Insights About Induced SFR in the Shell Systems of Early-Type Galaxies from UV (GALEX)

Current views consider shell structures as a debris of recent minor/major merging event though also weak interaction models could produce long lasting shells on host galaxies possessing a stellar thick disc. Recent optical observations suggest an external origin of the matter, as predicted by merging models. At the same time, a set of observations showing a clear association between cold (HI/CO) gas and stars challenges present merging models In this framework we will present Galex observations of a well selected sample of shell galaxies chosen among those with detected HI and/or CO both in the main body of the galaxy and interleaved with shells. With these data we will show whether the HI/CO gas rich shells host ongoing star formation processes and we will give independent indications: (1) about the present day star formation; (2) if their presence or absence is consistent with the kinematics of the ionised gas, (3) address merging models which fails in reproducing a coupling between stellar and gaseous shells.