The Milky Way's halo in 6D: Gaia's Radial Velocity Spectrometer performance

TL;DR

This paper evaluates Gaia's Radial Velocity Spectrometer performance, highlighting the impact of straylight on limiting magnitude, software upgrades to improve performance, and implications for mapping the Milky Way's halo in 6D.

Contribution

It provides an assessment of RVS performance post-commissioning, including software improvements and their effects on Gaia's ability to study the Milky Way's halo in six dimensions.

Findings

Straylight reduces the limiting magnitude of RVS.

Software upgrades can recover approximately 0.14 mag of performance.

Gaia's RVS achieves 15 km/s precision for V between 15 and 16 mag.

Abstract

Gaia's Radial Velocity Spectrometer (RVS) has been operating in routine phase for over one year since initial commissioning. RVS continues to work well but the higher than expected levels of straylight reduce the limiting magnitude. The end-of-mission radial-velocity (RV) performance requirement for G2V stars was 15 km/s at V = 16.5 mag. Instead, 15 km/s precision is achieved at 15 < V < 16 mag, consistent with simulations that predict a loss of 1.4 mag. Simulations also suggest that changes to Gaia's onboard software could recover ~0.14 mag of this loss. Consequently Gaia's onboard software was upgraded in April 2015. The status of this new commissioning period is presented, as well as the latest scientific performance of the on-ground processing of RVS spectra. We illustrate the implications of the RVS limiting magnitude on Gaia's view of the Milky Way's halo in 6D using the Gaia Universe Model Snapshot (GUMS).