The rotating visible outflow in M 82

Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d'Hères, France

Corresponding author: greve@iram.fr

Received: 21 March 2003
Accepted: 26 November 2003

Abstract

M 82's minor axis outflow is seen at visible wavelengths as more or less regular hollow cones on both sides of the galactic disk. The outflowing material is expected to entrain the rotation, or part of the rotation, of the disk where the outflow originates. From the conservation of angular momentum it is furthermore expected that the outflowing material continues to rotate at large distances from the disk, although probably with smaller velocity because of radial divergence of the cones. We provide evidence of this kinematic picture from long-slit spectra of the cone wall H_α, [NII] and [SII] emission lines taken at ±20'' (±300 pc) and ~±40'' (~±600 pc) distance from the center and parallel to the minor axis, from data extracted from the literature, and from a cone model fit of the data. The angular momentum which is entrained in the outflow and eventually dissipated is a small fraction of the total angular momentum associated with the stars and gas in the central part of the disk. We compare our observation of the visible outflow with the outflow of dragged-out material investigated in mm-wavelength CO by other observers. It seems that the material observed at visible wavelengths is confined to narrow cones, and blows out at velocities larger than the escape velocity of the galaxy. The dragged-out material moves at slower velocities and on wider cones, and may fall back into the galaxy.