Exploring the Perturbed Milky Way Disk and the Substructures of the Outer Disk

Abstract

The recent discovery of a spiral feature in the Z − V Z phase plane in the solar neighborhood implies that the galactic disk has been remarkably affected by a dwarf galaxy passing through it some hundreds of millions of years ago. Using 429,500 Large Sky Area Multi-Object Fibre Spectroscopic Telescope K giants stars, we show that the spiral feature exists not only in the solar vicinity but it also extends to about 15 kpc from the Galactic center and then disappears beyond this radius. Moreover, we find that when the spiral features in a plot of V ϕ as a function of position in the Z − V Z plane at various galactocentric radii are remapped to the R − Z plane, the spiral can explain well the observed asymmetric velocity substructures. This is evidence that the phase spiral features are the same as the bulk motions found in previous work as well as this work. Test particle simulations and N-body simulations show that an encounter with a dwarf galaxy a few hundred million years ago will induce a perturbation in the galactic disk. In addition, we find that the last impact of Sgr dSph can also contribute to the flare. As a consequence of the encounter, the distribution function of disk stars at a large range of radii is imprinted by the gravitational perturbation.

The Flare and Warp of the Young Stellar Disk traced with LAMOST DR5 OB-type stars

“…With the help LAMOST K giant stars and two types of simulations, Xu et al (2020) pointed out the external perturbations might influence the outer disk beyond solar neighborhood and revealed that the flaring could be explained by perturbations qualitatively, which supports our viewpoints here about the flaring. Combining young OB type Stars and old K giant stars we could infer that the sensitive time of the flaring features to the possible perturbations might from very early time in OB population to the relatively late time in K giant population.…”

“…In addition to the aforementioned disturbances, Cheng et al (2019) proposed another case, that is saying, a few decades ago, the dark matter sub-halo perturbed the disk and left marks on these young stars. Similar perturbation scenarios such as warp, stream, satellites, dwarf galaxies, dark matter sub-halos are also mentioned in Wang et al (2018aWang et al ( , 2020a; Khanna et al (2019);Bland-Hawthorn et al (2019); Xu et al (2020) and reference therein.…”

Overview of the LAMOST survey in the first decade

“…In particular, the stellar-mass density at a radius of $8 kpc is significantly higher than previous estimates 135 by approximately 0.016 M 1 /pc 3 . 47 The disk flaring phenomenon was clearly revealed by LAMOST 47,136,137 (Figure 7), which was found to be a ubiquitous phenomenon for all monoage populations. Complex features in the stellar distribution throughout the outer disk revealed by LAMOST 47,138 reflect a significantly perturbated disk (Figure 7) evolution history.…”

Snails Across Scales: Local and Global Phase-Mixing Structures as Probes of the Past and Future Milky Way

“…In particular, simulations of a Sgr-like satellite impacting a MW-like disk that were developed to fit the pre-Gaia data were shown to contain analogous manifestation of both the local and global signatures of vertical disequilibrium with similar spatial and velocity scales (Laporte et al 2019). Other works have reinforced these local-global connections with further views of the data, tailored simulations and analytic models (Xu et al 2020;Bland-Hawthorn & Tepper-Garcia 2020;Widrow et al 2020;Bennett & Bovy 2021).…”