Alyssa Goodman Small changes to address Cara's stylistic points.  about 9 years ago

Commit id: 258f330dcf6c36ff9d76897058b78eedd1da3404

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Recently, \citet{Goodman_2014} argued that the very long, very thin infrared dark cloud "Nessie" lies directly in the Galactic midplane and runs along the Scutum-Centaurus arm in position-position-velocity ({\it p-p-v}) space as traced by lower density $\textrm{CO}$ and higher density $\mathrm{NH_3}$ gas. Nessie was presented as the first "bone'' of the Milky Way, an extraordinarily long, thin, high-contrast filament that can be used to map our Galaxy's "skeleton." Here, we present evidence for additional bones in the Milky Way Galaxy, arguing that Nessie is not a curiosity but one of several filaments that could potentially trace Galactic structure. Our ten bone candidates are all long, filamentary, mid-infrared extinction features which lie parallel to, and no more than twenty parsecs from, the physical Galactic mid-plane (assuming a flat Galaxy). We use $\textrm{CO}$, $\mathrm{N_2H+}$, $\textrm{HCO}^{+}$ and $\mathrm{NH_3}$ radial velocity data to establish the three-dimensional location of the candidates in {\it p-p-v} space. Of the ten candidates, six also: have a projected aspect ratio of $\ge 50\colon1$; run along, or extremely close to, the Scutum-Centaurus arm in \textit{p-p-v} space; {\it and} exhibit no abrupt shifts in velocity. Evidence suggests that these candidates are Galactic bones which mark bones, marking  the location locations  of significant spiral features, with the bone called ``BC\_18.88-0.09" replicating Nessie's properties most strongly. being a close analog to Nessie in the Northern Sky.  As molecular spectral-line and extinction maps cover more of the sky at increasing resolution and sensitivity, we seek to find more bones in future studies, ultimately to create a global-fit to the Galaxy's spiral arms by piecing together individual skeletal features.