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

Hans Walter Rix, Vedant Chandra, Gail Zasowski, Annalisa Pillepich, Sergey Khoperskov, Sofia Feltzing, Rosemary F.G. Wyse, Neige Frankel, Danny Horta, Juna Kollmeier, Keivan Stassun, Melissa K. Ness, Jonathan C. Bird, David Nidever, José G. Fernández-Trincado, João A.S. Amarante, Chervin F.P. Laporte, Jianhui Lian

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskriftPeer review

Sammanfattning

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.

Originalspråkengelska
Artikelnummer293
TidskriftAstrophysical Journal
Volym975
Nummer2
DOI
StatusPublished - 2024 nov. 1

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Publisher Copyright:
© 2024. The Author(s).

Ämnesklassifikation (UKÄ)

  • Astronomi, astrofysik och kosmologi

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