presented below roughly double the number of known galaxy clusters in the second Planck catalogue of Sunyaev–Zeldovich sources at high redshifts, z ≈ 0.8.