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Title: Nitrogen enrichment and clustered star formation at the dawn of the Galaxy
ABSTRACT Anomalously high nitrogen-to-oxygen abundance ratios [N/O] are observed in globular clusters (GCs), among the field stars of the Milky Way (MW), and even in the gas in a z ≈ 11 galaxy. Using data from the APOGEE Data Release 17 and the Gaia Data Release 3, we present several independent lines of evidence that most of the MW’s high-[N/O] stars were born in situ in massive bound clusters during the early, pre-disc evolution of the Galaxy. Specifically, we show that distributions of metallicity [Fe/H], energy, the angular momentum Lz, and distance of the low-metallicity high-[N/O] stars match the corresponding distributions of stars of the Aurora population and of the in situ GCs. We also show that the fraction of in situ field high-[N/O] stars, fN/O, increases rapidly with decreasing metallicity. During epochs when metallicity evolves from $$\rm [Fe/H]=-1.5$$ to $$\rm [Fe/H]=-0.9$$, the Galaxy spins up and transitions from a turbulent Aurora state to a coherently rotating disc. This transformation is accompanied by many qualitative changes. In particular, we show that high N/O abundances similar to those observed in GN-z11 were common before the spin-up ($$\rm [Fe/H]\lesssim -1.5$$) when up to $$\approx 50~{{\ \rm per\ cent}}-70~{{\ \rm per\ cent}}$$ of the in situ stars formed in massive bound clusters. The dramatic drop of fN/O at $$\rm [Fe/H]\gtrsim -0.9$$ indicates that after the disc emerges the fraction of stars forming in massive bound clusters decreases by two orders of magnitude.  more » « less
Award ID(s):
1911111
PAR ID:
10459399
Author(s) / Creator(s):
;
Publisher / Repository:
Oxford University Press
Date Published:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
525
Issue:
3
ISSN:
0035-8711
Format(s):
Medium: X Size: p. 4456-4473
Size(s):
p. 4456-4473
Sponsoring Org:
National Science Foundation
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