The bar of the Galaxy is believed to slow down. We use an axisymmetric background potential plus a central bar model to perform the test particle simulations in order to investigate the possible origin of the phase space spirals and the thin-disc-like low-metallicity stars (VMPs). The Gaia data reveal a two-armed phase spiral pattern in the local plane inside the solar radius. On the contrary, the phase spiral pattern becomes single armed when outside the solar radius. We use a steadily rotating central bar to perform particle test integrations, no phase spiral is perceptible in the plane under this model. We then show a decelerating bar model can produce a strong two-armed phase-spiral. For the VMPs, the bar with constant pattern speed cannot bring these stars from the bulge to solar vicinity. While for the decelerating bar, the bulge stars can be carried outwards and mainly constrained within the co-rotation trapped regions by the bar. We also find that the only 8%~12% thin disc like metal poor stars in the solar vicinity comes from the bulge. As a conclusion, the central bar of the Galaxy is indeed decreasing.and this model can be used to interpret various features in the Galaxy
BIO
Dr. Li got his Ph.D in National Astronomical Observatories, Chinese Academy of Sciences (NAOC) in 2019. Then he worked in the University of Oxford as a post-doc researcher on modelling the Galaxy via distribution function (DF) method. Currently, he works in Strasbourg Observatory as a post-doc researcher focusing on the perturbation of the Galaxy by the central bar. His interest mainly lies in the Galactic dynamics including DF based analytical modelling and simulation works. He is currently a core member of the WEAVE LRdisc project. He also participates in the consortium of the GaiaNIR project.
