We present kinematic and metallicity profiles for the M 31 dwarf elliptical ( dE ) satellite galaxies NGC 147 and NGC 185 .
The profiles represent the most extensive spectroscopic radial coverage for any dE galaxy , extending to a projected distance of eight half-light radii ( 8 r _ { eff } \sim 14 ^ { \prime } ) .
We achieve this coverage via Keck/DEIMOS multislit spectroscopic observations of 520 and 442 member red giant branch stars in NGC 147 and NGC 185 , respectively .
In contrast to previous studies , we find that both dEs have significant internal rotation .
We measure a maximum rotational velocity of 17 \pm 2 km s ^ { -1 } for NGC 147 and 15 \pm 5 km s ^ { -1 } for NGC 185 .
While both rotation profiles suggest a flattening in the outer regions , there is no indication that we have reached the radius of maximum rotation velocity .
The velocity dispersions decrease gently with radius with an average dispersion of 16 \pm 1 km s ^ { -1 } for NGC 147 and 24 \pm 1 km s ^ { -1 } for NGC 185 .
The average metallicity for NGC 147 is [ Fe/H ] = -1.1 \pm 0.1 and for NGC 185 is [ Fe/H ] = -1.3 \pm 0.1 ; both dEs have internal metallicity dispersions of 0.5 dex , but show no evidence for a radial metallicity gradient .
We construct two-integral axisymmetric dynamical models and find that the observed kinematical profiles can not be explained without modest amounts of non-baryonic dark matter .
We measure central mass-to-light ratios of M / L _ { V } = 4.2 \pm 0.6 and M / L _ { V } = 4.6 \pm 0.6 for NGC 147 and NGC 185 , respectively .
Both dE galaxies are consistent with being primarily flattened by their rotational motions , although some anisotropic velocity dispersion is needed to fully explain their observed shapes .
The velocity profiles of all three Local Group dEs ( NGC 147 , NGC 185 and NGC 205 ) suggest that 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 dEs outside the Local Group have been probed to only inside the effective radius , this opens the door for formation mechanisms in which dEs are transformed or stripped versions of gas-rich rotating progenitor galaxies .