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The Skeleton of the Milky Way (Fall 2014 Draft)
  • Catherine Zucker,
  • Cara Battersby,
  • Alyssa Goodman
Catherine Zucker
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Cara Battersby
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Alyssa Goodman
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Abstract

Recently, \citet{Goodman_2014} argued that a 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.“ We present the first evidence of 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 midplane. We use \(\textrm{CO}\), \(\mathrm{N_2H+}\), \(\textrm{HCO}^{+}\) and \(\mathrm{NH_3}\) radial velocity data to establish the location of the candidates in p-p-v space. Of the ten filaments, six candidates 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 Nessie-like filaments which mark the location of significant spiral features, with ”filament 5" replicating Nessie’s properties most strongly. 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.