Kinematic-Chemical analysis and Time tagging for the Diagonal Ridge Structure of the Galactic Outer Disk with LAMOST Red Giant Branch Stars

Abstract

We investigate the kinemato-chemical distribution of a sample of Red Giant Branch (RGB) stars from the LAMOST survey crossed matched with Gaia DR2 proper motions, and present the time tagging for the well-known ridge structures (diagonal distributions in the 𝑅, 𝑉 𝜙 plane) in the range of Galactocentric distance R = 8 to 18 kpc. We detect six long-lived ridge structures, including five ridges apparent in the radial velocity distribution and one ridge apparent in the vertical velocity. Based on an analysis of the evolution of the angular momentum distribution, we find that four ridges are relatively stationary, while another is evolving with time, which is confirmed by the difference analysis at different populations and supporting that there might be two kinds of dynamical origins with possible coupling mechanisms. Furthermore, ridge features are also vividly present in the chemical properties ([Fe/H], [𝛼/Fe]), in particular for the mass distribution (M). The comparison between the north and south hemispheres of the Galaxy does not show a clear asymmetry in the phase space location even though the amplitude (e.g., vertical velocity) is asymmetrical. Moreover, we find that diagonal ridge structures may affect the shape of the rotation curve, which is manifested as fluctuations and undulations on top of a smooth profile.

The Dark Matter Tidal Stripping History of the Sagittarius Core with N-body simulations

“…In summary, the model presented by Wang et al (2022) that reproduces the Sgr stream including its bifurcation behavior is also able to successfully reproduce most of the Sgr core properties as it is shown in this work. Without specific fine-tuning, the modeling reproduces most of the core morphology, including the bar, as well as most of its kinematics, including the tidally removed stars at its bar edges, which are forming the Sgr stream.…”

“…Here we give a concise review of our high resolution modeling for which the mass resolution for dwarf galaxy is one hundred times better than the fiducial model in Wang et al (2022), i.e., 13.75 solar mass per particle instead of 1375 solar mass. The Milky Way model has been constructed following (Barnes et al 2002), and it includes a bulge, an exponential stellar disc, and a core dark matter halo, while the Sgr dwarf galaxy is made of a dark matter halo and a disc (see Table 1).…”

“…The halo density profile is converging at large radii. More details about the modeling components could be found in Barnes et al (2002) and in Wang et al (2022). The modeling is realized using GIZMO (Hopkins et al 2015) and Table 1 gives the initial conditions.…”

“…Since this ongoing minor merger event was discovered by Ibata et al (1994), Sagittarius core or remnant has been investigated by many studies (Ibata et al 1995;Lokas et al 2010;Penarrubia et al 2010;Vasiliev et al 2020Vasiliev et al , 2021del Pino et al 2021). This dwarf galaxy may probe the Milky Way potential and may have shaped the Milky Way disc (Antoja et al 2018;Wang et al 2018aWang et al ,b, 2019Wang et al , 2020aLópez-Corredoira et al 2020;Yu et al 2021;Bland-Hawthorn et al 2021;Yang et al 2022). There are also globular clusters associated to the Sgr system such as M 54, Ter 8, Ter 7, Arp 2 inside or near the main body of the Sagittarius dwarf spheroidal galaxy, and Pal 12, Whiting 1 that belong to the trailing arm (Bellazzini et al 2020).Together with the Sgr stream, they provide us many tests on the role of the dark matter in a nearby galaxy.…”

“…Vasiliev et al (2020) showed that a tidally disrupted Sgr making 2.5 orbits around the Milky Way could reproduce many of the stream observational properties, for which they found a present-day core mass of 4.0 × 10 8 M within a 5 kpc radius, and for which they assumed a total MW mass of 9 × 10 11 M . Recently, Wang et al (2022) considered a Milky Way mass of 5.2 × 10 11 M and an initial Sgr mass of 9.3 × 10 8 M in an N-body simulation model, resulting into a Sgr core mass of 3.1 × 10 7 M within a 2 kpc radius. They have also been able to reproduce as well 3D spatial features of Sgr stream, including its leading and trailing arms, and noticeably, the observed bifurcations.…”