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?

Aug 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001noao.prop..382m&link_type=abstract

NOAO Proposal ID #2001B-0382

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 with 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, and potentially obviating the need for dark matter in these systems. Tidal disruption predicts rising σ_v's with r. Our survey identifies exactly the stars - the rare, bright, associated giant stars in the overwhelming sea of foreground Galactic stars - needed to undertake this key discriminatory test of dark matter. To wit, we propose to measure σ_v(r) trends in the Carina and Sculptor dSphs to larger r than have previously been explored for any dSph.

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