paper

Tidal Signatures in the Faintest Milky Way Satellites: The Detailed Properties of Leo V, Pisces II and Canes Venatici II

arXiv:1111.6608 · doi:10.1088/0004-637X/756/1/79

Abstract

We present deep wide-field photometry of three recently discovered faint Milky Way 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 ( 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] ), 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 ($\la 10$ Gyr) possibly sets them apart from the other satellites at Galactocentric distances $\ga 150$ kpc. We present a new compilation of structural data for all Milky Way 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 2- level. However, the faintest satellites tend to be more aligned toward the Galactic center, and those satellites with the highest ellipticity ($\ga 0.4$) have orientations () in the range . 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.

25 pages, 7 figures, ApJ accepted; version updated to match ApJ accepted

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