We present the results of a wide-field ( V,I ) photometric study of the red-giant branch ( RGB ) stars in the outer halo of M31 , in a field located 30 to 35 kpc from the center of the galaxy along the southeast minor axis .
At this remote location , we find that RGB stars belonging to M31 are sparsely but definitely present , after statistical subtraction of field contamination .
We derive the metallicity distribution ( MDF ) for the halo stars using interpolation within a standard ( I,V - I ) grid of RGB evolutionary tracks .
The halo MDF is quite broad but dominated by a moderately high-metallicity population peaking at [ m/H ] \sim - 0.5 , strikingly different from the [ m/H ] \sim - 1.3 level which characterizes the outer halo of the Milky Way .
However , the shape and peak metallicity for this region are entirely similar to those found in other studies for the inner regions of the M31 halo , particularly our previous study of a 20-kpc region ( Durrell , Harris , & Pritchet 2001 ) employing similar data .
In summary , we find no evidence for a metallicity gradient or systematic change in the MDF out to quite large distances in the M31 halo : it appears to be a homogeneous and moderately metal-rich subsystem of the galaxy at all locations .
The star counts in the 30-kpc field are also consistent with the r ^ { 1 / 4 } law that fits the interior regions of the M31 spheroid surface brightness profile .
The metal-rich MDF and the r ^ { 1 / 4 } spheroid suggests M31 more strongly resembles a giant elliptical galaxy than other , Milky-Way-like , spirals .