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

¹ ESO, Karl-Schwarschild-Strasse 2, 85748 Garching bei München, Germany
e-mail: ashelest@g.harvard.edu
² Department of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138, USA
³ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK

Received: 16 April 2020
Accepted: 16 June 2020

Abstract

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 μm 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.