Proper Motion of the Sextans Dwarf Galaxy from Subaru Suprime-Cam Data

TL;DR

This study measures the proper motion of the Sextans dwarf galaxy using Subaru data over 10 years, revealing its orbit and motion characteristics relative to the Milky Way.

Contribution

First precise proper motion measurement of Sextans using Subaru Suprime-Cam data calibrated with Gaia DR1, providing insights into its orbit and galactic dynamics.

Findings

Proper motion of Sextans: (-0.409, -0.047) mas/yr.

Orbit is low eccentricity with a 3 Gyr period.

Sextans is near apocenter, not part of the polar satellite structure.

Abstract

We have measured the absolute proper motion of the Sextans dwarf spheroidal galaxy using Subaru Suprime-Cam images taken at three epochs, with a time baseline of ~ 10 years. We astrometrically calibrate each epoch by constructing distortion-correction maps from the best available Subaru Suprime-Cam dithered data sets and from Gaia DR1 positions. The magnitude limit of the proper-motion study is V ~ 24. The area covered is 26.7 x 23.3 arcmin, which is still within the core radius of Sextans. The derived proper motion is (mu_a, mu_d) = (-0.409 +/- 0.050, -0.047 +/- 0.058) mas/yr. The direction of motion is perpendicular to the major axis of the galaxy. Our measurement, combined with radial velocity and distance from the literature, implies a low eccentricity orbit, with a moderate inclination to the Galactic plane, and a period of 3 Gyr. Sextans is now some 0.4 Gyr away from its pericenter ( r_peri ~ 75 kpc), moving toward its apocenter (r_apo ~ 132 kpc). Its orbit is inconsistent with membership to the vast polar structure of Galactic satellites.