2017MNRAS.468.2850J

We present the discovery of rotation in quenched, low-mass early-type galaxies that are isolated. This finding challenges the claim that (all) rotating dwarf early-type galaxies in clusters were once spiral galaxies that have since been harassed and transformed into early-type galaxies. Our search of the Sloan Digital Sky Survey data within the Local Volume (z < 0.02) has yielded a sample of 46 galaxies with a stellar mass M_* <= 5 x 10⁹ M_☉ (median M_* ∼ 9.29 x 10⁸ M_☉), a low Hα equivalent width EW_Hα < 2 Å, and no massive neighbour (M_* >= 3 x 10¹⁰ M_☉) within a velocity interval of ΔV = 500 km s^–1 and a projected distance of ∼1 Mpc. Nine of these galaxies were subsequently observed with Keck Echellette Spectrograph and Imager and their radial kinematics are presented here. These extend out to the half-light radius R_e in the best cases, and beyond R_e/2 for all. They reveal a variety of behaviours similar to those of a comparison sample of early-type dwarf galaxies in the Virgo cluster observed by Toloba et al. Both samples have similar frequencies of slow and fast rotators, as well as kinematically decoupled cores. This, and especially the finding of rotating quenched low-mass galaxies in isolation, reveals that the early-type dwarfs in galaxy clusters need not be harassed or tidally stirred spiral galaxies.