Photometric metallicity ([Fe/H]_phot) distribution functions (MDFs) for all stars in the NE shelf fields (including MW contaminants; black solid open histogram), stars classified as M31 members (gray dashed open histogram; Section 3.1), and stars that probably belong to the NE shelf (p _sub > 0.5; Section 3.2.2). We assumed 12 Gyr PARSEC isochrones (Marigo et al. 2017) to determine [Fe/H]_phot (Section 2.2). The median [Fe/H]_phot for each sample is shown as arrows, where [Fe/H]_{phot ,med} = −0.41 is robust with respect to sample selection, indicating that the NE shelf is the dominant feature in the data (Section 3.3).