Disentangling the Circumnuclear Environs of Centaurus A. I. High-Resolution Molecular Gas Imaging

Abstract

We present high resolution images of the 12 CO(2-1) emission in the central 1 ′ (1 kpc) of NGC 5128 (Centaurus A), observed using the Submillimeter Array. We elucidate for the first time the distribution and kinematics of the molecular gas in this region with a resolution of 6. ′′ 0 × 2. ′′ 4 (100 pc × 40 pc). We spatially resolve the circumnuclear molecular gas in the inner 24 ′′ × 12 ′′ (400 pc × 200 pc), which is elongated along a position angle P.A. ≃ 155 • and perpendicular to the radio/X-ray jet. The SE and NW components of the circumnuclear gas are connected to molecular gas found at larger radii. This gas appears as two parallel filaments at P.A. = 120 • , which are coextensive with the long sides of the 3 kiloparsec parallelogram shape of the previously observed dust continuum, as well as ionized and pure rotational H 2 lines. Spatial and kinematical asymmetries are apparent in both the circumnuclear and outer gas, suggesting non-coplanar and/or non-circular motions. We extend to inner radii (r < 200 pc) previously studied warped disk models built to reproduce the central parallelogram-shaped structure. Adopting the warped disk model we would confirm a gap in emission between the radii r = 200 -800 pc (12 ′′ -50 ′′ ), as has been suggested previously. Although this model explains this prominent feature, however, our 12 CO(2 − −1) observations show relevant deviations from this model. Namely, the physical connection between the circumnuclear gas and that at larger radii, brighter SE and NW sides on the parallelogram-shaped feature, and an outer curvature of its long sides. Overall it resembles more closely an S-shaped morphology, a trend that is also found in other molecular species. Hence, we explore qualitatively the possible contribution of a weak bi-symmetric potential which would naturally explain these peculiarities.

Centaurus A: morphology and kinematics of the atomic hydrogen

“…In addition, the model shows that in H i a gap in the distribution of the gas is present between 10 and ∼45 (from 0.2 to 0.8 kpc), confirming what was already found by other studies (e.g. Nicholson et al 1992;Quillen et al 1992Quillen et al , 2006Espada et al 2009) for the dust, molecular and ionised gas (e.g. Hα and CO).…”

“…Recently, Espada et al (2009) have modelled high-resolution CO data obtained with the SMA for the central kpc of Cen A and invoked the presence of a weak bar in these central regions. Interestingly, while their model seems to very poorly describe the jump in velocity observed in the CO velocity field at about 15 from the centre (see their Fig.…”

Resolving the Nucleus of Centaurus A at Mid-Infrared Wavelengths

“…Assuming that the dusty component is well represented by an inclined disk, our axis ratio of r ¼ 2.17 AE 0.17 can be interpreted as an inclination of cos À1 1/r ¼ 62.6 À2.6 þ2.18 and would then lie roughly in between the measurements of Neumayer et al (2007) and Espada et al (2009).…”

The Many Faces of the Gas in Centaurus A (NGC 5128)

“…The south-east and north-west components of the circumnuclear gas are connected to molecular gas found at larger radii, see Figure 8. Espada et al (2009) have extened the available models to the inner radii (r o 200 pc) in order to reproduce the central parallelogram-shaped structure observed in 12 CO(2-1), see Figure 8. Adopting the warped disk model, they confirmed a gap in emission between 200 and 800 pc radii, as mentioned above.…”