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The Skeleton of the Milky Way
  • Catherine Zucker,
  • Alyssa Goodman,
  • Cara Battersby
Catherine Zucker
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Alyssa Goodman
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Cara Battersby
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Abstract

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 (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. 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 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 p-p-v space; and exhibit no abrupt shifts in velocity. Evidence suggests that these candidates are marking the locations of significant spiral features, with the bone called filament 5 (”BC_18.88-0.09") 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.