Spectroscopic Confirmation of Five Galaxy Clusters at z > 1.25 in the 2500 deg 2 SPT-SZ Survey

• Published in: The Astrophysical Journal
• 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.
• Language: unknown
• Published: 2022
• Subjects: South Pole; South pole
• Online Access: http://www.osti.gov/servlets/purl/1494711; https://www.osti.gov/biblio/1494711; https://doi.org/10.3847/1538-4357/aaeed0

We present spectroscopic confirmation of five galaxy clusters at 1.25 < 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-IR, 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 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 - λλ3968,3934Å) and emission-line ([OII] λλ3727,3729Å) 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 Hδ 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 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.