Volume 599, March 2017
|Number of page(s)||14|
|Published online||28 February 2017|
The outflow of gas from the Centaurus A circumnuclear disk
Atomic spectral line maps from Herschel/PACS and APEX
1 Sterrewacht Leiden, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
4 I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
Received: 25 July 2016
Accepted: 26 October 2016
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 60 km s-1 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 < 90 pc) is bright in [OI], [OIII], and [CII]; [OI] λ63 μm 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 100 cm-3) and low everywhere else. Neutral gas densities range from 4000 cm-3 (outflow, extended thin disk ETD) to 20 000 cm-3 (CND). The CND radiation field (Go ≈ 4) is weak compared to the ETD starburst field (Go ≈ 40). The outflow has a much stronger radiation field (Go = 130). The total mass of all the CND gas is 9.1 ± 0.9×107M⊙ 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 ≈ 2 M⊙ yr-1, 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.
Key words: galaxies: individual: Centaurus A (NGC 5128) / galaxies: active / galaxies: elliptical and lenticular, cD / galaxies: nuclei / galaxies: ISM / ISM: jets and outflows
© ESO, 2017
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