On the nature of ultra-faint dwarf galaxy candidates I: DES1, Eridanus
  III and Tucana V
  We use deep Gemini/GMOS-S $g,r$ photometry to study the three ultra-faint
dwarf galaxy candidates DES1, Eridanus III (Eri III) and Tucana V (Tuc V).
Their total luminosities, $M_V$(DES1) $ = -1.42\pm0.50$ and $M_V$(Eri III) $ =
-2.07\pm0.50$, and mean metallicities, [Fe/H] $=-2.38^{+0.21}_{-0.19}$ and
[Fe/H] $=-2.40^{+0.19}_{-0.12}$, are consistent with them being ultra-faint
dwarf galaxies as they fall just outside the 1-sigma confidence band of the
luminosity-metallicity relation for Milky Way satellite galaxies. However,
their positions in the size-luminosity relation suggests that they are star
clusters. Interestingly, DES1 and Eri III are at relatively large
Galactocentric distances with DES1 located at $D_{GC} = 74\pm$4 kpc and Eri III
at $D_{GC} = 91\pm$4 kpc. In projection both objects are in the tail of gaseous
filaments trailing the Magellanic Clouds and have similar 3D-separations from
the Small Magellanic Cloud (SMC): $\Delta D_{SMC,DES1}$ = 31.7 kpc and $\Delta
D_{SMC,Eri III}$ = 41.0 kpc, respectively. It is plausible that these stellar
systems are metal-poor SMC satellites. Tuc V represents an interesting
phenomenon in its own right. Our deep photometry at the nominal position of Tuc
V reveals a low-level excess of stars at various locations across the GMOS
field without a well-defined centre. A SMC Northern Overdensity-like isochrone
would be an adequate match to the Tuc V colour-magnitude diagram, and the
proximity to the SMC ($12.1^\circ$; $\Delta D_{SMC,Tuc V}=13$ kpc) suggests
that Tuc V is either a chance grouping of stars related to the SMC halo or a
star cluster in an advanced stage of dissolution.
