Tracing Kinematic and Chemical Properties of Sagittarius Stream by K-Giants, M-Giants, and BHB stars

Abstract

We characterize the kinematic and chemical properties of ∼3,000 Sagittarius (Sgr) stream stars, including K-giants, M-giants, and BHBs, select from SEGUE-2, LAMOST, and SDSS separately in Integrals-of-Motion space. The orbit of Sgr stream is quite clear from the velocity vector in X-Z plane. Stars traced by K-giants and M-giants present the apogalacticon of trailing steam is ∼ 100 kpc. The metallicity distributions of Sgr K-, M-giants, and BHBs present that the M-giants are on average the most metal-rich population, followed by K-giants and BHBs. All of the K-, M-giants, and BHBs indicate that the trailing arm is on average more metal-rich than leading arm, and the K-giants show that the Sgr debris is the most metal-poor part. The α-abundance of Sgr stars exhibits a similar trend with the Galactic halo stars at lower metallicity ([Fe/H] <∼ −1.0 dex), and then evolve down to lower [α/Fe] than disk stars at higher metallicity, which is close to the evolution pattern of α-element of Milky Way dwarf galaxies. We find V Y and metallicity of K-giants have gradients along the direction of line-of-sight from the Galactic center in X-Z plane, and the K-giants show that V Y increases with metallicity at [Fe/H] >∼ −1.5 dex. After dividing the Sgr stream into bright and faint stream according to their locations in equatorial coordinate, the K-giants and BHBs show that the bright and faint stream present different V Y and metallicities, the bright stream is on average higher in V Y and metallicity than the faint stream.

Identification of Sagittarius stream members in Angular Momentum space with Gaussian mixture techniques

“…1 and quantified in Table 1 via the hyperparameter σy. The large scatter of the orbital poles and Ly values may be related to the bifurcation of the leading & trailing tails (Yang et al 2019). The detection of old stream wraps provide new constraints to investiate the origin of the bifurcation in more detail.…”

“…In particular, we use Gaussian mixture techniques to quantify clustering in angular momentum space. Previous attempts to detect the Sgr stream using catalogues of halo stars with full phase-space coordinates either apply cuts in energy and/or angular momentum (Li et al 2019;Johnson et al 2020), or search for stars on similar orbits with Friends-of-Friends algorithms (Yang et al 2019). In contrast, our method draws statistical associations between objects in the halo without relying on assumptions on the form, shape or time-evolution of the MW potential, or introducing subjective cuts in integrals of motion.…”

Evidence from the H3 Survey That the Stellar Halo Is Entirely Comprised of Substructure

“…Before Gaia, studies made the best of incomplete phasespace data to select Sgr stream stars, typically relying on heuristics such as distance from the orbital plane (e.g., Newberg et al 2003;Belokurov et al 2014;Lancaster et al 2019). However, with full phase-space information, clean selections that fully exploit the highly coherent Sgr features are now possible (e.g., Li et al 2019;Yang et al 2019;Hayes et al 2020). Sgr is a high-energy, prograde overdensity in E-L z , and owing to its polar orbit, its angular momentum is concentrated in L y .…”

Overview of the LAMOST survey in the first decade

“…It can be traced more than 360 across the sky 166 and provides a unique window to explore the formation history of the MW. 167 Using data from LAMOST and other surveys (eg, SDSS, Gaia), a variety of types of stars has been used to trace the Sgr tidal debris, [168][169][170][171] revealing details about the structure of the stream and providing stronger constraints on the complex star formation history of the Sgr dSph.…”