Evidence for the Typhon Stellar Stream as the Remnant of a Recently-disrupted Dwarf Galaxy
Abstract
In the hierarchical model of galaxy formation, the Milky Way's stellar halo assembles through the successive accretion of dwarf galaxies. While many resulting substructures have been identified, the origin of the recently discovered Typhon stellar stream remains ambiguous, as dynamical data alone are insufficient to distinguish between a globular cluster and a dwarf galaxy progenitor. To resolve this, we combine astrometry from Gaia with spectroscopic data from available surveys to comprehensively analyze the stream's chemical and dynamical properties. We identify 107 candidate members, significantly expanding the known sample. Three of these candidates lie beyond 55 kpc, with the farthest at 67 kpc, lending further support to Typhon's inferred large apocentric distance. Our analysis yields a mean metallicity of [Fe/H]=−1.42±0.07 and a metallicity dispersion of σ[Fe/H] = 0.26+0.06−0.05 dex. This metallicity dispersion supports a dwarf-galaxy origin for the Typhon stream. Typhon's high orbital energy is consistent with a relatively recent accretion of a fully disrupted dwarf galaxy with a stellar mass in the range of 106 M⊙ < M⋆ ≲ 107 M⊙. Furthermore, Typhon is the only major dwarf-galaxy stellar stream in the Milky Way's halo to exhibit such an extreme orbital eccentricity of e ≳ 0.85. We conjecture that dwarf-galaxy streams from high-eccentricity mergers are fully dissolved much more rapidly than those on circular orbits, in line with Typhon's proposed recent accretion. Additional dwarf-galaxy stellar streams on high-eccentricity orbits should be discoverable with next-generation photometric surveys as well as future releases from the Gaia space mission.
Related
- Evidence for a nova super-remnant surrounding the recurrent nova V745 Scorpii using eROSITA
- Infrared Cavity Surrounding T Pyxidis: Evidence of a Nova Super-remnant?
- Evidence for a nova super-remnant surrounding the recurrent nova V745 Scorpii using eROSITA
- A steadily declining dispersion measure for the repeating fast radio burst FRB 20220529A: Evidence for an FRB engine embedded in an expanding supernova remnant
- Investigating the Young Stellar Populations and Hierarchies in Nearby Galaxies with the UVIT. III. Evidence for a Largest Scale of Correlated Stellar Structures and a Non-universal Fractal Dimension
BibTeX
@misc{nogueirasantos2026evidence,
title = {{Evidence for the Typhon Stellar Stream as the Remnant of a Recently-disrupted Dwarf Galaxy}},
author = {João V. Nogueira-Santos and Guilherme Limberg and Silvia Rossi and Hélio D. Perottoni and Lais Borbolato and Fabrícia O. Barbosa and André R. da Silva},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.30615},
eprint = {2609.30615},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.30615},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Evidence for the Typhon Stellar Stream as the Remnant of a Recently-disrupted Dwarf Galaxy
AU - João V. Nogueira-Santos
AU - Guilherme Limberg
AU - Silvia Rossi
AU - Hélio D. Perottoni
AU - Lais Borbolato
AU - Fabrícia O. Barbosa
AU - André R. da Silva
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.30615
UR - https://arxiv.org/abs/2609.30615
AB - In the hierarchical model of galaxy formation, the Milky Way's stellar halo assembles through the successive accretion of dwarf galaxies. While many resulting substructures have been identified, the origin of the recently discovered Typhon stellar stream remains ambiguous, as dynamical data alone are insufficient to distinguish between a globular cluster and a dwarf galaxy progenitor. To resolve this, we combine astrometry from Gaia with spectroscopic data from available surveys to comprehensively analyze the stream's chemical and dynamical properties. We identify 107 candidate members, significantly expanding the known sample. Three of these candidates lie beyond 55 kpc, with the farthest at 67 kpc, lending further support to Typhon's inferred large apocentric distance. Our analysis yields a mean metallicity of [Fe/H]=−1.42±0.07 and a metallicity dispersion of σ_[Fe/H] = 0.26^+0.06_−0.05 dex. This metallicity dispersion supports a dwarf-galaxy origin for the Typhon stream. Typhon's high orbital energy is consistent with a relatively recent accretion of a fully disrupted dwarf galaxy with a stellar mass in the range of 10^6 M_⊙ < M_⋆ ≲ 10^7 M_⊙. Furthermore, Typhon is the only major dwarf-galaxy stellar stream in the Milky Way's halo to exhibit such an extreme orbital eccentricity of e ≳ 0.85. We conjecture that dwarf-galaxy streams from high-eccentricity mergers are fully dissolved much more rapidly than those on circular orbits, in line with Typhon's proposed recent accretion. Additional dwarf-galaxy stellar streams on high-eccentricity orbits should be discoverable with next-generation photometric surveys as well as future releases from the Gaia space mission.
ER -