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

Abstract

We introduce the Southern Stellar Stream Spectroscopy Survey (S 5 ), an on-going program to map the kinematics and chemistry of stellar streams in the Southern Hemisphere. The initial focus of S 5 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 S 5 has mapped 9 DES streams and 3 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 S 5 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 S 5 , including future public data release, can be found at http://s5collab.github.io.

Galactic potential constraints from clustering in action space of combined stellar stream data

“…This phenomenal wealth of data has already facilitated the discovery of many new streams (Malhan et al 2018;Ibata et al 2019;Meingast et al 2019) and prompted further investigations of the previously known ones (Price-Whelan & Bonaca 2018; Price-Whelan et al 2019;Koposov et al 2019;Koppelman et al 2019). To gain a full 6D view of more distant streams, Gaia data must be combined with radial-velocity measurements for faint stars from current or future wide-field spectroscopic surveys such as RAVE (Kunder et al 2017), 5 (Li et al 2019), WEAVE (Dalton et al 2012), 4MOST (de Jong et al 2019), SDSS-V (Kollmeier et al 2017) etc.…”

The Milky Way’s stellar streams and globular clusters do not align in a Vast Polar Structure

“…Depending on the size of the offset (which has been observed to vary based on sky position, distance from the LMC, and stream width), this effect can make the stream normal computed using the twoanchor-point method a less reliable indicator of the orbital plane. Detailed modeling of this effect in the context of the VPOS will require radial velocities for member stars of the affected streams, something that may be possible with upcoming data releases from the S 5 survey (Li et al 2019).…”

Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-faint Satellites Grus II, Tucana IV, and Tucana V*

“…Both stars have colors and magnitudes consistent with being RGB stars at a distance modulus ∼0.4mag smaller than that of GruII and CaT metallicities of » -Fe H 2 [ ] assuming that distance. These stars can be added to the sample of spectroscopic members of the Orphan Stream being assembled by the S 5 collaboration (Li et al 2019).…”