Study of structural parameters and systemic proper motion of Sextans dwarf spheroidal galaxy with Subaru Hyper Suprime-Cam data

Abstract

ABSTRACT 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, the HSC data enable a secure selection of member star candidates based on the colour–magnitude cut, yielding about 10 000 member candidates at magnitudes down to i ∼ 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 ϵ ≃ 0.25 and the core and tidal radii of Rc = (368.4 ± 8.5) pc and Rt = (2.54 ± 0.046) kpc, respectively. Then using the two HSC data sets of 2.66 yr time baseline on average, we find the systemic proper motions of Sextans to be (μα, μδ) = (−0.448 ± 0.075, 0.058 ± 0.078) mas yr−1, which are 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 ground-based, large-aperture telescope data that cover a wide solid angle of the sky and have a long time baseline, such as the upcoming data from Legacy Survey of Space and Time (LSST), can be used to study systemic proper motions of dwarf galaxies.