The Surface Density Profile of the Galactic Disk from the Terminal
  Velocity Curve
  The mass distribution of the Galactic disk is constructed from the terminal
velocity curve and the mass discrepancy-acceleration relation. Mass models
numerically quantifying the detailed surface density profiles are tabulated.
For $R_0 = 8$ kpc, the models have stellar mass $5 < M_* < 6 \times 10^{10}$
M$_{\odot}$, scale length $2.0 \le R_d \le 2.9$ kpc, LSR circular velocity $222
\le \Theta_0 \le 233$ km s$^{-1}$, and solar circle stellar surface density $34
\le \Sigma_d(R_0) \le 61$ M$_{\odot}$ pc$^{-2}$. The present inter-arm location
of the solar neighborhood may have a somewhat lower stellar surface density
than average for the solar circle. The Milky Way appears to be a normal spiral
galaxy that obeys scaling relations like the Tully-Fisher relation, the
size-mass relation, and the disk maximality-surface brightness relation. The
stellar disk is maximal, and the spiral arms are massive. The bumps and wiggles
in the terminal velocity curve correspond to known spiral features (e.g., the
Centaurus Arm is a $\sim 50\%$ overdensity). The rotation curve switches
between positive and negative over scales of hundreds of parsecs. The rms
amplitude $\langle$$|$$dV/dR$$|^2$$\rangle$$^{1/2} \approx 14$ km s$^{-1}$
kpc$^{-1}$, implying that commonly neglected terms in the Jeans equations may
be non-negligible. The spherically averaged local dark matter density is
$\rho_{0,DM} \approx 0.009$ M$_{\odot}$ pc$^{-3}$ (0.3 GeV cm$^{-3}$).
Adiabatic compression of the dark matter halo may help reconcile the Milky Way
with the $c$-$V_{200}$ relation expected in $\Lambda$CDM while also helping to
mitigate the too big to fail problem, but it remains difficult to reconcile the
inner bulge/bar dominated region with a cuspy halo. We note that NGC 3521 is a
near twin to the Milky Way, having a similar luminosity, scale length, and
rotation curve.
