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We present deep Magellan/Megacam stellar photometry of four recentlydiscovered faint Milky Way satellites: Sagittarius II (Sgr II), Reticulum II(Ret II), Phoenix II (Phe II), and Tucana III (Tuc III). Our photometry reaches~2-3 magnitudes deeper than the discovery data, allowing us to revisit theproperties of these new objects (e.g., distance, structural properties,luminosity measurements, and signs of tidal disturbance). The satellitecolor-magnitude diagrams show that they are all old (~13.5 Gyr) and metal-poor([Fe/H]$\lesssim-2.2$). Sgr II is particularly interesting as it sits in anintermediate position between the loci of dwarf galaxies and globular clustersin the size-luminosity plane. The ensemble of its structural parameters is moreconsistent with a globular cluster classification, indicating that Sgr II isthe most extended globular cluster in its luminosity range. The other threesatellites land directly on the locus defined by Milky Way ultra-faint dwarfgalaxies of similar luminosity. Ret II is the most elongated nearby dwarfgalaxy currently known for its luminosity range. Our structural parameters forPhe II and Tuc III suggest that they are both dwarf galaxies. Tuc III is knownto be associated with a stellar stream, which is clearly visible in ourmatched-filter stellar density map. The other satellites do not show any clearevidence of tidal stripping in the form of extensions or distortions. Finally,we also use archival HI data to place limits on the gas content of each object.

A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III