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The Metallicity Gradient and Complex Formation History of the Outermost Halo of the Milky Way.
- Source :
- Astrophysical Journal; May2020, Vol. 894 Issue 1, p1-10, 10p
- Publication Year :
- 2020
-
Abstract
- We present an examination of the metallicity distribution function of the outermost stellar halo of the Galaxy based on an analysis of both local (within 4 kpc of the Sun, ∼16,500 stars) and non-local (∼21,700 stars) samples. These samples were compiled using spectroscopic metallicities from the Sloan Digital Sky Survey and photometric metallicities from the SkyMapper Southern Survey. We detect a negative metallicity gradient in the outermost halo (r > 35 kpc from the Galactic center), and find that the frequency of very metal-poor ([Fe/H] < −2.0) stars in the outer-halo region reaches up to ∼60% in our most distant sample, commensurate with previous theoretical predictions. This result provides clear evidence that the outer-halo formed hierarchically. The retrograde stars in the outermost halo exhibit a roughly constant metallicity, which may be linked to the accretion of the Sequoia progenitor. In contrast, prograde stars in the outermost halo exhibit a strong metallicity-distance dependence, indicating that they likely originated from the accretion of galaxies less massive than the Sequoia progenitor galaxy. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 0004637X
- Volume :
- 894
- Issue :
- 1
- Database :
- Complementary Index
- Journal :
- Astrophysical Journal
- Publication Type :
- Academic Journal
- Accession number :
- 143141921
- Full Text :
- https://doi.org/10.3847/1538-4357/ab7fa4