Centaurus A , with its gas-rich elliptical host galaxy , NGC 5128 , is the nearest radio galaxy at a distance of 3.8 Mpc .
Its proximity allows us to study the interaction between an active galactic nucleus , radio jets , and molecular gas in great detail .
We present ALMA observations of low J transitions of three CO isotopologues , HCN , HCO ^ { + } , HNC , CN , and CCH toward the inner projected 500 pc of NGC 5128 .
Our observations resolve physical sizes down to 40 pc .
By observing multiple chemical probes , we determine the physical and chemical conditions of the nuclear interstellar medium of NGC 5128 .
This region contains molecular arms associated with the dust lanes and a circumnuclear disk ( CND ) interior to the molecular arms .
The CND is approximately 400 pc by 200 pc and appears to be chemically distinct from the molecular arms .
It is dominated by dense gas tracers while the molecular arms are dominated by ^ { 12 } CO and its rare isotopologues .
The CND has a higher temperature , elevated CN/HCN and HCN/HNC intensity ratios , and much weaker ^ { 13 } CO and C ^ { 18 } O emission than the molecular arms .
This suggests an influence from the AGN on the CND molecular gas .
There is also absorption against the AGN with a low velocity complex near the systemic velocity and a high velocity complex shifted by about 60 km s ^ { -1 } .
We find similar chemical properties between the CND in emission and both the low and high velocity absorption complexes implying that both likely originate from the CND .
If the HV complex does originate in the CND , then that gas would correspond to gas falling toward the supermassive black hole .