Kavli Affiliate: Naoki Yasuda
| First 5 Authors: Akira Tokiwa, Masahiro Takada, Tian Qiu, Naoki Yasuda, Yutaka Komiyama
| Summary:
We use the Subaru Hyper Suprime-Cam (HSC) data to study structural parameters
and systemic proper motion of the Sextans dwarf spheroidal galaxy at the
heliocentric distance of 86 kpc, which is one of the most important targets for
studies of dark matter nature and galaxy formation physics. Thanks to the
superb image quality and wide area coverage of the Sextans field, the HSC data
enables a secure selection of member star candidates based on the
colour-magnitude cut, yielding about 10,000 member candidates at magnitudes
down to $isim 24$. We use a likelihood analysis of the two-dimensional
distribution of stars to estimate the structural parameters of Sextans taking
into account the contamination of foreground halo stars in the Milky Way, and
find that the member star distribution is well-fitted by an elliptical King
profile with ellipticity $epsilon simeq 0.25$ and the core and tidal radii of
$R_c=(368.4pm 8.5)$ pc and $R_t=(2.54pm 0.046)$ kpc, respectively. Then using
the two HSC datasets of 2.66 years time baseline on average, we find the
systemic proper motions of Sextans to be $(mu_alpha,
mu_delta)=(-0.448pm{0.075},0.083pm{0.078})$ $mathrm{mas}
mathrm{yr}^{-1}$, which is consistent with some of the previous works using
the $Gaia$ data of relatively bright member stars in Sextans. Thus, our results
give a demonstration that a ground-based, large-aperture telescope data which
covers a wide solid angle of the sky and has a long time baseline, such as the
upcoming LSST data, can be used to study systemic proper motions of dwarf
galaxies.
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