Abstract / Description of output
We combine Gaia data release 1 astrometry with Sloan Digital
Sky Survey (SDSS) images taken some ∼10–15 years earlier, to measure
proper motions of stars in the halo of our Galaxy. The SDSS–Gaia proper motions have typical statistical errors of 2 mas yr−1 down to r ∼ 20 mag,
and are robust to variations with magnitude and colour. Armed with this
exquisite set of halo proper motions, we identify RR Lyrae, blue
horizontal branch (BHB), and K giant stars in the halo, and measure
their net rotation with respect to the Galactic disc. We find evidence
for a gently rotating prograde signal (〈Vϕ〉 ∼ 5–25 km s−1)
in the halo stars, which shows little variation with Galactocentric
radius out to 50 kpc. The average rotation signal for the three
populations is 〈Vϕ〉 = 14 ± 2 ± 10 (syst.) km s−1.
There is also tentative evidence for a kinematic correlation with
metallicity, whereby the metal richer BHB and K giant stars have
slightly stronger prograde rotation than the metal poorer stars. Using
the Auriga simulation suite, we find that the old (T
>10 Gyr) stars in the simulated haloes exhibit mild prograde
rotation, with little dependence on radius or metallicity, in general
agreement with the observations. The weak halo rotation suggests that
the Milky Way has a minor in situ halo component, and has undergone a
relatively quiet accretion history.
Original language | English |
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Journal | Monthly Notices of the Royal Astronomical Society |
Early online date | 25 May 2017 |
DOIs | |
Publication status | Published - 1 Sept 2017 |
Keywords / Materials (for Non-textual outputs)
- astro-ph.GA