Abstract While the Milky Way nuclear star cluster (MW NSC) has been studied extensively, how it formed is uncertain. Studies have shown it contains a solar and supersolar metallicity population that may have formed in situ, along with a subsolar-metallicity population that may have formed via mergers of globular clusters and dwarf galaxies. Stellar abundance measurements are critical to differentiate between formation scenarios. We present new measurements of [M/H] and α -element abundances [ α /Fe] of two subsolar-metallicity stars in the Galactic center. These observations were taken with the adaptive-optics-assisted high-resolution ( R = 24,000) spectrograph NIRSPEC in the K band (1.8–2.6 micron). These are the first α -element abundance measurements of subsolar-metallicity stars in the MW NSC. We measure [M/H] = − 0.59 ± 0.11, [ α /Fe] = 0.05 ± 0.15 and [M/H] = − 0.81 ± 0.12, [ α /Fe] = 0.15 ± 0.16 for the two stars at the Galactic center; the uncertainties are dominated by systematic uncertainties in the spectral templates. The stars have an [ α /Fe] in between the [ α /Fe] of globular clusters and dwarf galaxies at similar [M/H] values. Their abundances are very different than the bulk of the stars in the nuclear star cluster. These results indicate that the subsolar-metallicity population in the MW NSC likely originated from infalling dwarf galaxies or globular clusters and are unlikely to have formed in situ.
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Stellar populations in the transition region of nuclear star cluster and nuclear stellar disc
The Milky Way nuclear star cluster (NSC) is located within the nuclear stellar disc (NSD) in the Galactic Centre. It is not fully understood if the formation and evolution of these two components are connected, and how they influence each other. We study the stellar populations in the transition region of NSC and NSD. We observed two ∼4.3 pc2 fields with the integral-field spectrograph KMOS (VLT), located at r ∼ 20 pc (>4 Re) to the Galactic East and West of the NSC. We extract and analyse medium-resolution stellar spectra of >200 stars per field. The data contain in total nine young star candidates. We use stellar photometry to estimate the stellar masses, effective temperatures, and spectral types of the young stars. The stars are consistent with an age of 4–6 Myr, they may have formed inside the Quintuplet cluster, but were dispersed in dynamical interactions. Most stars in the two fields are red giant stars, and we measure their stellar metallicities [M/H] using full spectral fitting. We compare our [M/H] distributions to the NSC and NSD, using data from the literature, and find that the overall metallicity decreases from the central NSC, over the transition region, to the NSD. The steep decrease of [M/H] from the NSC to the region dominated by the NSD indicates that the two components have distinct stellar populations and formation histories.
more » « less- NSF-PAR ID:
- 10381831
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 513
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 5920-5934
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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