Abstract

The energy released by an active galactic nucleus (AGN) has a strong impact on the surrounding interstellar medium (ISM). The important role for galaxy evolution of these energetic feedback effects has been supported, in recent years, by the discovery of massive gas outflows in a growing number of galaxies with AGN . Even more interesting has been the realisation that the dominant component of these AGN -driven outflows appears to be associated with cold (atomic and/or molecular) gas. I will present recent results obtained from HI and CO observations of a number of objects where the radio jet is playing a major role in producing large and fast gas outflows. The results are reinforcing the conclusion that gas outflows have a complex and multiphase structure and that cold gas in different phases (atomic and molecular) represents a major component. High-spatial resolution observations have allowed, in a number of sources, to locate the region where the outflow originates as well as to derive more accurate estimates of the mass outflow rate and the associated energy. Therefore, these results provide important constraints for understanding the mechanisms that lie at the origin out the outflows. A possible link between the evolutionary stage of the radio source and the presence of cold gas and outflows will also be discussed. This is explored using observations at low frequency (LOFAR), to trace past phases of activity combined with HI observations. The latter are part of a campaign of preparatory work for Apertif, the phased array feeds system upgrade of the Westerbork radio telescope. I will give an update on the results obtained so far.