Evidence for a disturbed velocity structure in the outer regions of the galaxy NGCÂ 1399 comes from a re-analysis of the planetary nebulae data from Arnaboldi et al .
( 1994 ) .
We find a strong rotation along a P.A.=140 ^ { \circ } for R \leq 140 ^ { \prime \prime } which is followed by a rapid drop off at larger radii , where the velocity dispersion starts to increase .
This kinematical behavior can be interpreted as an indication for an interaction scenario .
Interaction is advocated in previous analysis of the halo regions of this system , based on different dynamical tracers such as globular clusters and X-rays , but in all these studies the mass distribution is derived under the equilibrium hypothesis , which is not appropriate when an interaction takes place .
Here we attempt a non-equilibrium dynamical analysis of NGCÂ 1399 : with a simple model and under the impulse approximation , we show that the observed kinematics is consistent with an energy injection caused by a flyby encounter of NGCÂ 1399 with the nearby system NGCÂ 1404 .
In this approach , we find a mass-to-light ratio , M/L _ { \mathrm { B } } =26 M _ { \odot } / L _ { \odot } within R = 400 ^ { \prime \prime } , which is about half of that requested when equilibrium is assumed , i.e .
M/L _ { \mathrm { B } } =56 M _ { \odot } / L _ { \odot } .