Does the Milky Way Have a Maximal Disk?

The Milky Way is often considered to be the best example of a spiral forwhich the dark matter not only dominates the outer kinematics, but also plays amajor dynamical role in the inner galaxy: the Galactic disk is therefore saidto be ``sub-maximal.'' This conclusion is important to the understanding of theevolution of galaxies and the viability of particular dark matter models. TheGalactic evidence rests on a number of structural and kinematic measurements,many of which have recently been revised. The new constraints indicate not onlythat the Galaxy is a more typical member of its class (Sb-Sc spirals) thanpreviously thought, but also require a re-examination of the question ofwhether or not the Milky Way disk is maximal. By applying to the Milky Way thesame definition of ``maximal disk'' that is applied to external galaxies, it isshown that the new observational constraints are consistent with a Galacticmaximal disk of reasonable $M/L$. In particular, the local disk column can besubstantially less than the oft-quoted required $\Sigma_{\odot} \approx 100\msolar pc^{-2}$ - as low as $40 \msolar pc^{-2}$ in the extreme case - andstill be maximal, in the sense that the dark halo provides negligible rotationsupport in the inner Galaxy. This result has possible implications for anyconclusion that rests on assumptions about the potentials of the Galactic diskor dark halo, and in particular for the interpretation of microlensing resultsalong both LMC and bulge lines of sight.Comment: Accepted for publication in The Astrophysical Journal. 23 Latex-generated pages, one (new) table, three figures (two new). A few additions to the bibliography, an expanded discussion, and slight quantitative changes, none of which affect the conclusion