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A Blueprint for the Milky Way's Stellar Populations. III. Spatial Distributions and Population Fractions of Local Halo Stars

Title
A Blueprint for the Milky Way's Stellar Populations. III. Spatial Distributions and Population Fractions of Local Halo Stars
Authors
An, DeokkeunBeers, Timothy C.
Ewha Authors
안덕근
SCOPUS Author ID
안덕근scopus
Issue Date
2021
Journal Title
ASTROPHYSICAL JOURNAL
ISSN
0004-637XJCR Link

1538-4357JCR Link
Citation
ASTROPHYSICAL JOURNAL vol. 918, no. 2
Publisher
IOP PUBLISHING LTD
Indexed
SCIE; SCOPUS WOS scopus
Document Type
Article
Abstract
We analyze the observed spatial, chemical and dynamical distributions of local metal-poor stars, based on photometrically derived metallicity and distance estimates along with proper motions from the Gaia mission. Along the Galactic prime meridian, we identify stellar populations with distinct properties in the metallicity versus rotational velocity space, including Gaia Sausage/Enceladus (GSE), the metal-weak thick disk (MWTD), and the Splash (sometimes referred to as the "in situ" halo). We model the observed phase-space distributions using Gaussian mixtures and refine their positions and fractional contributions as a function of distances from the Galactic plane (vertical bar Z vertical bar) and the Galactic center (R-GC), providing a global perspective of the major stellar populations in the local halo. Within the sample volume (divide vertical bar Z vertical bar < 6 kpc), stars associated with GSE exhibit a larger proportion of metal-poor stars at greater R-GC (Delta < Fe/H >/Delta R-GC = -0.05 +/- 0.02 dex kpc(-1)). This observed trend, along with a mild anticorrelation of the mean rotational velocity with metallicity (Delta < v(phi)>/Delta < Fe/H >similar to-10 km s(-1)dex(-1)), implies that more metal-rich stars in the inner region of the GSE progenitor were gradually stripped away, while the prograde orbit of the merger at infall became radialized by dynamical friction. The metal-rich GSE stars are causally disconnected from the Splash structure, whose stars are mostly found on prograde orbits (greater than or similar to 94%) and exhibit a more centrally concentrated distribution than GSE. The MWTD exhibits a similar spatial distribution to the Splash, suggesting earlier dynamical heating of stars in the primordial disk of the Milky Way, possibly before the GSE merger.
DOI
10.3847/1538-4357/ac07a4
Appears in Collections:
사범대학 > 과학교육과 > Journal papers
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