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Peer-reviewedCC BY 4.0The Astrophysical Journal

The Flare and Spiral Structure of the Milky Way’s Disk as Traced by Young Giant Stars

  • E. Poggio1
  • R. Drimmel1
  • S. Khanna1
  • R. Andrae2,3
  • M. G. Lattanzi1
  1. 1INAF–Osservatorio Astrofisico di Torino
  2. 2Max Planck Institute for Astronomy,
  3. 3Deutsches Zentrum für Astrophysik
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Abstract

We explore the three-dimensional structure of a sample of ∼16,000 young giant stars in the Galactic disk out to ∼8 kpc in heliocentric distance. This population traces a thin disk with a local vertical scale height of h Z ⊙ = 74 ± 5 pc, which progressively thickens toward the outer Galaxy with a prominent Galactic flare, rising exponentially with a radial scale length of h fl = 3.5 ± 0.4 kpc. Our analysis incorporates both the survey selection function and the vertical displacements caused by the Galactic warp and corrugations, which, if neglected, would lead to significant biases in the derived disk scale height. In the Galactic plane, the young giants trace coherent spiral arm segments, extending previous maps based on upper main sequence (UMS) and OB stars by 2–4 kpc, depending on the considered direction. The obtained map supports a pitch angle of roughly 20° for the Perseus Arm, and shows that the Local/Orion Arm stretches at least 10 kpc in length. Unlike earlier and more local maps based on UMS and OB stars, where the relatively small sampled portion of the Perseus Arm appeared as a short, nearly straight feature, our map reveals it as an extended structure with a gentle curvature, as expected for spiral arms on large scales. In the inner Galaxy, we also identify a new segment likely associated with the Scutum Arm, clearly detached from the Sagittarius-Carina Arm in the fourth Galactic quadrant.

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Cite

BibTeXRIS
BibTeX
@article{poggio2026flare,
  title = {{The Flare and Spiral Structure of the Milky Way’s Disk as Traced by Young Giant Stars}},
  author = {E. Poggio and R. Drimmel and S. Khanna and R. Andrae and M. G. Lattanzi},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea55f},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea55f},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - The Flare and Spiral Structure of the Milky Way’s Disk as Traced by Young Giant Stars
AU  - E. Poggio
AU  - R. Drimmel
AU  - S. Khanna
AU  - R. Andrae
AU  - M. G. Lattanzi
PY  - 2026
DA  - 2026/10/14
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea55f
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea55f
AB  - We explore the three-dimensional structure of a sample of ∼16,000 young giant stars in the Galactic disk out to ∼8 kpc in heliocentric distance. This population traces a thin disk with a local vertical scale height of h Z ⊙ = 74 ± 5 pc, which progressively thickens toward the outer Galaxy with a prominent Galactic flare, rising exponentially with a radial scale length of h fl = 3.5 ± 0.4 kpc. Our analysis incorporates both the survey selection function and the vertical displacements caused by the Galactic warp and corrugations, which, if neglected, would lead to significant biases in the derived disk scale height. In the Galactic plane, the young giants trace coherent spiral arm segments, extending previous maps based on upper main sequence (UMS) and OB stars by 2–4 kpc, depending on the considered direction. The obtained map supports a pitch angle of roughly 20° for the Perseus Arm, and shows that the Local/Orion Arm stretches at least 10 kpc in length. Unlike earlier and more local maps based on UMS and OB stars, where the relatively small sampled portion of the Perseus Arm appeared as a short, nearly straight feature, our map reveals it as an extended structure with a gentle curvature, as expected for spiral arms on large scales. In the inner Galaxy, we also identify a new segment likely associated with the Scutum Arm, clearly detached from the Sagittarius-Carina Arm in the fourth Galactic quadrant.
SN  - 0004-637X
SN  - 1538-4357
ER  -