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We exploit data from the Pan-Andromeda Archaeological Survey (PAndAS) tostudy the extended structures of M31's dwarf elliptical companions, NGC147 andNGC185. Our wide-field, homogeneous photometry allows to construct deepcolour-magnitude diagrams (CMDs) which reach down to $\sim3$ mag below the redgiant branch (RGB) tip. We trace the stellar components of the galaxies tosurface brightness of $\mu_g \sim 32$ mag arcsec$^{-2}$ and show they have muchlarger extents ($\sim5$ kpc radii) than previously recognised. While NGC185retains a regular shape in its peripheral regions, NGC147 exhibits pronouncedisophotal twisting due to the emergence of symmetric tidal tails. We fit singleSersic models to composite surface brightness profiles constructed from diffuselight and star counts and find that NGC147 has an effective radius almost 3times that of NGC185. In both cases, the effective radii that we calculate arelarger by a factor of $\sim2$ compared to most literature values. We alsocalculate revised total magnitudes of $M_g=-15.36\pm0.04$ for NGC185 and$M_g=-16.36\pm0.04$ for NGC147. Using photometric metallicities computed forRGB stars, we find NGC185 to exhibit a metallicity gradient of[Fe/H]$\sim-0.15$ dex/kpc over the radial range 0.125 to 0.5 deg. On the otherhand, NGC147 exhibits almost no metallicity gradient, $\sim-0.02$ dex/kpc from0.2 to 0.6 deg. The differences in the structure and stellar populations in theoutskirts of these systems suggest that tidal influences have played animportant role in governing the evolution of NGC147.

A PAndAS view of M31 dwarf elliptical satellites: NGC147 and NGC185