Kavli Affiliate: Naoki Yasuda
| First 5 Authors: Tian Qiu, Wenting Wang, Masahiro Takada, Naoki Yasuda, Željko Ivezić
| Summary:
We present proper motion measurements for more than $0.55$ million
main-sequence stars, by comparing astrometric positions of matched stars
between the multi-band imaging datasets from the Hyper Suprime-Cam (HSC) Survey
and the SDSS Stripe 82. In doing this we use $3$ million galaxies to
recalibrate the astrometry and set up a common reference frame between the two
catalogues. The exquisite depth and the nearly $12$ years of time baseline
between HSC and SDSS enable high-precision measurements of statistical proper
motions for stars down to $isimeq 24$. A validation of our method is
demonstrated by the agreement with the $Gaia$ proper motions, to the precision
better than $0.1$ mas yr$^{-1}$. To retain the precision, we make a correction
of the subtle effects due to the differential chromatic refraction in the SDSS
images based on the comparison with the $Gaia$ proper motions against colour of
stars, which is validated using the SDSS spectroscopic quasars. Combining with
the photometric distance estimates for individual stars based on the precise
HSC photometry, we show a significant detection of the net proper motions for
stars in each bin of distance out to $100$ kpc. The two-component tangential
velocities after subtracting the apparent motions due to our own motion display
rich phase-space structures including a clear signature of the Sagittarius
stream in the halo region of distance range $[10, 35]$ kpc. We also measure
the tangential velocity dispersion in the distance range $5-20$ kpc and find
that the data are consistent with a constant isotropic dispersion of $80pm 10
{rm km/s}$. More distant stars appear to have random motions with respect to
the Galactic centre on average.
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