Wide-field kinematic signatures of assembly in observed and simulated early-type galaxies

Hie evolutionary history of galaxies is written in their internal stellar kinematics. Detailed examinations of the chemodynamic properties of early-type galaxies (ETGs, Es and S0s) have forced a paradigm shift in our understanding of these objects, which are no longer viewed as only passively evolving, and having ceased star formation and mass growth long ago. We present the first ever wide-field 2D kinematic maps of ordinary elliptical and lenticular galaxies that cover their entire radial range, from center to halo. The maps show a clear two-zone pattern for almost the entire observational sample, with rapid disky rotation in their centers transitioning to slow and aligned rotation in the outer parts. The observations are compared with galaxies found in simulations; idealized major-merger remnants or cosmological simulations that resolve individual galaxies. We find that the merger remnants generally have high rotation in the outer parts which is not observed. The cosmological simulation produces galaxies that tend to match very well with our observations. We infer that elliptical and lenticular galaxies assembled in two zones: an inner zone that farmed by gas accretion in an early violent disk phase, and an outer zone that formed later from gas-poor minor mergers. These processes as well as late accretion of cold gas and major mergers, might explain the full range in present-day galaxy morphology.