Counter-rotating molecular gas in NGC 4546

The detection of 9.6 +/- 2.9 x 107 solar mass of molecular gas in the barred S0 galaxy NGC 4546 is reported. This galaxy has an 8 kpc wide disk of ionized gas rotating opposite to the stellar disk (but with approximately the same velocity magnitude). The detected molecular gas has the same motion as the ionized gas (and the atomic gas), counter-rotating with respect to the stars. The molecular gas is concentrated more on the western side of the galaxy, while the atomic gas is apparently more prevalent on the eastern side. The peculiar gas kinematics of NGC 4546 likely come from a past acquisition of gas, probably through a collision with a dwarf galaxy whose relative velocity was retrograde with respect to the galaxy spin. However, the lack of evidence for starburst activity, and the length of time required to form a stable disk structure from an accreted companion, suggest that there is little interaction between the pre-existing and accreted gas at this time