Catherine Zucker edited sectionMethdology_To.tex  about 9 years ago

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Of the four remaining filaments that do not meet 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 $\ge 50:1$). 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. We plan to examine the the aspect ratios (minus projection effects) of all our candidates in a follow-up study. 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 (see appendix), though BC\_24.96-0.17 does like at the upper limit of criterion 4. The third filament, BC\_11.13-0.12 ("the snake"), has already been well-studied from a star formation perspective, hosting over a dozen protostellar cores likely to produce regions of high-mass star formation \citep{Wang_2014,Henning_2010}. From a Galactic bone perspective, the snake strongly satisfies all criteria except number 6--it lies within 15 pc of the physical galactic midplane and 5 km/s from the \citet{Dame_2011} Scutum-Centaurus global-log fit to CO, tracing a prominent peak of the Scutum-Centaurus arm in p-v space (see appendix section BC\_11.13-0.12). Our weakest bone candidate is BC\_21.25-0.15, the only filament to receive a quality grade of "C".   In summary, it is important to emphasize 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, since criterion 6 does not allow for projection effects in imposing an aspect ratio limit, bones which otherwise meet all criteria could fail if they are oriented more perpendicular with respect to the sun. 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. An comprehensive analysis of all ten bone candidates can be found in the appendix.