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Peer-reviewedCC BY 4.0The Astrophysical Journal

Potamides: Mapping Dark Matter Halo Shapes from Stellar Stream Tracks in the Local Universe

  • Sirui Wu1
  • Nathaniel Starkman2,3
  • Sarah Pearson1,4
  • Jacob Nibauer5
  • Juan Miró-Carretero6,7
  • David Martínez-Delgado8,9
9 affiliations
  1. 1University of Copenhagen
  2. 2Massachusetts Institute of Technology
  3. 3Case Western Reserve University
  4. 4Technical University of Denmark
  5. 5Princeton University
  6. 6Universidad Complutense de Madrid
  7. 7Leiden University
  8. 8Centro de Estudios de Física del Cosmos de Aragón (CEFCA)
  9. 9ARAID Foundation
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Abstract

Stellar streams trace the gravitational potential of their host galaxies and offer a direct probe of dark matter halo geometry. Cosmological simulations predict that halo shapes depend on both baryonic physics and the nature of dark matter, yet observational constraints on halo flattening and orientation remain limited, especially for individual galaxies. We present potamides ( https://potamides.readthedocs.io ), which utilizes the curvature of extragalactic stellar streams to derive constraints on halo shapes. We apply potamides to 15 stellar streams from the Stellar Stream Legacy Survey to infer the projected axis ratios and orientation of their host halos. We find that some streams in our sample exclude large regions of halo flattenings and halo orientations. Systems with edge-on wrapping loops or sharp turning points yield the strongest constraints, whereas great circle-like streams remain largely uninformative. All streams in our sample support a spherical halo for a given flattening direction. These results demonstrate that stream morphology can provide halo shape constraints for individual external galaxies. With upcoming surveys (such as Euclid, Rubin, Roman, and ARRAKIHS) expected to discover large numbers of stellar streams, this curvature-based technique will enable rapid statistical tests of dark matter and baryonic physics through the shapes and alignments of halos and disks across cosmic time.

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Cite

BibTeXRIS
BibTeX
@article{wu2026potamides,
  title = {{Potamides: Mapping Dark Matter Halo Shapes from Stellar Stream Tracks in the Local Universe}},
  author = {Sirui Wu and Nathaniel Starkman and Sarah Pearson and Jacob Nibauer and Juan Miró-Carretero and David Martínez-Delgado},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea0d4},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea0d4},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Potamides: Mapping Dark Matter Halo Shapes from Stellar Stream Tracks in the Local Universe
AU  - Sirui Wu
AU  - Nathaniel Starkman
AU  - Sarah Pearson
AU  - Jacob Nibauer
AU  - Juan Miró-Carretero
AU  - David Martínez-Delgado
PY  - 2026
DA  - 2026/10/12
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea0d4
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea0d4
AB  - Stellar streams trace the gravitational potential of their host galaxies and offer a direct probe of dark matter halo geometry. Cosmological simulations predict that halo shapes depend on both baryonic physics and the nature of dark matter, yet observational constraints on halo flattening and orientation remain limited, especially for individual galaxies. We present potamides ( https://potamides.readthedocs.io ), which utilizes the curvature of extragalactic stellar streams to derive constraints on halo shapes. We apply potamides to 15 stellar streams from the Stellar Stream Legacy Survey to infer the projected axis ratios and orientation of their host halos. We find that some streams in our sample exclude large regions of halo flattenings and halo orientations. Systems with edge-on wrapping loops or sharp turning points yield the strongest constraints, whereas great circle-like streams remain largely uninformative. All streams in our sample support a spherical halo for a given flattening direction. These results demonstrate that stream morphology can provide halo shape constraints for individual external galaxies. With upcoming surveys (such as Euclid, Rubin, Roman, and ARRAKIHS) expected to discover large numbers of stellar streams, this curvature-based technique will enable rapid statistical tests of dark matter and baryonic physics through the shapes and alignments of halos and disks across cosmic time.
SN  - 0004-637X
SN  - 1538-4357
ER  -