Spectroscopic Confirmation and Velocity Dispersions for 20 Planck Galaxy Clusters at 0.16 < z < 0.78

We present Gemini and Keck spectroscopic redshifts and velocity dispersions for 20 clusters detected via the Sunyaev–Zel'dovich (SZ) effect by the Planck space mission, with estimated masses in the range 2.3 x 10^(14) M⊙ < M^(Pl)_(500) < 9.4 x 10^(14) M⊙.. Cluster members were selected for spectroscopic follow-up with Palomar, Gemini, and Keck optical and (in some cases) infrared imaging. Seven cluster redshifts were measured for the first time with this observing campaign, including one of the most distant Planck clusters confirmed to date, at z = 0.782 ± 0.010, PSZ2 G085.95+25.23. The spectroscopic redshift catalogs of members of each confirmed cluster are included as online tables. We show the galaxy redshift distributions and measure the cluster velocity dispersions. The cluster velocity dispersions obtained in this paper were used in a companion paper to measure the Planck mass bias and to constrain the cluster velocity bias.