Chemical Abundances of the Typhon Stellar Stream

Abstract

We present the first high-resolution chemical abundances of seven stars in the recently discovered high-energy stream Typhon. Typhon stars have apocenters >100 kpc, making this the first detailed chemical picture of the Milky Way's very distant stellar halo. Though the sample size is limited, we find that Typhon's chemical abundances are more like a dwarf galaxy than a globular cluster, showing a metallicity dispersion and no presence of multiple stellar populations. Typhon stars display enhanced $\alpha$-element abundances and increasing r-process abundances with increasing metallicity. The high-$\alpha$ abundances suggest a short star formation duration for Typhon, but this is at odds with expectations for the distant Milky Way halo and the presence of delayed r-process enrichment. If the progenitor of Typhon is indeed a new dwarf galaxy, possible scenarios explaining this apparent contradiction include a dynamical interaction that increases Typhon's orbital energy, a burst of enhanced late-time star formation that raises [$\alpha$/Fe], and/or group preprocessing by another dwarf galaxy before infall into the Milky Way. Alternatively, Typhon could be the high-energy tail of a more massive disrupted dwarf galaxy that lost energy through dynamical friction. We cannot clearly identify a known low-energy progenitor of Typhon in the Milky Way, but 70% of high-apocenter stars in cosmological simulations are from high-energy tails of large dwarf galaxies. Typhon's surprising combination of kinematics and chemistry thus underscores the need to fully characterize the dynamical history and detailed abundances of known substructures before identifying the origin of new substructures.

12 pages, 4 figures, 2 tables, accepted to MNRAS

References in corpus (34)

• The Gaia mission
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• What is a globular cluster? An observational perspective
• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G=18.5
• A high resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy
• The Chemical Evolution of the Draco Dwarf Spheroidal Galaxy
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• The Global Dynamical Atlas of the Milky Way mergers: Constraints from Gaia EDR3 based orbits of globular clusters, stellar streams and satellite galaxies
• The Bizarre Chemical Inventory of NGC 2419, An Extreme Outer Halo Globular Cluster
• High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey
• A Synoptic Map of Halo Substructures from the Pan-STARRS1 3π Survey
• Multiple populations in globular clusters and their parent galaxies
• $S^5$: The Orbital and Chemical Properties of One Dozen Stellar Streams
• The Southern Stellar Stream Spectroscopic Survey (S5): Chemical Abundances of Seven Stellar Streams
• Orbital Clustering Identifies the Origins of Galactic Stellar Streams
• Elevated r-process enrichment in Gaia Sausage and Sequoia
• Detailed Abundances of Two Very Metal-Poor Stars in Dwarf Galaxies
• Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III
• Evidence from Disrupted Halo Dwarfs that $r$-process Enrichment via Neutron Star Mergers is Delayed by $\gtrsim 500$ Myrs
• The Populations of Carina. II. Chemical Enrichment
• The value-added catalogue for LAMOST DR8 low-resolution spectra
• The Pristine survey -- XVI. The metallicity of 26 stellar streams around the Milky Way detected with the STREAMFINDER in Gaia EDR3
• Enrichment in r-process elements from multiple distinct events in the early Draco dwarf spheroidal galaxy
• Simultaneous Constraints on the Star Formation History and Nucleosynthesis of Sculptor dSph
• Reconstructing the Accretion History of the Galactic Stellar Halo from Chemical Abundance Ratio Distributions
• High-precision chemical abundances of Galactic building blocks. II. Revisiting the chemical distinctness of the Helmi streams
• Abundance Patterns of $\alpha$ and Neutron-capture Elements in the Helmi Stream
• Reading the CARDs: the Imprint of Accretion History in the Chemical Abundances of the Milky Way's Stellar Halo
• Possibilities and Limitations of Kinematically Identifying Stars from Accreted Ultra-Faint Dwarf Galaxies
• What is the Milky Way outer halo made of? High resolution spectroscopy of distant red giants

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• Extending the Chemical Reach of the H3 Survey: Detailed Abundances of the Dwarf-galaxy Stellar Stream Wukong/LMS-1
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