We present a kinematic analysis of a sample of 23,908 G- and K-type dwarfs in the Galactic disk. Based on the $α$-abundance ratio, [$α$/Fe], we separated our sample into low-$α$ thin-disk and high-$α$ thick-disk stars. We find a $V_{\rm ϕ}$ gradient of $-$28.2 km s$^{-1}$ dex$^{-1}$ over [Fe/H] for the thin disk, and an almost flat trend of the velocity dispersions of $V_{\rm R}$, $V_{\rm ϕ}$, and $V_{\rm Z}$ components with [Fe/H]. The metal-poor (MP; [Fe/H] $<$ $-$0.3) thin-disk stars with low-$V_{\rm ϕ}$ velocities have high eccentricities ($e$) and small perigalacticon distances ($r_{\rm p}$), while the high-$V_{\rm ϕ}$ MP thin-disk stars possess low $e$ and large $r_{\rm p}$. Interestingly, half of the super metal-rich ([Fe/H] $>$ $+$0.1) stars in the thin disk exhibit low-$e$, solar-like orbits. Accounting for the inhomogeneous metallicity distribution of the thin-disk stars with various kinematics requires radial migration by churning $-$ it apparently strongly influences the current structure of the thin disk; we cannot rule out the importance of blurring for the high-$e$ stars. We derive a rotation velocity gradient of $+$36.9 km s$^{-1}$ dex$^{-1}$ for the thick disk, and decreasing trends of velocity dispersions with increasing [Fe/H]. The thick-disk population also has a broad distribution of eccentricity, and the number of high-$e$ stars increases with decreasing [Fe/H]. These kinematic behaviors could be the result of a violent mechanism, such as a gas-rich merger or the presence of giant turbulent clumps, early in the history of its formation. Dynamical heating by minor mergers and radial migration may also play roles in forming the current thick-disk structure.
The nucleus of our nearest, large galactic neighbor, M31, contains an eccentric nuclear disk--a disk of stars on eccentric, apsidally-aligned orbits around a supermassive black hole (SMBH). Previous studies of eccentric nuclear disks considered only an isolated disk, and did not study their dynamics under galaxy mergers (particularly a perturbing SMBH). Here, we present the first study of how eccentric disks are affected by a galactic merger. We perform N-body simulations to study the disk under a range of different possible SMBH initial conditions. A second SMBH in the disk always disrupts it…
The stellar mass, size and rotational velocity of galactic disks all grow from redshift ~2 to the present by amounts that are estimated from observationally derived scaling relations. The product of these three quantities, the angular momentum of stellar disks, is then estimated to grow by a remarkably large factor, between ~20 and ~50, whereas other evidences suggest a more moderate increase. This requires that the specific angular momentum of the accreted gas should systematically increase with time while remaining co-rotational with the disk over most of the last ~10 Gyr. Thus, the baryonic…
Using a sample of nearly 140,000 red clump stars selected from the LAMOST and Gaia Galactic surveys, we have mapped mean vertical velocity $\overline{V_{z}}$ in the $X$-$Y$ plane for a large volume of the Galactic disk (6 $< R < 16$ kpc; $-20 <ϕ< 50^{\circ}$; $|Z| < 1$ kpc). A clear signature where $\overline{V_{z}}$ increases with $R$ is detected for the chemically thin disk. The signature for the thick disk is however not significant, in line with the hot nature of this disk component. For the thin disk, the warp signature shows significant variations in both radial and azimuthal directions,…
We investigate the three-dimensional asymmetrical kinematics and present time stamps of the Milky Way disk between Galactocentric distances of $R=12$ and 15 \,kpc, using red clump stars selected from the LAMOST Galactic survey, also with proper motion measurements provided by the Gaia DR2. We discover velocity substructure above the Galactic plane corresponding to a density dip found recently ("south-middle opposite" density structure[R $\sim$ 12-15 \,kpc, Z $\sim$ 1.5 \,kpc] discovered in \citet{Wang2018b, Wang2018c}) in the radial and azimuthal velocity. For the vertical velocity, we detect …
We present a novel method for determining the total matter surface density of the Galactic disk by analysing the kinematics of a dynamically cold stellar stream that passes through or close to the Galactic plane. The method relies on the fact that the vertical component of energy for such stream stars is approximately constant, such that their vertical positions and vertical velocities are interrelated via the matter density of the Galactic disk. By testing our method on mock data stellar streams, with realistic phase-space dispersions and Gaia uncertainties, we demonstrate that it is applicab…
Galacto-forensic of LMC's orbital history as a probe for the dark matter potential in the outskirt of the Galaxy
观测到的大麦哲伦云和小麦哲伦云的三维速度为探测星系晕外围的星系势提供了机会。Besla et al.基于银河系势的正则NFW模型，（2007）重建了LMC和SMC的轨道，并认为它们目前正在第一次围绕银河系的近银河系轨道上。出于最近几次修订的太阳的运动围绕银河系中心，我们重新检查LMC的轨道历史，并表明它敏感地依赖于暗物质的质量分布超出其目前的银河系距离。我们利用数值模拟的结果，考虑一系列可能的结构和演化模型的银河系的潜力。我们发现，在理论和观测的不确定性，它是可能的大麦哲伦星云有多个近银河系通道的哈勃时间尺度上，特别是如果银河系的圆速度在太阳的位置大于$\sim 228$公里秒$^{-1}$。基于这些模型，更准确地确定大麦哲伦星系的运动可以用来确定星系晕外围的暗物质分布。
We have applied our method for weighing the Galactic disk using phase-space spirals to the Gaia EDR3 proper motion sample. For stars in distant regions of the Galactic disk, the latitudinal proper motion has a close projection with vertical velocity, such that the phase-space spiral in the plane of vertical position and vertical velocity can be observed without requiring that all stars have available radial velocity information. We divided the Galactic plane into 360 separate data samples, each corresponding to an area cell in the Galactic plane in the distance range of 1.4-3.4 kpc, with an ap…
Excitation of coupled stellar motions in the Galactic Disk by orbiting satellites
我们使用一组高分辨率的N体模拟银河系盘研究其相互作用的人口的卫星宇宙学预测。一个模拟表明，具有不同速度的大质量卫星多次通过磁盘产生摆动，在恒星磁盘的正面投影中出现环。它们还在盘的外部产生耀斑，并通过弯曲波逐渐加热盘。一个不同的数值实验表明，一个像人马座矮星系一样大的卫星穿过盘将驱动低密度区域恒星的水平和垂直耦合振荡，伴随着小的显著的相关加热。这个实验表明，在这些低密度区域的恒星的垂直偏移可以超过1千秒差距的太阳附近，类似于最近在当地检测到的相干垂直振荡。它们也可以引起非零的垂直流运动，大到10-20 km s $^{-1}$，与最近在银河系盘中的观测结果一致。这种现象表现为局部环，并伴有适度的盘加热。
Collisions between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud
银河系的高速云（HVC）可能包括一个被暗物质迷你晕限制并向银河系盘下落的子群。本文首次对以暗物质为主的HVC与弱磁化星系盘碰撞进行了磁流体动力学模拟研究。我们的HVC的重子质量为$5 \times 10^6\,$ M $_{\odot}$，暗物质微晕质量为0、$3 \times 10^8$或$1 \times 10^9\,$ M $_{\odot}$。它们是以史密斯云为模型的，据说史密斯云在7000万年前与圆盘相撞。我们发现，在所有情况下，云与星系盘的碰撞都会在星系盘上产生一个洞，完全分散云，并在星系盘的远端形成一个气泡状结构。相反，当存在时，暗物质微晕继续沿着其轨迹畅通无阻。之后，随着微晕穿过气泡结构和星系晕，它在重子物质中吸积到$6.0 \times 10^5\,$ M $_{\odot}$，这取决于磁场和微晕引力的强度。这些模拟表明，如果史密斯云与一个暗物质微晕有关，并与银河系盘碰撞，那么微晕已经吸积了观测到的气体。然而，如果史密斯云是暗物质自由的，它是第一次接近磁盘。这些模拟还表明，根据磁场的强度，暗物质要么集中在云的头部，要么集中在云的附近，这一点可以为间接的暗物质搜索提供信息。
We report measurements of parallax and proper motion for four 22 GHz water maser sources as part of VERA Outer Rotation Curve project. All sources show Galactic latitudes of $>$ 2$^{\circ}$ and Galactocentric distances of $>$ 11 kpc at the Galactic longitude range of 95$^{\circ}$ $< l <$ 126$^{\circ}$. The sources trace the Galactic warp reaching to 200$\sim$400 pc, and indicate the signature of the warp to 600 pc toward the north Galactic pole. The new results along with previous results in the literature show the maximum height of the Galactic warp is increased with Galactocentric distance. …
Mapping the Galactic disk with the LAMOST and Gaia Red clump sample: VIII: Mapping the kinematics of the Galactic disk using mono-age and mono-abundance stellar populations
