doi.eso.org

• Ibata, Rodrigo [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]
• Battaglia, Giuseppina [Canary Islands Institute of Astrophysics, Tenerife, Spain]
• Bellazzini, Michele [INAF–Bologna Astrophysics and Space Science Observatory, Italy]
• Clementini, Gisella [INAF–Bologna Astrophysics and Space Science Observatory, Italy]
• Errani, Raphael [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]
• Famaey, Benoit [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]
• Garofalo, Alessia [INAF–Bologna Astrophysics and Space Science Observatory, Italy]
• Hill, Vanessa [Lagrange Laboratory, Côte d’Azur Observatory, Côte d’Azur University, Nice, France]
• Martin, Nicolas [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]
• Mucciarelli, Alessio [INAF–Bologna Astrophysics and Space Science Observatory, Italy]
• Monari, Giacomo [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]
• Posti, Lorenzo [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]
• Skúladóttir, Ása [Department of Physics and Astronomy, University of Florence, Italy]
• Sollima, Antonio [INAF–Bologna Astrophysics and Space Science Observatory, Italy]
• Siebert, Arnaud [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]
• Thomas, Guillaume [Canary Islands Institute of Astrophysics, Tenerife, Spain]
• Malhan, Khyati [Max Planck Institute for Astronomy, Heidelberg, Germany]
• Freundlich, Jonathan [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]
• Arentsen, Anke [Institute of Astronomy, University of Cambridge, UK]
• Yuan, Zhen [Strasbourg Astronomical Observatory, CNRS, University of Strasbourg, France]

The 4GRoundS survey will measure the radial velocities and metallicities of southern RR Lyrae stars in Gaia Data Release 3. These stars have excellent photometric distances, allowing the exquisite Gaia proper motions to be converted into physically useful transverse velocities. Armed with the missing radial velocity, 4GRoundS will provide the community with a dataset that will enable studies of the orbital structure of the halo and outer disc, and allow realistic modelling of these components. It will also enable the identification of coherent dynamically cold streams. Together these analyses will map the mass of the Milky Way out to 100 kpc and test models of the dark sector.