Substructure in the stellar halo near the Sun. II. Characterisation of independent structures. (arXiv:2201.02405v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Ruiz_Lara_T/0/1/0/all/0/1">Tomás Ruiz-Lara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matsuno_T/0/1/0/all/0/1">Tadafumi Matsuno</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lovdal_S/0/1/0/all/0/1">S. Sofie Lövdal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Helmi_A/0/1/0/all/0/1">Amina Helmi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dodd_E/0/1/0/all/0/1">Emma Dodd</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koppelman_H/0/1/0/all/0/1">Helmer H. Koppelman</a>
Context: In an accompanying paper by L”ovdal et al, we presented a
data-driven method for clustering in Integrals of Motion space and applied it
to a large sample of nearby halo stars with 6D phase-space information. Aims:
Our goal is to establish the reality of the clusters and groups through a
combined study of their stellar populations to gain insights into the accretion
history of the Milky Way. Methods: We develop a procedure that quantifies the
similarity of clusters based on the Kolmogorov-Smirnov test using their
metallicity distribution functions, and an isochrone fitting method to
determine their average age, which is also used to compare the distribution of
stars in the Colour-Absolute magnitude diagram. Considering their distributions
in Integrals of Motion space as well, this allows us to group clusters into
substructures, and to compare substructures with one another. Results: We find
that the 67 clusters identified by our algorithm can be merged into 12 extended
substructures, while eight small clusters remain as such. The large
substructures include the previously known Gaia-Enceladus, Helmi streams,
Sequoia, and Thamnos 1 and 2. We identify a few overdensities that can be
associated with the hot thick disc and which host a small metal-poor
population. Especially notable is the largest substructure in our sample which,
although peaking at the metallicity characteristic of the thick disk has a very
well populated metal-poor component, and dynamics intermediate between the hot
thick disc and the halo. We also identify additional debris in the region
occupied by Sequoia with clearly distinct kinematics. Although only a small
subset of the stars in our sample have chemical abundance information, we are
able to identify different trends of [Mg/Fe] vs [Fe/H] for the various
substructures confirming our dissection of the nearby halo. Conclusions: We
find… [abridged version]
Context: In an accompanying paper by L”ovdal et al, we presented a
data-driven method for clustering in Integrals of Motion space and applied it
to a large sample of nearby halo stars with 6D phase-space information. Aims:
Our goal is to establish the reality of the clusters and groups through a
combined study of their stellar populations to gain insights into the accretion
history of the Milky Way. Methods: We develop a procedure that quantifies the
similarity of clusters based on the Kolmogorov-Smirnov test using their
metallicity distribution functions, and an isochrone fitting method to
determine their average age, which is also used to compare the distribution of
stars in the Colour-Absolute magnitude diagram. Considering their distributions
in Integrals of Motion space as well, this allows us to group clusters into
substructures, and to compare substructures with one another. Results: We find
that the 67 clusters identified by our algorithm can be merged into 12 extended
substructures, while eight small clusters remain as such. The large
substructures include the previously known Gaia-Enceladus, Helmi streams,
Sequoia, and Thamnos 1 and 2. We identify a few overdensities that can be
associated with the hot thick disc and which host a small metal-poor
population. Especially notable is the largest substructure in our sample which,
although peaking at the metallicity characteristic of the thick disk has a very
well populated metal-poor component, and dynamics intermediate between the hot
thick disc and the halo. We also identify additional debris in the region
occupied by Sequoia with clearly distinct kinematics. Although only a small
subset of the stars in our sample have chemical abundance information, we are
able to identify different trends of [Mg/Fe] vs [Fe/H] for the various
substructures confirming our dissection of the nearby halo. Conclusions: We
find… [abridged version]
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