A warped accretion disk and wide-angle outflow in the inner parsec of the Circinus galaxy
Greenhill, LJ and Booth, RS and Ellingsen, SP and Herrnstein, JR and Jauncey, DL and McCulloch, PM and Moran, JM and Norris, RP and Reynolds, JE and Tzioumis, AK, A warped accretion disk and wide-angle outflow in the inner parsec of the Circinus galaxy, The Astrophysical Journal, 590, (1 I) pp. 162-173. ISSN 0004-637X (2003) [Refereed Article]
We present the first VLBI maps of H 2O maser emission (λ1.3 cm) in the nucleus of the Circinus galaxy, constructed from data obtained with the Australia Telescope Long Baseline Array. The maser emission traces a warped, edge-on accretion disk between radii of 0.11 ± 0.02 and ∼0.40 pc, as well as a wide-angle outflow that extends up to ∼1 pc from the estimated disk center. The disk rotation is close to Keplerian (v α r -0.5), the maximum detected rotation speed is 260 km s -1, and the inferred central mass is (1.7 ± 0.3) × 10 6 M ⊙. The outflowing masers are irregularly distributed above and below the disk, with relative outflow velocities up to ∼±160 km s -1, projected along the line of sight. The flow probably originates closer than 0.1 pc to the central engine, possibly in an inward extension of the accretion disk, although there is only weak evidence of rotation in the outward-moving material. We observe that the warp of the disk appears to collimate the outflow and to fix the extent of the ionization cone observed on larger angular scales. This study provides the first direct evidence (i.e., through imaging) of dusty, high-density, molecular material in a nuclear outflow less than 1 pc from the central engine of a Seyfert galaxy, as well as the first graphic evidence that warped accretion disks can channel outflows and illumination patterns in active galactic nuclei. We speculate that the same arrangement, which in some ways obviates the need for a geometrically thick, dusty torus, may apply to other type 2 active galactic nuclei.