Highly supersonic motions within the outer features of the Eta Carinae nebulosity

Abstract

Spatially resolved H$α$ and [N{\sc ii}] line profiles have been obtained over striking features in the outer regions of the Eta Carinae nebula. The highly irregular outer `shell' of low ionization, [N{\sc ii}] bright, knots has been shown to exhibit radial velocities between -1200 and +300 km/s with respect to the systemic radial velocity, over its perimeter. Furthermore, several knots have been found which appear to emit only in the H$α$ line with radial velocities up to -1450 km/s. However, the most intriguing features are a narrow `spike' that projects through this outer shell and a faint `arc' of emission that extends well beyond it. The `spike', which exhibits a change of radial velocity along its length, could be a narrow collimated jet with an outflow velocity of > 1000 km/s. In one interpretation the `arc' is modelled by a conical outflow and mechanisms for generating [N{\sc ii}] emission from highly supersonic gas are also discussed.