HST Proper Motion of Andromeda III. Another Satellite Coorbiting the M31 Satellite Plane

• Published in: The Astrophysical journal Vol. 975; no. 1; pp. 138 - 147
• Main Authors: Casetti-Dinescu, Dana I., Pawlowski, Marcel S., Girard, Terrence M., Kanehisa, Kosuke Jamie, Petroski, Alexander, Martone, Max, Kozhurina-Platais, Vera, Platais, Imants
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.11.2024; IOP Publishing
• Subjects: Aerial surveys; Andromeda Galaxy; Cameras; Galaxies; Local Group; Proper motion; Satellites; Space astrometry; Stellar motions
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ad7b10

Abstract We measure the absolute proper motion of Andromeda III (And III) using Advanced Camera for Surveys/Wide Field Channel and WFPC2 exposures spanning an unprecedented 22 yr time baseline. The WFPC2 exposures have been processed using a deep-learning centering procedure recently developed as well as an improved astrometric calibration of the camera. The absolute proper motion zero point is given by 98 galaxies and 16 Gaia EDR3 stars. The resulting proper motion is ( μ α , μ δ ) = (−10.5 ± 12.5, 47.5 ± 12.5) μ as yr −1 . We perform an orbit analysis of And III using two estimates of M31's mass and proper motion. We find that And III’s orbit is consistent with dynamical membership to the Great Plane of Andromeda system of satellites although with some looser alignment compared to the previous two satellites NGC 147 and NGC 185. And III is bound to M31 if M31's mass is M vir ≥ 1.5 × 10 12 M ⊙ .