Counter-rotating gaseous disks in the "Evil Eye" galaxy NGC4826

Abstract

SEVERAL elliptical and spheroidal galaxies have been shown, in recent years, to possess kinematically distinct subsystems. These may be in the form of a central stellar component whose rotation is not aligned with the rest of the galaxy^1,2, or of a gaseous disk, often at large radius, which is kinematically distinct from the main stellar component^3,4. A more unusual case is that of a counter-rotating gaseous component (with some associated stellar absorption) in the inner region of the flattened elliptical NGC4550⁵. All these cases are presumed to be signatures of violently interacting systems, which are the result of galaxy mergers or captures, as in NGC7252^6,7. Here we report the discovery of two counter-rotating gaseous disks in the otherwise normal early-type spiral (Sab(s)II; ref. 8) NGC4826. This is the most disk-like galaxy in which any kinematic substructure has yet been found, and our discovery raises the possibility, already suggested by Schweizer⁷, that even spiral galaxies may have undergone a significant degree of structural evolution due to mergers.