What can Gaia (with TMT) say about Sculptor's Core?
  Walker et al.'s Magellan/MMFS Survey survey identified 1355 red giant
candidates in the dwarf spheroidal galaxy Sculptor. We find that the Gaia
satellite will be able to measure the proper motions of 139 of these with a
precision of between 13 and 20 km/s. Using a Jeans analysis and 5-parameter
density model we show that this allows a determination of the mass within the
deprojected half-light radius to within 16% and a measurement of the dark
matter density exponent gamma to within 0.68 within that radius. If, even at
first light, the TMT observes Sculptor then the combined observations will
improve the precision on these proper motions to about 5 km/s, about 5 years
earlier than would be possible without Gaia, further improving the precision of
gamma to 0.27. Using a bimodal stellar population model for Sculptor the
precision of gamma improves by about 30%. This suggests that Gaia (with TMT) is
capable of excluding a cored profile of the kind predicted by CDM simulations
with 2 sigma (4 sigma) of confidence.
