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The Extremely Metal-rich Knot of Stars at the Heart of the Galaxy

Rix, Hans Walter ; Chandra, Vedant ; Zasowski, Gail ; Pillepich, Annalisa ; Khoperskov, Sergey ; Feltzing, Sofia LU orcid ; Wyse, Rosemary F.G. ; Frankel, Neige ; Horta, Danny and Kollmeier, Juna , et al. (2024) In Astrophysical Journal 975(2).
Abstract

We show with Gaia XP spectroscopy that extremely metal-rich (EMR) stars in the Milky Way ([M/H]XP ≳ 0.5) are largely confined to a tight "knot"at the center of the Galaxy. This EMR knot is round in projection, has a fairly abrupt edge near RGC,proj ∼ 1.5 kpc, and is a dynamically hot system. This central knot also contains very metalrich (VMR; +0.2 . [M/H]XP . +0.4) stars. However, in contrast to EMR stars, the bulk of VMR stars forms an extended, highly flattened distribution in the inner Galaxy (RGC ≲5 kpc). We draw on TNG50 simulations of Milky Way analogs for context and find that compact, metal-rich knots confined to ≲1.5 kpc are a universal feature. In typical simulated analogs, the top 5%-10% most metal-rich stars are confined to... (More)

We show with Gaia XP spectroscopy that extremely metal-rich (EMR) stars in the Milky Way ([M/H]XP ≳ 0.5) are largely confined to a tight "knot"at the center of the Galaxy. This EMR knot is round in projection, has a fairly abrupt edge near RGC,proj ∼ 1.5 kpc, and is a dynamically hot system. This central knot also contains very metalrich (VMR; +0.2 . [M/H]XP . +0.4) stars. However, in contrast to EMR stars, the bulk of VMR stars forms an extended, highly flattened distribution in the inner Galaxy (RGC ≲5 kpc). We draw on TNG50 simulations of Milky Way analogs for context and find that compact, metal-rich knots confined to ≲1.5 kpc are a universal feature. In typical simulated analogs, the top 5%-10% most metal-rich stars are confined to a central knot; however, in our Milky Way data this fraction is only 0.1%. Dust-penetrating wide-area near-infrared spectroscopy, such as the fifth Sloan Digital Sky Survey, will be needed for a rigorous estimate of the fraction of stars in the Galactic EMR knot. Why in our Milky Way only EMR giants are confined to such a central knot remains to be explained. Remarkably, the central few kiloparsecs of the Milky Way harbor both the highest concentration of metal-poor stars (the "poor old heart") and almost all EMR stars. This highlights the stellar population diversity at the bottom of galactic potential wells.

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organization
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type
Contribution to journal
publication status
published
subject
keywords
Gaia (2360), Galaxy chemical evolution (580), Galaxy evolution (594), Metallicity (1031), Milky Way dynamics (1051), Milky Way evolution (1052), Milky Way formation (1053)
in
Astrophysical Journal
volume
975
issue
2
article number
293
publisher
American Astronomical Society
external identifiers
  • scopus:85209572347
ISSN
0004-637X
DOI
10.3847/1538-4357/ad7aee
project
Galactic Time Machine
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2024. The Author(s).
id
4309d7f1-f6a0-411e-932b-0238b35f1185
date added to LUP
2024-11-27 15:45:07
date last changed
2025-04-04 15:23:38
@article{4309d7f1-f6a0-411e-932b-0238b35f1185,
  abstract     = {{<p>We show with Gaia XP spectroscopy that extremely metal-rich (EMR) stars in the Milky Way ([M/H]XP ≳ 0.5) are largely confined to a tight "knot"at the center of the Galaxy. This EMR knot is round in projection, has a fairly abrupt edge near RGC,proj ∼ 1.5 kpc, and is a dynamically hot system. This central knot also contains very metalrich (VMR; +0.2 . [M/H]XP . +0.4) stars. However, in contrast to EMR stars, the bulk of VMR stars forms an extended, highly flattened distribution in the inner Galaxy (RGC ≲5 kpc). We draw on TNG50 simulations of Milky Way analogs for context and find that compact, metal-rich knots confined to ≲1.5 kpc are a universal feature. In typical simulated analogs, the top 5%-10% most metal-rich stars are confined to a central knot; however, in our Milky Way data this fraction is only 0.1%. Dust-penetrating wide-area near-infrared spectroscopy, such as the fifth Sloan Digital Sky Survey, will be needed for a rigorous estimate of the fraction of stars in the Galactic EMR knot. Why in our Milky Way only EMR giants are confined to such a central knot remains to be explained. Remarkably, the central few kiloparsecs of the Milky Way harbor both the highest concentration of metal-poor stars (the "poor old heart") and almost all EMR stars. This highlights the stellar population diversity at the bottom of galactic potential wells.</p>}},
  author       = {{Rix, Hans Walter and Chandra, Vedant and Zasowski, Gail and Pillepich, Annalisa and Khoperskov, Sergey and Feltzing, Sofia and Wyse, Rosemary F.G. and Frankel, Neige and Horta, Danny and Kollmeier, Juna and Stassun, Keivan and Ness, Melissa K. and Bird, Jonathan C. and Nidever, David and Fernández-Trincado, José G. and Amarante, João A.S. and Laporte, Chervin F.P. and Lian, Jianhui}},
  issn         = {{0004-637X}},
  keywords     = {{Gaia (2360); Galaxy chemical evolution (580); Galaxy evolution (594); Metallicity (1031); Milky Way dynamics (1051); Milky Way evolution (1052); Milky Way formation (1053)}},
  language     = {{eng}},
  month        = {{11}},
  number       = {{2}},
  publisher    = {{American Astronomical Society}},
  series       = {{Astrophysical Journal}},
  title        = {{The Extremely Metal-rich Knot of Stars at the Heart of the Galaxy}},
  url          = {{http://dx.doi.org/10.3847/1538-4357/ad7aee}},
  doi          = {{10.3847/1538-4357/ad7aee}},
  volume       = {{975}},
  year         = {{2024}},
}