Turning the Tides on the Ultra-Faint Dwarf Spheroidal Galaxies: Coma
  Berenices and Ursa Major II
  We present deep CFHT/MegaCam photometry of the ultra-faint Milky Way
satellite galaxies Coma Berenices (ComBer) and Ursa Major II (UMa II). These
data extend to r~25, corresponding to three magnitudes below the main sequence
turn-offs in these galaxies. We robustly calculate a total luminosity of
M_V=-3.8 +/- 0.6 for ComBer and M_V=-3.9 +/- 0.5 for UMa II, in agreement with
previous results. ComBer shows a fairly regular morphology with no signs of
active tidal stripping down to a surface brightness limit of 32.4 magarcsec^-2.
Using a maximum likelihood analysis, we calculate the half-light radius of
ComBer to be r_half=74 +/- 4 pc (5.8 +/- 0.3 arcmin) and its ellipticity e=0.36
+/- 0.04. In contrast, UMa II shows signs of on-going disruption. We map its
morphology down to mu_V=32.6 mag arcsec^-2 and found that UMa II is larger than
previously determined, extending at least ~700 pc (1.2 deg on the sky) and it
is also quite elongated with an ellipticity of e=0.50 +/- 0.2. However, our
estimate for the half-light radius, 123 +/- 3 pc (14.1 +/- 0.3 arcmin) is
similar to previous results. We discuss the implications of these findings in
the context of potential indirect dark matter detections and galaxy formation.
We conclude that while ComBer appears to be a stable dwarf galaxy, UMa II shows
signs of on-going tidal interaction.
