  Rotation curves have traditionally been difficult to trace for early-type
galaxies (ETGs) because they often lack a high-density disk of cold gas as in
late-type galaxies (LTGs). We derive rotation curves for three lenticular
galaxies from the ATLAS3D survey, combining CO data in the inner parts with
deep HI data in the outer regions, extending out to 10-20 effective radii. We
also use Spitzer photometry at 3.6 um to decompose the rotation curves into the
contributions of baryons and dark matter (DM). We find that (1) the
rotation-curve shapes of these ETGs are similar to those of LTGs of similar
mass and surface brightness; (2) the dynamically$-$inferred stellar
mass-to-light ratios are small for quiescent ETGs but similar to those of
star-forming LTGs; (3) the DM halos follow the same scaling relations with
galaxy luminosity as those of LTGs; (4) one galaxy (NGC 3626) is poorly fitted
by cuspy DM profiles, suggesting that DM cores may exist in high-mass galaxies
too. Our results indicate that these lenticular galaxies have recently
transitioned from LTGs to ETGs without altering their DM halo structure (e.g.,
via a major merger) and could be faded spirals. We also confirm that ETGs
follow the same radial acceleration relation as LTGs, reinforcing the notion
that this is a universal law for all galaxy types.
