Zhen Yuan, Tadafumi Matsuno, Tatyana Sitnova, Nicolas F. Martin, Rodrigo A. Ibata

| Summary:

[[{“value”:”The discovery of the most metal-poor stream, C-19, provides us with a fossil
record of a stellar structure born very soon after the Big Bang. In this work,
we search for new C-19 members over the whole sky by combining two
complementary stream-searching algorithms, STREAMFINDER and StarGO,, and
utilizing low-metallicity star samples from the Pristine survey as well as Gaia
BP/RP spectro-photometric catalogues. We confirm twelve new members, spread
over more than 100$^circ$, using velocity and metallicity information from a
set of spectroscopic follow-up programs that targeted a quasi-complete sample
of our bright candidates ($G lesssim 16.0$). From the updated set of stream
members, we confirm that the stream is wide, with a stream width of $sim200$
pc, and dynamically hot, with a derived velocity dispersion of
$11.1^{+1.9}_{-1.6}$ km/s. The tension remains between these quantities and a
purely baryonic scenario in which the relatively low-mass stream (even updated
to a few $10^4M_{odot}$) stems from a globular cluster progenitor, as
suggested by its chemical abundances. Some heating mechanism, such as
preheating of the cluster in its own dark matter halo or through interactions
with halo sub-structures appears necessary to explain the tension. The impact
of binaries on the measured dispersion also remains unknown. Detailed elemental
abundances of more stream members as well as multi-epoch radial velocities from
spectroscopic observations are therefore crucial to fully understand the nature
and past history of the most metal-poor stream of the Milky Way.”}]] 

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