The southern stellar stream spectroscopic survey (S5): Overview, target selection, data reduction, validation, and early science

T. S. Li, S. E. Koposov, D. B. Zucker, G. F. Lewis, K. Kuehn, J. D. Simpson, A. P. Ji, N. Shipp, Y. Y. Mao, M. Geha, A. B. Pace, A. D. Mackey, S. Allam, D. L. Tucker, G. S. Da Costa, D. Erkal, J. D. Simon, J. R. Mould, S. L. Martell, Z. WanG. M. De Silva, K. Bechtol, E. Balbinot, V. Belokurov, J. Bland-Hawthorn, A. R. Casey, L. Cullinane, A. Drlica-Wagner, S. Sharma, A. K. Vivas, R. H. Wechsler, B. Yanny

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We introduce the southern stellar stream spectroscopy survey (S5), an on-going program to map the kinematics and chemistry of stellar streams in the southern hemisphere. The initial focus of S5 has been spectroscopic observations of recently identified streams within the footprint of the dark energy survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9 m Anglo-Australian Telescope's 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from Gaia DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far S5 has mapped nine DES streams and three streams outside of DES; the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake a Milky Way halo survey and a low-redshift galaxy survey. This paper presents an overview of the S5 program, describing the scientific motivation for the survey, target selection, observation strategy, data reduction, and survey validation. Finally, we describe early science results on stellar streams and Milky Way halo stars drawn from the survey. Updates on S5, including future public data releases, can be found at

Original languageEnglish
Pages (from-to)3508-3531
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 1 Dec 2019

Bibliographical note

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 490, Issue 3, December 2019, Pages 3508–3531, Copyright 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


  • Galaxies: dwarf
  • Galaxy: halo
  • Galaxy: kinematics and dynamics
  • Globular clusters: general


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