Abstract / Description of output
We present and analyze the positions, distances, and radial velocities
for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's
halo, drawn from SDSS DR8. We search for position-velocity substructure
in these data, a signature of the hierarchical assembly of the stellar
halo. Using a cumulative "close pair distribution" as a statistic in the
four-dimensional space of sky position, distance, and velocity, we
quantify the presence of position-velocity substructure at high
statistical significance among the BHB stars: pairs of BHB stars that
are close in position on the sky tend to have more similar distances and
radial velocities compared to a random sampling of these overall
distributions. We make analogous mock observations of 11 numerical halo
formation simulations, in which the stellar halo is entirely composed of
disrupted satellite debris, and find a level of substructure comparable
to that seen in the actually observed BHB star sample. This result
quantitatively confirms the hierarchical build-up of the stellar halo
through a signature in phase (position-velocity) space. In detail, the
structure present in the BHB stars is somewhat less prominent than that
seen in most simulated halos, quite possibly because BHB stars represent
an older sub-population. BHB stars located beyond 20 kpc from the
Galactic center exhibit stronger substructure than at r gc < 20 kpc.
Original language | English |
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Journal | Astrophysical Journal |
DOIs | |
Publication status | Published - 12 Aug 2011 |
Keywords / Materials (for Non-textual outputs)
- astro-ph.GA