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

Abstract

We present high-resolution images of the 12CO(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 6farcs0 × 2farcs4 (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 of P.A. sime155° and perpendicular to the radio/X-ray jet. The southeast (SE) and northwest (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 kpc parallelogram shape of the previously observed dust continuum, as well as ionized and pure rotational H2 lines. Spatial and kinematical asymmetries are apparent in both the circumnuclear and outer gas, suggesting noncoplanar and/or noncircular 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 12CO(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 qualitatively explore the possible contribution of a weak bi-symmetric potential which would naturally explain these peculiarities.