We present a large area photometric survey of the Ursa Minor dwarf spheroidal galaxy and its environs. This survey is intended to trace the distribution of stars outside the nominal tidal radius of this system. Observations were made with the Washington M , Washington T 2 , and DDO51 filters, which in combination have been shown previously to provide reliable stellar luminosity classification for K type stars. We identify giant star candidates with the same distance and metallicity as known Ursa Minor RGB stars extending to approximately 3 • from the center of the dSph. Comparison to catalogues of stars within the tidal radius of Ursa Minor that have been observed spectroscopically suggests that our photometric luminosity classification is 100% accurate. Over a large fraction of the survey area, our photometry is deep enough that blue horizontal branch stars associated with Ursa Minor can also be identified. The spatial distribution of both the candidate Ursa Minor giant stars and the candidate BHB stars are remarkably similar, and, for both samples, a large fraction of the stars are found outside the nominal tidal radius of Ursa Minor. An isodensity contour map of the surface density of stars within the tidal radius of Ursa Minor reveals several morphological peculiarities: (1) The highest density of dSph stars is not found at the center of symmetry of the outer isodensity contours, but instead is offset southwest of center. (2) The overall shape of the outer contours does not appear to be elliptical, but appears S-shaped. A surface density profile was derived for Ursa Minor and compared to those derived from previous studies. We find that previously determined King profiles with ∼ 50 ′ tidal radii do not fit well the distribution of candidate UMi stars identified in this study, which extends to greater radii than these other surveys. A King profile with a much larger tidal radius produces a reasonable fit, however a power law with index −3 provides an even better fit to the densities at radii greater than 20 ′ . The existence of Ursa Minor associated stars at large distances from the core of the galaxy, the peculiar morphology of the galaxy within its tidal radius, and the shape of its surface density profile all suggest that this system is evolving significantly due to the tidal influence of the Milky Way. However, the photometric data on Ursa Minor stars alone do not allow us to determine if the candidate extratidal stars are now unbound or if they remain bound to the dSph within an extended dark matter halo.

We analyze velocity dispersion profiles for the Draco and Ursa Minor (UMi) dwarf spheroidal (dSph) galaxies based on published and new Keck HIRES spectra for stars in the outer UMi field. Washington+DDO51 filter photometric catalogs provide additional leverage on membership of individual stars, and beyond 0.5 King limiting radii (r lim ) identify bona fide dSph members up to 4.5 times more efficiently than simple color-magnitude diagram selections. Previously reported "cold populations" at r lim are not obvious in the data and appear only with particular binning; more or less constant and platykurtic dispersion profiles are characteristic of these dSphs to large radii. We report discovery of UMi stars to at least 2.7r lim (i.e., 210 ′ or 4 kpc). Even with conservative assumptions, a UMi mass of M > 4.9 × 10 8 M ⊙ is required to bind these stars, implying an unlikely global mass-to-light ratio of M/L > 900 (M/L) ⊙ . We conclude that we have found stars tidally stripped from UMi.

In numerous studies of the outer Galactic halo some evidence for accretion has been found. If the outer halo did form in part or wholly through merger events, we might expect to find coherent streams of stars and globular clusters following similar orbits as their parent objects, which are assumed to be present or former Milky Way dwarf satellite galaxies. We present a study of this phenomenon by assessing the likelihood of potential descendant ``dynamical families'' in the outer halo. We conduct two analyses: one that involves a statistical analysis of the spatial distribution of all known Galactic dwarf satellite galaxies (DSGs) and globular clusters, and a second, more specific analysis of those globular clusters and DSGs for which full phase space dynamical data exist. In both cases our methodology is appropriate only to members of descendant dynamical families that retain nearly aligned orbital poles today. Since the Sagittarius dwarf (Sgr) is considered a paradigm for the type of merger/tidal interaction event for which we are searching, we also undertake a case study of the Sgr system and identify several globular clusters that may be members of its extended dynamical family. (ABRIDGED)Comment: accepted by ApJ, 57 pages, 13 figures, AASTeX forma