the disc potential.

In this paper, we consider two <span style="font-variant:small-caps;">galactics</span> models. The first (Model 1) is from @widrow2008. In that paper, Bayesian and Markov chain Monte Carlo methods were used to constrain the <span style="font-variant:small-caps;">galactics</span> parameters so as to match kinematic and photometric observations of the Milky Way. That analysis yielded a suite of models that varied in their susceptibility to bar formation. The model that we chose for this paper has a relatively weak bar instability. For Model 2, we reduced the disc mass by roughly a third and increased the masses of the bulge and halo components so as to obtain a similar rotation curve. The disc in Model 2 is therefore so light that it never forms a bar.

While our models yield very similar circular speed curves they differ in the relative contributions of the disc and the dynamically hot components (the bulge and halo) to the radial force, as shown in Fig. \[fig:circspeed\]. In particular, Model 1 has a disc mass of $M_d \approx 4 \times 10^{10}\,M_\odot$, which impies that at a radius of $2.2\,R_d$, $V_d^2/V_c^2 = 0.51$, where $V_c = V_c(R)$ is the circular speed at radius $R$ and $V_d$ is the contribution 