TIDAL SIGNATURES IN THE FAINTEST MILKY WAY SATELLITES: THE DETAILED PROPERTIES OF LEO V, PISCES II, AND CANES VENATICI II

We present deep wide-field photometry of three recently discovered faint Milky Way (MW) satellites: Leo V, Pisces II, and Canes Venatici II. Our main goals are to study the structure and star formation history of these dwarfs; we also search for signs of tidal disturbance. The three satellites have similar half-light radii (similar to 60-90 pc) but a wide range of ellipticities. Both Leo V and CVn II show hints of stream-like overdensities at large radii. An analysis of the satellite color-magnitude diagrams shows that all three objects are old (>10 Gyr) and metal-poor ([Fe/H] similar to-2), though neither the models nor the data have sufficient precision to assess when the satellites formed with respect to cosmic reionization. The lack of an observed younger stellar population (less than or similar to 10 Gyr) possibly sets them apart from the other satellites at Galactocentric distances greater than or similar to 150 kpc. We present a new compilation of structural data for all MW satellite galaxies and use it to compare the properties of classical dwarfs to the ultra-faints. The ellipticity distribution of the two groups is consistent at the similar to 2 sigma level. However, the faintest satellites tend to be more aligned toward the Galactic Center, and those satellites with the highest ellipticity (greater than or similar to 0.4) have orientations (Delta theta(GC)) in the range 20 degrees less than or similar to Delta theta(GC) less than or similar to 40 degrees. This latter observation is in rough agreement with predictions from simulations of dwarf galaxies that have lost a significant fraction of their dark matter halos and are being tidally stripped.