From spirals to lenticulars: Evidence from the rotation curves and mass models of three early-type galaxies

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). In this work, we derive rotation curves for three lenticular galaxies from the ATLAS(3D) 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 mu m 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 a 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; and (4) one galaxy (NGC 3626) is poorly fit 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 they 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.