DESI Data Reveals New Details About Local Group Dwarf Galaxy Kinematics and Composition
Researchers used the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1) to confirm stellar membership in 15 Local Group dwarf galaxies by combining radial velocity measurements with Gaia proper motion and photometry data. The study provides the first systemic radial velocity measurement for DES J0225+0304 and traces the stellar kinematics of the Sextans dwarf galaxy out to roughly 10 half-light radii. The findings offer new evidence for distinct stellar populations within Sextans and hint at an 'outside-in' star formation history or an ex-situ stellar halo.
Using DESI DR1 radial velocity data cross-matched with Gaia-based candidate member lists, the study securely confirmed stellar membership in 15 Local Group dwarf galaxies, validating the effectiveness of Gaia proper motion and photometry selection algorithms in reducing foreground contamination. For the faint system DES J0225+0304, two associated stars yielded the first-ever systemic radial velocity measurement of −150.0 ± 7.0 km/s. Draco and Sextans had the highest confirmed member counts, with Sextans receiving particular focus: DESI data traced its stellar kinematics to unprecedented radii of up to ~10 half-light radii. The analysis revealed that metal-poor stars in Sextans show higher velocity dispersion and are spatially more extended, while metal-rich stars are kinematically colder and centrally concentrated, with a steep inner metallicity gradient (~−0.36 dex/kpc) that flattens in the outer regions. The study also identified 8 ultra metal-poor ([Fe/H] < −4) stellar candidates requiring higher signal-to-noise follow-up observations, and cautions that DESI abundance measurements for very metal-poor stars ([Fe/H] ≲ −2.0) show large scatter and an anti-correlation with metallicity, limiting their reliability in that regime.
What's missing
The study notes that DESI [α/Fe] abundance ratios for very metal-poor stars ([Fe/H] ≲ −2.0) show anomalous scatter and anti-correlation with metallicity, but does not fully characterize the systematic or instrumental origin of this effect. The physical mechanism driving the apparent 'outside-in' star formation or ex-situ halo in Sextans remains unresolved and is not directly tested. Confirmation of the 8 ultra metal-poor candidates awaits higher signal-to-noise spectroscopy.
What different sources said
- arXiv astro-phCenter
Confirming membership in Local Group galaxies with the Dark Energy Spectroscopic Instrument Data Release 1
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