CO emission in NGC 4438 : a case for tidal stripping ?

We present a ^12^CO(J=1-0) map of the peculiar spiral galaxy NGC 4438 in the Virgo cluster core. In addition to a strong central component associated with the optical disk, we detect some molecular emission coming from the NW side of the galaxy. This NW feature is shifted by 1' from the galaxian plane in the same direction as the neutral-gas, radio-continuum and X-ray emissions. We find a total H_2_ mass of about 4.1 10^9^ M_sun_. Because of its very peculiar shape, NGC 4438 has often been considered as the best candidate galaxy in the Virgo cluster for gas stripping by the hot intracluster medium. However, the molecular is too dense to be easily swept, and the stellar tails only can be of tidal origin. We propose that a collision with the nearby companion NGC 4435 is at the origin of the observed distortions of NGC 4438. The efficiency of the tidal forces is proved by numerical simulations of the encounter with a simple test-particle code using a hyperbolic retrograde orbit. This suggests that the tidal gas-stripping mechanism in galaxy clusters could be more efficient than was previously thought.