Catherine Zucker edited sectionMethdology_To.tex  almost 9 years ago

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The name and coordinates for these ten filaments, along with their average LSR velocities, the number of bone criteria they satisfy, and a "quality rating" are listed in figure \ref{fig:candidates}. In figure \ref{fig:mass_of_bones}, we summarize physical parameters for all ten bone candidates, including estimates of distance, volume, mass, and aspect ratio. We calculate mass by \textit{estimating} an average H$_2$ column density of $2 \times 10^{22}$ cm$^{-2}$, consistent with the minimum IRDC peak column density to be included in the \citet{Peretto_2009} catalog of 11,303 IRDCs. We calculate distances assuming all of our bone candidates (see Figure \ref{fig:skeleton}) are associated with the \citet{Dame_2011} Scutum-Centaurus arm. When available, we also provide distance measurements from the \citet{Ellsworth_Bowers_2013} catalog, which provides distances to 1710 molecular clouds from the BGPS survey, derived using a Bayesian distance probability density function.   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, \textbf{filament 1 ("BC\_026.94-0.30"), filament 2 ("BC\_025.24-0.45"), filament 5 ("BC\_018.88-0.09"), filament 7 ("BC\_04.14-0.02"), filament 9 ("BC\_335.31-0.29"),  and BC\_332.21-0.04}, filament 10 ("BC\_332.21-0.04")},  to varying degrees of excellence. We note that BC\_332.21-0.04 filament 10  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, filament 9,  even though it has a $p-v$ orientation perpendicular to predicted fits of the Scutum-Centaurus arm (see Figure \ref{fig:skeleton}). As spurs and inter-arm structures are likely to lie close to the physical Galactic mid-plane, but with velocity gradients angled with respect to predicted arm fits, we do {\it not} require that a bone be parallel to arm $p-v$ traces, so as not to exclude potential spurs, feathers, or other inter-arm features. Of the four remaining filaments that do not meet all six criteria---BC\_357.62-0.33, BC\_11.13-0.12, BC\_24.96-0.17, BC\_21.25-0.15 and---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 of all our candidates in a follow-up study, accounting for expected projection effects if they lie along the nearest spiral arm. The first of these candidates, BC\_357.62-0.33, shows particular promise, lying within 2-3 pc of the physical Galactic midplane and tracing a prominent peak of CO emission in both \textit{p-p} and \textit{p-v} space (see appendix section BC\_357.62-0.33). The second 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, also tracing a prominent peak of CO emission in \textit{p-v} space (see appendix section BC\_11.13-0.12). The remaining two filaments, BC\_24.96-0.17, BC\_21.25-0.15 are both awarded a quality rating of "C." BC\-024.96-0.17 lies 10 km/s from the \citet{Shane_1972} fit to HI for the Scutum-Centaurus arm (at the upper limit of criterion 4) while BC\_021.25-0.15 appears to be a potential interarm filament, lying between the Scutum-Centaurus and Norma-4kpc arms in \textit{p-v}. We also note a small break in the extinction feature of BC\_021.25-0.15, though the filament has been confirmed to be contiguous in velocity space as traced by $^{13}\rm{CO}$ from the GRS Survey.