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 } \mathrm { M } _ { \sun } , scale length 2.0 \leq R _ { d } \leq 2.9 kpc , LSR circular velocity 222 \leq \Theta _ { 0 } \leq 233 \mathrm { km } \mathrm { s } ^ { -1 } , and solar circle stellar surface density 34 \leq \Sigma _ { d } ( R _ { 0 } ) \leq 61 \mathrm { M } _ { \sun } \mathrm { 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 \mathrm { km } \mathrm { s } ^ { -1 } \mathrm { 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 \mathrm { M } _ { \sun } \mathrm { pc } ^ { -3 } ( 0.34 \mathrm { GeV } \mathrm { 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 .