New Proper Motions of the Small Magellanic Cloud Using HST and Implications for Milky Way Mass

Abstract

AbstractAs new work on the proper motions (PMs) of the Large Magellanic Cloud (LMC) has come out, our view of the history of the Magellanic Clouds has evolved. We now believe they are on their first infall into the Milky Way (MW), having been tidally bound at the start of infall (though not necessarily now). Combining these observations with initial PMs of the Small Magellanic Cloud (SMC) suggests a new formation mechanism of the Magellanic Stream through the stripping of material from the SMC. However, large uncertainties remain in the exact mass of the LMC. We present a measurement of the systemic proper motions of the SMC from astrometry with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST), covering a ~3 year baseline of 30 fields with background QSOs. We find these motions to be μW = −0.82 ± 0.06 mas/yr and μN = −1.23 ± 0.07 mas/yr. Combining these measurements with previous efforts in studying the Clouds will help constrain their interactions with each other and the MW, including the mass of the LMC and the MW, as well as provide new insight into the internal dynamics of the SMC.