Atomic-to-molecular gas phase transition triggered by the radio jet in
  Centaurus A
  NGC 5128 (Centaurus A) is one of the best example to study AGN-feedback in
the local Universe. At 13.5 kpc from the galaxy, optical filaments with recent
star formation are lying along the radio-jet direction. We used the Atacama
Pathfinder EXperiment (APEX) to map the CO(2-1) emission all along the
filaments structure. Molecular gas mass of 8.2x10^7 Msun was found over the 4.2
kpc-structure which represents about 3% of the total gas mass of the NGC 5128
cold gas content. Two dusty mostly molecular structures are identified,
following the optical filaments. The region corresponds to the crossing of the
radio jet with the northern HI shell, coming from a past galaxy merger. One
filament is located at the border of the HI shell, while the other is entirely
molecular, and devoid of HI gas. The molecular mass is comparable to the HI
mass in the shell, suggesting a scenario where the atomic gas was shocked and
transformed in molecular clouds by the radio jet. Comparison with combined FIR
Herschel and UV GALEX estimation of star formation rates in the same regions
leads to depletion times of more than 10 Gyr. The filaments are thus less
efficient than discs in converting molecular gas into stars. Kinetic energy
injection triggered by shocks all along the jet/gas interface is a possible
process that appears to be consistent with MUSE line ratio diagnostics derived
in a smaller region of the northern filaments. Whether the AGN is the sole
origin of this energy input and what is the dominant (mechanical vs radiative)
mode for this process is however still to be investigated.
