Spectroscopic Confirmation of Five Galaxy Clusters at z > 1.25 in the 2500 sq. deg. SPT-SZ Survey

• Main Authors: Khullar, G., Bleem, L. E., Bayliss, M. B., Gladders, M. D., Benson, B. A., McDonald, M., Allen, S. W., Applegate, D. E., Ashby, M. L. N., Bocquet, S., Brodwin, M., Bulbul, E., Canning, R. E. A., Capasso, R., Chiu, I., Crawford, T. M., de Haan, T., Dietrich, J. P., Gonzalez, A. H., Hlavacek-Larrondo, J., Hoekstra, H., Holzapfel, W. L., von der Linden, A., Mantz, A. B., Patil, S., Reichardt, C. L., Saro, A., Sharon, K., Stalder, B., Stanford, S. A., Stark, A. A., Strazzullo, V.
• Format: Text
• Language: unknown
• Published: arXiv 2018
• Subjects: Astrophysics of Galaxies astro-ph.GA; FOS Physical sciences; South Pole; South pole
• Online Access: https://dx.doi.org/10.48550/arxiv.1806.01962; https://arxiv.org/abs/1806.01962

We present spectroscopic confirmation of five galaxy clusters at $1.25 < \textit{z} < 1.5$, discovered in the $2500$ deg$^{2}$ South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. These clusters, taken from a mass-limited sample with a nearly redshift independent selection function, have multi-wavelength follow-up imaging data from the X-ray to near-infrared, and currently form the most homogeneous massive high-redshift cluster sample known. We identify $44$ member galaxies, along with $25$ field galaxies, among the five clusters, and describe the full set of observations and data products from Magellan/LDSS3 multi-object spectroscopy of these cluster fields. We briefly describe the analysis pipeline, and present ensemble analyses of cluster member galaxies that demonstrate the reliability of the measured redshifts. We report $\textit{z} = 1.259, 1.288, 1.316, 1.401$ and $1.474$ for the five clusters from a combination of absorption-line (Ca II H$\&$K doublet - $3968,3934$ Å) and emission-line ([OII] $3727,3729$ Å) spectral features. Moreover, the calculated velocity dispersions yield dynamical cluster masses in good agreement with SZ masses for these clusters. We discuss the velocity and spatial distributions of passive and [OII]-emitting galaxies in these clusters, showing that they are consistent with velocity segregation and biases observed in lower redshift SPT clusters. We identify modest [OII] emission and pronounced CN and H$δ$ absorption in a stacked spectrum of $28$ passive galaxies with Ca II H$\&$K-derived redshifts. This work increases the number of spectroscopically-confirmed SZ-selected galaxy clusters at $\textit{z} > 1.25$ from three to eight, further demonstrating the efficacy of SZ selection for the highest redshift massive clusters, and enabling detailed study of these systems. : 21 pages, 10 figures, 5 tables, submitted to ApJ