The AGN fueling/feedback cycle in LERGs. A multi-phase study of a sample of nearby radio galaxies

Feedback associated with active galactic nuclei (AGN) can potentially play a role in shaping galaxies over cosmic time, by changing the physical conditions of the surrounding inter-stellar medium (ISM) or expelling it from the nuclear regions, thus impacting the star formation processes and the subsequent evolution of the host galaxy. The many details of such process, however, still remain poorly understood. Here we present the results obtained so far by analyzing ALMA Cycle 3 CO(2-1) and continuum observations of 9 lowexcitation radio galaxies (LERGs) in the southern sky. LERGs are a class of radio galaxies characterized by low accretion rates (<<0.01MEdd) and their feedback is almost entirely kinetic (i.e. jet-induced). The powering mechanism of these objects is still uncertain. Our work shows that (sub-)kpc rotating molecular discs are very common in LERGs (6 out of 9 sources detected in CO). Although signs of warps or asymmetries (i.e. gas not fully relaxed) are clearly visible in some of the detected discs, the bulk of the gas appears to be in ordered rotation (at least at the resolution of our ALMA observations). It is then likely that most of the cold gas in LERGs is in stable orbits, consistently with a relatively low accretion rate. Whenever possible, we also demonstrated that the CO discs are co-spatial with dust discs/lanes. In a couple of cases the gas shows kinematic misalignment with respect to the stellar component, pointing towards an external origin of the gas. The 3D modeling of the six CO discs indicates the presence of perturbations and/or radial motions in all the cases. In most of them, however, the spatial resolution of the observations does not allow us to draw strong conclusions. In our best resolved case (NGC 3100) the CO structure is disrupted in the direction of the northern jet, likely indicating a jet/ gas interaction. Furthermore, we find indications for non-negligible radial motions in the plane of the CO disc. This is likely consistent with the presence of inflow/outflow streaming motions associated with the spiral pattern that we observe at the centre of the CO disc