We present deep , wide-field Subaru Hyper Suprime-Cam photometry of two recently discovered satellites of the Milky Way ( MW ) : Columba I and Triangulum II .
The color magnitude diagrams of both objects point to exclusively old and metal-poor stellar populations .
We re-derive structural parameters and luminosities of these satellites , and find M _ { V,Col~ { } I } = -4.2 \pm 0.2 for Col I and M _ { V,Tri~ { } II } = -1.2 \pm 0.4 for Tri II , with corresponding half-light radii of r _ { h,Col~ { } I } = 117 \pm 17 pc and r _ { h,Tri~ { } II } = 21 \pm 4 pc .
The properties of both systems are consistent with observed scaling relations for MW dwarf galaxies .
Based on archival data , we derive upper limits on the neutral gas content of these dwarfs , and find that they lack H I , as do the majority of observed satellites within the MW virial radius .
Neither satellite shows evidence of tidal stripping in the form of extensions or distortions in matched-filter stellar density maps or surface density profiles .
However , the smaller Tri II system is relatively metal-rich for its luminosity ( compared to other MW satellites ) , possibly because it has been tidally stripped .
Through a suite of orbit simulations , we show that Tri II is approaching pericenter of its eccentric orbit , a stage at which tidal debris is unlikely to be seen .
In addition , we find that Tri II may be on its first infall into the MW , which helps explain its unique properties among MW dwarfs .
Further evidence that Tri II is likely an ultra-faint dwarf comes from its stellar mass function , which is similar to those of other MW dwarfs .