We provide the first quantitative evidence for the deceleration/growth of the Galactic bar from local stellar kinematics thus confirming dynamical friction within expectations for a typical dark matter halo .
The kinematic response of the stellar disk to a decelerating bar is studied using secular perturbation theory and test particle simulations .
We show that the velocity distribution at any point in the disk affected by a naturally slowing bar is qualitatively different from that perturbed by a steadily rotating bar with the same current pattern speed \Omega _ { p } and amplitude .
When the bar slows with rate \dot { \Omega } _ { p } , its resonances sweep through phase space .
Depending on \dot { \Omega } _ { p } , they trap and drag along a portion of previously free orbits .
This enhances occupation on resonances , but also changes the distribution of stars within the resonant region .
Helped by this accumulation of orbits near the boundary of the resonant region , the decelerating bar model reproduces with its corotation resonance the offset and strength of the Hercules stream in the local v _ { R } - v _ { \varphi } plane and the double-peaked structure of \bar { v } _ { R } in the L _ { z } - \varphi plane .
On the outer/inner Lindblad resonances and other higher order resonances , resonant dragging by a slowing bar is associated with a continuing increase in radial action .
We compare the model to data in the action plane , identifying multiple resonance ridges .
This work shows models using a constant bar pattern speed ( \dot { \Omega } _ { p } = 0 ) likely lead to qualitatively wrong conclusions .
Most importantly we provide the first quantitative estimate of the slowing rate of the bar : \dot { \Omega } _ { p } = ( -5.0 \pm 2.5 ) { km } { s } ^ { -1 } { kpc } ^ { -1 } { % Gyr } ^ { -1 } .