M/L's in dSph's: Dark Matter or Tidal Disruption?

Details M/L's in dSph's: Dark Matter or Tidal Disruption? M/L's in dSph's: Dark Matter or Tidal Disruption?

Feb 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002noao.prop..353m&link_type=abstract

NOAO Proposal ID #2002A-0353

Physics

Scientific paper

Using a proven photometric technique for separating metal-poor giant stars from foreground dwarfs, we have mapped the distribution of associated giant stars to well past the nominal tidal radius (r_t) of seven Galactic dSph galaxies and globular clusters. In each case, while a King profile suitably fits the central density profiles, the profile departs from a King function at large r, revealing a ``break population" of stars outside the nominal r_t. The relative density at which the profile departs from a King function is correlated with the inferred M/L ratios of these objects. Two hypotheses for this correlation make different predictions for the run of velocity dispersion with radius, σ_v(r): (1) Higher M/L objects harbor more extended dark matter halos that support secondary, bound ``break'' populations. This model predicts declining σ_v's at large r. (2) Higher M/L ratios reflect higher degrees of virial non- equilibrium in the parent objects, thus invalidating a basic precept underlying the use of core σ_v's to obtain masses. Tidal disruption predicts rising σ_v's with r. Our survey identifies exactly the stars needed to undertake this key discriminatory test of dark matter. To wit, we propose to measure σ_v(r) trends in the Leo I and Leo II dSphs' to larger radii than have previously been explored. The fact that we have found evidence for tidal tails on each of these most distant satellites of the Milky Way has important implications for the tidal field and total mass of the Galaxy. We are also proposing to extend our photometric survey of these two dSph galaxies in order to cover a large area, probe deeper to improve our S/N, and more clearly delineate any extended or detached tidal tails.

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