2017A&A...599A..53I

The physical state of the gas in the central 500 pc of NGC 5128 (the radio galaxy Centaurus A), was investigated using the fine-structure lines of carbon [CI], [CII]; oxygen [OI], [OIII], and nitrogen [NII], [NIII] as well as the ¹²CO(4-3) molecular line. The circumnuclear disk (CND) is traced by emission from dust and the neutral gas ([CI] and ¹²CO). A gas outflow with a line-of-sight velocity of 60km/s is evident in both lines. The [CI] emission from the CND is unusually strong with respect to that from CO. The center of the CND (R<90pc) is bright in [OI], [OIII], and [CII]; [OI] λ63µm emission dominates that of [CII] even though it is absorbed with optical depths τ=1.0-1.5. The outflow is well-traced by the [NII] and [NIII] lines and also seen in the [CII] and [OIII] lines that peak in the center. Ionized gas densities are highest in the CND (about 100cm^–3) and low everywhere else. Neutral gas densities range from 4000cm^–3 (outflow, extended thin disk ETD) to 20000cm^–3 (CND). The CND radiation field (G_o~=4) is weak compared to the ETD starburst field (G_o~=40). The outflow has a much stronger radiation field (G_o=130). The total mass of all the CND gas is 9.1±0.9x10⁷M_☉ but the mass of the outflowing gas is only 15-30% of that. The outflow most likely originates from the shock-dominated CND cavity surrounding the central black hole. With a factor of three uncertainty, the mass outflow rate is ~=2M_☉/yr, a thousand times higher than the accretion rate of the black hole. Without replenishment, the CND will be depleted in 15-120 million years. However, the outflow velocity is well below the escape velocity.