The strong transformation of spiral galaxies infalling into massive clusters atz≈ 0.2

We describe two peculiar galaxies falling into the massive galaxy clusters Abell 1689 (z≈ 0.18) and Abell 2667 (z≈ 0.23), respectively. Hubble Space Telescope (HST) images show extraordinary trails composed of bright blue knots (−16.5 < M < −11.5 mag) and stellar streams associated with each of these systems. Combining optical, near- and mid-infrared and radio observations we prove that while both galaxies show similar extended trails of star-forming knots, their recent star formation histories are different. One (≈L*) is experiencing a strong burst of star formation, appearing as a rare example of a luminous infrared cluster galaxy. In comparison, the other (≈0.1L*) has recently ceased its star formation activity. Our model suggests that the morphologies and star formation in these galaxies have been influenced by the combined action of tidal interaction (likely with the cluster potential) and of ram pressure with the intracluster medium (ICM). These results can be used to gain more insights to the origin of S0s, dwarf and ultracompact dwarf (UCD) cluster galaxies.