Star Formation in the Cometary Tails Associated with Cluster Galaxies

We investigate the star-formation in cometary tails of galaxies in clusters. In particular, we focus on the evolution of molecular clouds in the tails that generate the stars. Assuming that the gas tails had been derived from the galaxies through ram-pressure stripping, we found that the gas must have been stripped mostly not in the form of molecular clouds, but in the form of HI gas or molecular gas that is not in clouds. Moreover, the molecular clouds are condensed in the tails even away from the host galaxies. We also found that magnetic fields may be required to suppress Kelvin-Helmholtz (KH) instability on the surface of molecular clouds, because otherwise KH instability may destroy the molecular clouds before stars are formed in them.