A Panoramic Landscape of the Sagittarius Stream in Gaia DR2 Revealed with the STREAMFINDER Spyglass

Abstract

We present the first full six-dimensional panoramic portrait of the Sagittarius stream, obtained by searching for wide stellar streams in the Gaia DR2 data set with the STREAMFINDER algorithm. We use the kinematic behavior of the sample to devise a selection of Gaia RR Lyrae, providing excellent distance measurements along the stream. The proper motion data are complemented with radial velocities from public surveys. We find that the global morphological and kinematic properties of the Sagittarius stream are still reasonably well reproduced by the simple Law & Majewski model (LM10), although the model overestimates the leading arm and trailing arm distances by up to ∼15%. The sample newly reveals the leading arm of the Sagittarius stream as it passes into very crowded regions of the Galactic disk toward the Galactic anticenter direction. Fortuitously, this part of the stream is almost exactly at the diametrically opposite location from the Galactic center to the progenitor, which should allow an assessment of the influence of dynamical friction and self-gravity in a way that is nearly independent of the underlying Galactic potential model.