Counter-rotating gas disk in the S0 galaxy IC 560

Acounter-rotating gas disk has been detected in the SA0 galaxy IC 560 located at the periphery of a sparse group of six late-type galaxies. The pattern of gas excitation and mid-infrared colors are indicative of ongoing star formation within 1 kpc of the center. Outside the gas disk with star formation the large-scale stellar disk of the galaxy has an old age and a very low metallicity, [Z/H] ≈ −1. The source of external gas accretion onto IC 560 is undetected; the only option is a single infall of a companion rich in high-metallicity gas.