TY - JOUR
T1 - The Extremely Metal-rich Knot of Stars at the Heart of the Galaxy
AU - Rix, Hans Walter
AU - Chandra, Vedant
AU - Zasowski, Gail
AU - Pillepich, Annalisa
AU - Khoperskov, Sergey
AU - Feltzing, Sofia
AU - Wyse, Rosemary F.G.
AU - Frankel, Neige
AU - Horta, Danny
AU - Kollmeier, Juna
AU - Stassun, Keivan
AU - Ness, Melissa K.
AU - Bird, Jonathan C.
AU - Nidever, David
AU - Fernández-Trincado, José G.
AU - Amarante, João A.S.
AU - Laporte, Chervin F.P.
AU - Lian, Jianhui
N1 - Publisher Copyright:
© 2024. The Author(s).
PY - 2024/11/1
Y1 - 2024/11/1
N2 - 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.
AB - 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.
KW - Gaia (2360)
KW - Galaxy chemical evolution (580)
KW - Galaxy evolution (594)
KW - Metallicity (1031)
KW - Milky Way dynamics (1051)
KW - Milky Way evolution (1052)
KW - Milky Way formation (1053)
U2 - 10.3847/1538-4357/ad7aee
DO - 10.3847/1538-4357/ad7aee
M3 - Article
AN - SCOPUS:85209572347
SN - 0004-637X
VL - 975
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 293
ER -