Kavli Affiliate: Andrey Kravtsov
| First 5 Authors: Sarah G. Kane, Sarah G. Kane, , ,
| Summary:
As sites of some of the most efficient star formation in the Universe,
globular clusters (GCs) have long been hypothesized to be the building blocks
of young galaxies. Within the Milky Way, our best tracers of the contribution
of GCs to the proto-Galaxy are stars with such anomalous overabundance in
nitrogen and depletion in oxygen ("high-[N/O] stars") that they can be
identified as having originated in a cluster long after they have escaped. We
identify associations between these high-[N/O] field stars and GCs using
integrals of motion and metallicities and compare to chemically typical halo
stars to quantify any excess association, enabling a population-level
exploration of the formation sites of the nitrogen-enhanced stars in the field.
Relative to the halo as a whole, high-[N/O] stars show stronger associations
with the most initially massive, inner Galaxy GCs, suggesting that many
nitrogen-rich stars formed in these environments. However, when compared to a
sample matched in orbital energy, the excess largely disappears: high-[N/O]
stars are, on average, no more associated with surviving GCs than
energy-matched halo stars, despite their [N/O] abundances indicating GC
origins, consistent with a scenario in which a substantial fraction of
low-energy inner-halo stars originate in GCs, so an energy-matched control
dilutes any differential excess. We argue that associations between high-[N/O]
stars and their parent GCs are further weakened because dynamical friction and
the Galactic bar have altered integrals of motion, limiting the reliability of
precise present-day associations and, especially, individual star-to-cluster
tagging.
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