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Peer-reviewedCC BY 4.0The Astrophysical Journal Letters

Rubin Observatory Reveals a Dust-shrouded Halo Globular Cluster in Ophiuchus

  • Aashay Pai1,2,3
  • William Cerny4
  • Andrew B. Pace5
  • Alex Drlica-Wagner1,2,6
  • Peter S. Ferguson7
  • Marla Geha4
  • Chin Yi Tan1,2
  • Sasha N. Campana8
  • Burçin Mutlu-Pakdil8
  • Alexander H. Riley9
  • Nora Shipp7
  • Guy S. Stringfellow10
10 affiliations
  1. 1University of Chicago
  2. 2NSF-Simons AI Institute for the Sky (SkAI)
  3. 3Université Grenoble Alpes
  4. 4Yale University
  5. 5University of Virginia
  6. 6Fermi National Accelerator Laboratory
  7. 7University of Washington
  8. 8Dartmouth College
  9. 9Lund University
  10. 10University of Colorado Boulder
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Abstract

We present the discovery of the Milky Way satellite Rubin-GC1 (Rubin J1628−1735) using data from the NSF-DOE Vera C. Rubin Observatory’s Early Data Preview 2. The system was discovered in the direction of the Galactic bulge with ( l , b ) ∼ (359°, 21°) in a region of high stellar density and a foreground reddening of E ( B − V ) ≈ 0.7. We simultaneously fit the morphology and isochrone parameters of Rubin-GC1, determining that it is a faint ( M V = − 2 . 4 − 0.7 + 0.5 ) and compact ( r 1 / 2 = 5 − 1 + 1 pc) Milky Way satellite at a distance of D ⊙ = 3 1 − 3 + 3 kpc; its stellar population is intermediate-age ( τ = 9 . 2 − 0.7 + 1.2 Gyr) and moderately metal-rich ( [ Fe / H ] iso = − 0.7 3 − 0.04 + 0.04 ). Together, these properties suggest Rubin-GC1 is most likely a star cluster in the faint tail of the luminosity function of globular clusters surrounding the Milky Way. We identify a distinct proper motion signature from Rubin-GC1 in Gaia DR3, and from a comparison of the system’s 5D phase space information to N -body models of the Sagittarius dwarf spheroidal galaxy’s tidal stream, we determine that Rubin-GC1 is likely an accreted cluster associated with the Sagittarius leading arm. The discovery of Rubin-GC1 highlights the potential of Rubin to uncover faint, resolved satellites in dust-shrouded regions of the Milky Way, including remnants of the accretion events that have shaped the Galaxy’s hierarchical assembly.

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Cite

BibTeXRIS
BibTeX
@article{pai2026rubin,
  title = {{Rubin Observatory Reveals a Dust-shrouded Halo Globular Cluster in Ophiuchus}},
  author = {Aashay Pai and William Cerny and Andrew B. Pace and Alex Drlica-Wagner and Peter S. Ferguson and Marla Geha and Chin Yi Tan and Sasha N. Campana and Burçin Mutlu-Pakdil and Alexander H. Riley and Nora Shipp and Guy S. Stringfellow},
  journal = {The Astrophysical Journal Letters},
  year = {2026},
  month = oct,
  doi = {10.3847/2041-8213/aeb122},
  url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeb122},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Rubin Observatory Reveals a Dust-shrouded Halo Globular Cluster in Ophiuchus
AU  - Aashay Pai
AU  - William Cerny
AU  - Andrew B. Pace
AU  - Alex Drlica-Wagner
AU  - Peter S. Ferguson
AU  - Marla Geha
AU  - Chin Yi Tan
AU  - Sasha N. Campana
AU  - Burçin Mutlu-Pakdil
AU  - Alexander H. Riley
AU  - Nora Shipp
AU  - Guy S. Stringfellow
PY  - 2026
DA  - 2026/10/28
JO  - The Astrophysical Journal Letters
DO  - 10.3847/2041-8213/aeb122
UR  - https://iopscience.iop.org/article/10.3847/2041-8213/aeb122
AB  - We present the discovery of the Milky Way satellite Rubin-GC1 (Rubin J1628−1735) using data from the NSF-DOE Vera C. Rubin Observatory’s Early Data Preview 2. The system was discovered in the direction of the Galactic bulge with ( l , b ) ∼ (359°, 21°) in a region of high stellar density and a foreground reddening of E ( B − V ) ≈ 0.7. We simultaneously fit the morphology and isochrone parameters of Rubin-GC1, determining that it is a faint ( M V = − 2 . 4 − 0.7 + 0.5 ) and compact ( r 1 / 2 = 5 − 1 + 1 pc) Milky Way satellite at a distance of D ⊙ = 3 1 − 3 + 3 kpc; its stellar population is intermediate-age ( τ = 9 . 2 − 0.7 + 1.2 Gyr) and moderately metal-rich ( [ Fe / H ] iso = − 0.7 3 − 0.04 + 0.04 ). Together, these properties suggest Rubin-GC1 is most likely a star cluster in the faint tail of the luminosity function of globular clusters surrounding the Milky Way. We identify a distinct proper motion signature from Rubin-GC1 in Gaia DR3, and from a comparison of the system’s 5D phase space information to N -body models of the Sagittarius dwarf spheroidal galaxy’s tidal stream, we determine that Rubin-GC1 is likely an accreted cluster associated with the Sagittarius leading arm. The discovery of Rubin-GC1 highlights the potential of Rubin to uncover faint, resolved satellites in dust-shrouded regions of the Milky Way, including remnants of the accretion events that have shaped the Galaxy’s hierarchical assembly.
SN  - 2041-8213
SN  - 2041-8205
ER  -