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We present kinematic and metallicity profiles for the M31 dwarf elliptical(dE) satellite galaxies NGC 147 and NGC 185. The profiles represent the mostextensive spectroscopic radial coverage for any dE galaxy, extending to aprojected distance of eight half-light radii (8 r_eff = 14'). We achieve thiscoverage via Keck/DEIMOS multislit spectroscopic observations of 520 and 442member red giant branch stars in NGC 147 and NGC 185, respectively. In contrastto previous studies, we find that both dEs have significant internal rotation.We measure a maximum rotational velocity of 17+/-2 km/s for NGC 147 and 15+/-5km/s for NGC 185. The velocity dispersions decrease gently with radius with anaverage dispersion of 16+/-1 km/s for NGC 147 and 24+/-1 km/s for NGC 185. BothdEs have internal metallicity dispersions of 0.5 dex, but show no evidence fora radial metallicity gradient. We construct two-integral axisymmetric dynamicalmodels and find that the observed kinematical profiles cannot be explainedwithout modest amounts of non-baryonic dark matter. We measure centralmass-to-light ratios of ML_V = 4.2+/-0.6 and ML_V = 4.6+/-0.6 for NGC 147 andNGC 185, respectively. Both dE galaxies are consistent with being primarilyflattened by their rotational motions, although some anisotropic velocitydispersion is needed to fully explain their observed shapes. The velocityprofiles of all three Local Group dEs (NGC 147, NGC 185 and NGC 205) suggestthat rotation is more prevalent in the dE galaxy class than previously assumed,but is often manifest only at several times the effective radius. Since all dEsoutside the Local Group have been probed to only inside the effective radius,this opens the door for formation mechanisms in which dEs are transformed orstripped versions of gas-rich rotating progenitor galaxies.

Local Group Dwarf Elliptical Galaxies: II. Stellar Kinematics to Large Radii in NGC 147 and NGC 185