The Biconical Outflow in the Seyfert Galaxy NGC 2992

Abstract

We report on a detailed kinematic study of the galactic-scale outflow in the Seyfert galaxy NGC 2992. The TAURUS-2 imaging Fabry-Perot interferometer was used on the 3.9 m Anglo-Australian Telescope to derive the two-dimensional velocity field of the Hα-emitting gas over the central arcminute of NGC 2992. The complete two-dimensional coverage of the data combined with simple kinematic models of rotating axisymmetric disks allow us to differentiate the outflowing material from the line-emitting material associated with the galactic disk. The kinematics of the disk component out to R = 3.0 kpc are well modeled by pure circular rotation in a plane inclined at i = 68° ± 3° from the plane of the sky and with kinematic major axis along P.A. = 32° ± 3°. The outflow component is distributed into two wide cones with opening angle ≈125°–135° and extending ~2.8 kpc (18'') on both sides of the nucleus at nearly right angles ( ≈ 116° ± 5°) to the disk kinematic major axis. The outflow on the southeastern side of the nucleus is made of two distinct kinematic components interpreted as the front and back walls of a cone. The azimuthal velocity gradient in the back-wall component reflects residual rotational motion, which indicates either that the outflowing material was lifted from the disk or that the underlying galactic disk is contributing slightly to this component. A single outflow component is detected in the northwestern cone. A biconical outflow model with velocities ranging from 50 to 200 km s-1 and oriented nearly perpendicular to the galactic disk can explain the data. The broad-line profiles and asymmetries in the velocity fields suggest that some of the entrained line-emitting material may lie inside the biconical structure rather than only on the surface of the bicone. The mass involved in this outflow is of order ~1 × 107 n M⊙, and the bulk and turbulent kinematic energies are ~6 × 1053 n ergs and ~3 × 1054 n ergs, respectively. The most likely energy source is a hot, bipolar, thermal wind powered on a subkiloparsec scale by the active galactic nucleus and diverted along the galaxy's minor axis by the pressure gradient of the ISM in the host galaxy. The data are not consistent with a starburst-driven wind or a collimated outflow powered by radio jets.