We present a new , probabilistic method for determining the systemic proper motions of Milky Way ( MW ) ultra-faint satellites in the Dark Energy Survey ( DES ) .
We utilize the superb photometry from the first public data release ( DR1 ) of DES to select candidate members , and cross-match them with the proper motions from Gaia DR2 .
We model the candidate members with a mixture model ( satellite and MW ) in spatial and proper motion space .
This method does not require prior knowledge of satellite membership , and can successfully determine the tangential motion of thirteen DES satellites .
With our method we present measurements of the following satellites : Columba I , Eridanus III , Grus II , Phoenix II , Pictor I , Reticulum III , and Tucana IV ; this is the first systemic proper motion measurement for several and the majority lack extensive spectroscopic follow-up studies .
We compare these to the predictions of Large Magellanic Cloud satellites and to the vast polar structure .
With the high precision DES photometry we conclude that most of the newly identified member stars are very metal-poor ( [ Fe/H ] \lesssim - 2 ) similar to other ultra-faint dwarf galaxies , while Reticulum III is likely more metal-rich .
We also find potential members in the following satellites that might indicate their overall proper motion : Cetus II , Kim 2 , and Horologium II ; however , due to the small number of members in each satellite , spectroscopic follow-up observations are necessary to determine the systemic proper motion in these satellites .