The second data release of the Gaia mission has revealed a very rich structure in local velocity space .
In terms of in-plane motions , this rich structure is also seen as multiple ridges in the actions of the axisymmetric background potential of the Galaxy .
These ridges are probably related to a combination of effects from ongoing phase-mixing and resonances from the spiral arms and the bar .
We have recently developed a method to capture the behaviour of the stellar phase-space distribution function at a resonance , by re-expressing it in terms of a new set of canonical actions and angles variables valid in the resonant region .
Here , by properly treating the distribution function at resonances , and by using a realistic model for a slowly rotating large Galactic bar with pattern speed \Omega _ { \mathrm { b } } = 39 ~ { } ~ { } \mathrm { km } ~ { } \mathrm { s } ^ { -1 } ~ { } \mathrm { kpc } ^ { -1 } , we show that no less than six ridges in local action space can be related to resonances with the bar .
Two of these at low angular momentum correspond to the corotation resonance , and can be associated to the Hercules moving group in local velocity space .
Another one at high angular momentum corresponds to the outer Lindblad resonance , and can tentatively be associated to the velocity structure seen as an arch at high azimuthal velocities in Gaia data .
The other ridges are associated to the 3:1 , 4:1 and 6:1 resonances .
The latter can be associated to the so-called ‘ horn ’ of the local velocity distribution .
While it is clear that effects from spiral arms and incomplete phase-mixing related to external perturbations also play a role in shaping the complex kinematics revealed by Gaia data , the present work demonstrates that , contrary to common misconceptions , the bar alone can create multiple prominent ridges in velocity and action space .