A Subaru/suprime-cam Survey of M31’s Spheroid along the South-east Minor Axis

We have used Suprime-Cam on the Subaru Telescope to conduct a V and I-band imaging survey of fields sampling the spheroid of the Andromeda galaxy along its south-east minor axis. Our photometric data are deep enough to resolve stars down to the red clump. Based on a large and reliable sample of red giant stars available from this deep wide-field imager, we have derived metallicity distributions vs. radius and a surface brightness profile over projected distances of R = 23–66 kpc from the galaxy’s center. The metallicity distributions across this region shows a clear high mean metallicity and a broad distribution ([Fe/H]∼ −0.6 ± 0.5), and indicates no metallicity gradient within our observed range. The surface brightness profile at R > 40 kpc is found to be flatter than previously thought. It is conceivable that this part of the halo samples as yet unidentified, metal-rich substructure. Subject headings: galaxies: individual (M31) — galaxies: halos — galaxies: structure