We present the orbital analysis of four response models , that succeed in reproducing morphological features of NGC 1300 .
Two of them assume a planar ( 2D ) geometry with \Omega _ { p } =22 and 16 km s ^ { -1 } kpc ^ { -1 } respectively .
The two others assume a cylindrical ( thick ) disc and rotate with the same pattern speeds as the 2D models .
These response models reproduce most successfully main morphological features of NGC 1300 among a large number of models , as became evident in a previous study .
Our main result is the discovery of three new dynamical mechanisms that can support structures in a barred-spiral grand design system .
These mechanisms are presented in characteristic cases , where these dynamical phenomena take place .
They refer firstly to the support of a strong bar , of ansae type , almost solely by chaotic orbits , then to the support of spirals by chaotic orbits that for a certain number of pattern revolutions follow an n:1 ( n=7,8 ) morphology , and finally to the support of spiral arms by a combination of orbits trapped around L _ { 4 , 5 } and sticky chaotic orbits with the same Jacobi constant .
We have encountered these dynamical phenomena in a large fraction of the cases we studied as we varied the parameters of our general models , without forcing in some way their appearance .
This suggests that they could be responsible for the observed morphologies of many barred-spiral galaxies .
Comparing our response models among themselves we find that the NGC 1300 morphology is best described by a thick disc model for the bar region and a 2D disc model for the spirals , with both components rotating with the same pattern speed \Omega _ { p } =16 km s ^ { -1 } kpc ^ { -1 } .
In such a case , the whole structure is included inside the corotation of the system .
The bar is supported mainly by regular orbits , while the spirals are supported by chaotic orbits .