Kavli Affiliate: Risa H. Wechsler
| First 5 Authors: Christian Aganze, Vedant Chandra, Risa H. Wechsler, Ting S. Li, Sergey E. Koposov
| Summary:
The census of stellar streams and dwarf galaxies in the Milky Way provides
direct constraints on galaxy formation models and the nature of dark matter.
The DESI Milky Way survey (with a footprint of 14,000$~deg{^2}$ and a depth of
$r<19$ mag) delivers the largest sample of distant metal-poor stars compared to
previous optical fiber-fed spectroscopic surveys. This makes DESI an ideal
survey to search for previously undetected streams and dwarf galaxies. We
present a detailed characterization of the Cocytos stream, which was
re-discovered using a clustering analysis with a catalog of giants in the DESI
year 3 data, supplemented with Magellan/MagE spectroscopy. Our analysis reveals
a relatively metal-rich ([Fe/H]$=-1.3$) and thick stream (width$=1.5^circ$) at
a heliocentric distance of $approx 25$ kpc, with an internal velocity
dispersion of 6.5-9 km s$^{-1}$. The stream’s metallicity, radial orbit, and
proximity to the Virgo stellar overdensities suggest that it is most likely a
disrupted globular cluster that came in with the Gaia-Enceladus merger. We also
confirm its association with the Pyxis globular cluster. Our result showcases
the ability of wide-field spectroscopic surveys to kinematically discover faint
disrupted dwarfs and clusters, enabling constraints on the dark matter
distribution in the Milky Way.
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