This is the fourth paper of a series investigating the AGN fuelling/feedback processes in a sample of eleven nearby low-excitation radio galaxies (LERGs). In this paper we present follow-up Atacama Large Millimeter/submillimeter Array (ALMA) observations of one source, NGC3100, targeting the $^{ 12}$CO(1-0), $^{ 12}$CO(3-2), HCO$^{ +}$(4-3), SiO(3-2) and HNCO(6-5) molecular transitions. $^{ 12}$CO(1-0) and $^{ 12}$CO(3-2) lines are nicely detected and complement our previous $^{ 12}$CO(2-1) data. By comparing the relative strength of these three CO transitions, we find extreme gas excitation conditions (i.e. $T_{ \rm ex}\gtrsim50$ K) in regions that are spatially correlated with the radio lobes, supporting the case for a jet-ISM interaction. An accurate study of the CO kinematics demonstrates that, although the bulk of the gas is regularly rotating, two distinct non-rotational kinematic components can be identified in the inner gas regions: one can be associated to inflow/outflow streaming motions induced by a two-armed spiral perturbation; the second one is consistent with a jet-induced outflow with $v_{ \rm max}\approx 200$ km s$^{ -1}$ and $\dot{ M}\lesssim 0.12$ M$_{ \odot}$ yr$^{ -1}$. These values indicate that the jet-CO coupling ongoing in NGC3100 is only mildly affecting the gas kinematics, as opposed to what expected from existing simulations and other observational studies of (sub-)kpc scale jet-cold gas interactions. HCO$^{ +}$(4-3) emission is tentatively detected in a small area adjacent to the base of the northern radio lobe, possibly tracing a region of jet-induced gas compression. The SiO(3-2) and HNCO(6-5) shock tracers are undetected: this - along with the tentative HCO$^{ +}$(4-3) detection - may be consistent with a deficiency of very dense (i.e. $n_{ \rm crit} > 10^{ 6}$ cm$^{ -3}$) cold gas in the central regions of NGC3100.
Categories: astro-ph.GA