Optical identifications of high-redshift galaxy clusters from Planck
  Sunyaev-Zeldovich survey
  We present the results of optical identifications and spectroscopic redshifts
measurements for galaxy clusters from 2-nd Planck catalogue of
Sunyaev-Zeldovich sources (PSZ2), located at high redshifts, $z\approx0.7-0.9$.
We used the data of optical observations obtained with Russian-Turkish 1.5-m
telescope (RTT150), Sayan observatory 1.6-m telescope, Calar Alto 3.5-m
telescope and 6-m SAO RAS telescope (Bolshoi Teleskop Alt-azimutalnyi, BTA).
Spectroscopic redshift measurements were obtained for seven galaxy clusters,
including one cluster, PSZ2 G126.57+51.61, from the cosmological sample of PSZ2
catalogue. In central regions of two clusters, PSZ2 G069.39+68.05 and PSZ2
G087.39-34.58, the strong gravitationally lensed background galaxies are found,
one of them 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, $z\approx0.8$.
