Swarming in stellar streams: Unveiling the structure of the Jhelum stream with ant colony-inspired computation
arxiv(2023)
摘要
The halo of the Milky Way galaxy hosts multiple dynamically coherent
substructures known as stellar streams that are remnants of tidally disrupted
systems such as globular clusters (GCs) and dwarf galaxies (DGs). A particular
case is that of the Jhelum stream, which is known for its complex morphology.
Using the available data from Gaia DR3, we extracted a region on the sky that
contains Jhelum. We then applied the novel Locally Aligned Ant Technique (LAAT)
on the position and proper motion space of stars belonging to the selected
region to highlight the stars that are closely aligned with a local manifold in
the data and the stars belonging to regions of high local density. We find that
the overdensity representing the stream in proper motion space is composed of
two components, and show the correspondence of these two signals to the
previously reported narrow and broad spatial components of Jhelum. We made use
of the radial velocity measurements provided by the $S^5$ survey to confirm,
for the first time, a separation between the two components in radial velocity.
We show that the narrow and broad components have velocity dispersions of
$4.84^{+1.23}_{-0.79}$~km/s and $19.49^{+2.19}_{-1.84}$~km/s, and metallicity
dispersions of $0.15^{+0.18}_{-0.10}$ and $0.34^{+0.13}_{-0.09}$, respectively.
These measurements, and the difference in component widths, could be explained
with a scenario where Jhelum is the remnant of a GC embedded within a DG that
were accreted onto the Milky Way during their infall. Although the properties
of Jhelum can be explained with this merger scenario, other progenitors of the
narrow component remain possible such as a nuclear star cluster or a DG. To
rule these possibilities out, we would need more observational data of member
stars of the stream. Our analysis highlights the importance of the internal
structure of streams with regards to their formation history.
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