Cospatial counterrotating stellar disks in the Virgo E7/S0 galaxy NGC 4550

Rubin, V.C., Graham, J.A., & Kenney, J.D.P. 1992, Ap. J. 394, L9.

Two cospatial stellar disks, one orbiting prograde, one orbiting retrograde, in NGC 4550, an E7/S0 galaxy in the core of the Virgo Cluster have been discovered. One of the stellar disks is coincident with a gas disk. Absorption and emission-line velocities for the two counterrotating components have been measured over about one-third of the optical diameter. It is proposed that after the initial stellar disk of NGC 4550 was formed, a substantial amount of counterrotating gas was acquired greater than or equal to 10 exp 9 yr ago. It then settled to the plane via dissipation; the bulk of the counterrotating stars most likely formed after the gas settled to the plane.