Kavli Affiliate: Anna Frebel
| First 5 Authors: Xiaowei Ou, Alexander Yelland, Anirudh Chiti, Anna Frebel, Guilherme Limberg
| Summary:
Dwarf galaxies like Sagittarius (Sgr) provide a unique window into the early
stages of galactic chemical evolution, particularly through their metal-poor
stars. By studying the chemical abundances of stars in the Sgr core and tidal
streams, we can gain insights into the assembly history of this galaxy and its
early heavy element nucleosynthesis processes. We efficiently selected
extremely metal-poor candidates in the core and streams for high-resolution
spectroscopic analysis using metallicity-sensitive photometry from SkyMapper
DR2, and Gaia DR3 XP spectra and proper motions. This allowed us to obtain a
high-purity selection of Sgr members based on stellar kinematics while reducing
the chances of potential contamination from the Milky Way halo. We present a
sample of 37 Sgr stars with detailed chemical abundances, of which we identify
10 extremely metal-poor (EMP; $rm{[Fe/H]} le -3.0$) stars, 25 very metal-poor
(VMP; $rm{[Fe/H]} le -2.0$) stars, and 2 metal-poor (MP; $rm{[Fe/H]} le
-1.0$) stars. This sample increases the number of extremely metal-poor Sgr
stars analyzed with high-resolution spectroscopy by a factor of five. Of these
stars, 15 are identified as members of the Sgr tidal stream, while the
remaining 22 are associated with the core. We derive abundances for up to 20
elements and identify no statistically significant differences between the
element abundance patterns across the core and stream samples. Intriguingly, we
identify stars that may have formed in ultra-faint dwarf galaxies that accreted
onto Sgr, in addition to patterns of C and r-process elements distinct from the
Milky Way halo. Over half of the sample shows a neutron-capture element
abundance pattern consistent with the scaled solar pure r-process pattern,
indicating early r-process enrichment in the Sgr progenitor.
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