Cold gas and the disruptive effect of a young radio jet
  Newly born and young radio sources are in a delicate phase of their life.
Their jets are fighting their way through the surrounding gaseous medium,
strongly experiencing this interaction while, at the same time, impacting and
affecting the interstellar medium (ISM). Here we present the results from two
studies of HI (in absorption) and molecular gas illustrating what can be
learned from these phases of the gas. We first describe a statistical study
with the WSRT. The study shows that the young radio sources not only have an
higher detection rate of HI, but also systematically broader and more
asymmetric HI profiles, most of them blueshifted. This supports the idea that
we are looking at young radio jets making their way through the surrounding
ISM, which also appears to be, on average, richer in gas than in evolved radio
sources. Signatures of the impact of the jet are seen in the kinematics of the
gas. However, even among the young sources, we identify a population that
remains undetected in HI even after stacking their profiles. Orientation
effects can only partly explain the result. These objects either are genuinely
gas-poor or have different conditions of the medium, e.g. higher spin
temperature. We further present the ALMA study of molecular gas in IC5063 to
trace in detail the jet impacting the ISM. The kinematics of the cold,
molecular gas co-spatial with the radio plasma shows this process in action.
The ALMA data reveal a fast outflow of molecular gas extending along the entire
radio jet (~1 kpc), with the highest outflow velocities at the location of the
brighter hot-spot. We propose a scenario where the radio jet is expanding into
a clumpy medium, interacting directly with the clouds and inflating a cocoon
that drives a lateral outflow into the ISM.
