Catherine Zucker edited sectionMethdology_To.tex  about 9 years ago

Commit id: 1531417378b72bf36131d861cef28f6be233780c

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Of the ten filaments with velocities consistent with galactic rotation, \textbf{six} of these meet all six bone criteria: \textbf{BC\_26.94-0.30, BC\_25.24-0.45,BC\_18.88-0.09, BC\_4.14-0.02, BC\_335.31-0.29, and BC\_332.21-0.04}, to varying degrees of excellence. We note that BC\_332.21-0.04 has likely been disrupted by stellar feedback, making its aspect ratio and velocity structure more difficult to define. Since we predict that all galactic bones will likely be destroyed by stellar feedback and/or galactic shear, we include it here as part of a larger attempt to build a catalog of bones at all stages of their evolution. We also include BC\_335.31-0.29, despite a velocity structure tangential to predicted fits of the Scutum-Centaurus arm. As spurs and interarm structures are likely to lie close to the physical Galactic midplane, but with velocity gradients angled with respect to predicted arm fits, we also include this filament in attempt to classify all bones potentially aligned with Galactic structure---be it spiral arms, spurs, feathers, or interarm regions.   Of the four remaining  filaments that do not meet the all  six criteria--BC\_24.96-0.17, BC\_21.25-0.15, BC\_11.13-0.12, and BC\_357.62-0.33--all of them fail criterion 6 (aspect ratio $\gte$ 50:1). $\ge 50:1$). As our criterion 6 does not allow for projection effects in imposing an aspect ratio limit, we emphasize that those filaments lying more tangential to our line-of-sight will appear foreshortened, and could very well meet the 50:1 minimum limit if projection effects were removed. Two of these filaments BC\_24.96-0.17 and BC\_357.62-0.33 show particular promise, both lying within 1-2 pc of the physical Galactic midplane.  Thus, it is important to note that some of the above criteria will likely be modified in the long run, as we learn more about the Skeleton of the Milky Way. Given our limited a priori knowledge of the Galaxy's structure, it is presently easier to confirm Bones that are spine-like, lying along arms with velocities predicted by extant modeling (criteria 1, 5), and harder to find spurs off those arms or inter-arm features (e.g. BC\_335.31-0.29), the velocities of which are hard to predict well. Similarly, criterion 6 \textitdoes not allow for projection effects in imposing an aspect ratio limit. As we learn more about spiral structure from simulations and modeling, these criteria will also be adjusted to allow for Bone-like features that represent spurs, inter-arm structures, and/or foreshortened structures lying close to our line of sight.