ACS Photometry of Newly Discovered Globular Clusters in the Outer Halo of M31

We report the first results from deep ACS imaging of ten classical globularclusters in the far outer regions (15 < R_p < 100 kpc) of M31. Eight of theclusters, including two of the most remote M31 globular clusters presentlyknown, are described for the first time. Our F606W, F814W colour-magnitudediagrams extend ~ 3 magnitudes below the horizontal branch and clearlydemonstrate that the majority of these objects are old (> 10 Gyr), metal-poorclusters. Five have [Fe/H] ~ -2.1, while an additional four have -1.9 < [Fe/H]< -1.5. The remaining object is more metal-rich, with [Fe/H] ~ -0.70. Severalclusters exhibit the second parameter effect. Using aperture photometry, weestimate integrated luminosities and structural parameters for all clusters.Many, including all four clusters with projected radii greater than 45 kpc, arecompact and very luminous, with -8.9 < M_V < -8.3. These four outermostclusters are thus quite unlike their Milky Way counterparts, which aretypically diffuse, sub-luminous (-6.0 < M_V < -4.7) and more metal-rich (-1.8 <[Fe/H] < -1.3).