Skeleton new

Catherine Zucker

and 2 more

Recently, 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 CO and higher density NH₃ 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 CO, N₂H+, HCO+ and NH₃ 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 ≥50: 1; 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.
Glue

Catherine Zucker

and 2 more

Recently, 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 CO and higher density NH₃ 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 CO, N₂H+, HCO+ and NH₃ 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 ≥50: 1, 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.
Candid5 pos vel

Cara Battersby

and 18 more

It has recently been proposed (Goodman et al. 2014) that long, skinny, infrared dark clouds may trace out the densest features of the Milky Way, which include spiral arms, and possible inter-arm tendrils. The features are so long and skinny that they are almost certainly caused and maintained by a global gravitational potential, so they are not likely to be self-gravitating molecular clouds. These “Bones of the Milky Way” could be used to help piece together the structure of the Galaxy, shedding light on age-old questions, such as the number of spiral arms in our Galaxy and their locations. We have searched for and identified a handful of candidate Bones: long, filamentary infrared-dark clouds found in position-velocity space where our current model of the Galaxy predicts spiral arms should lie. Utilizing archival data, we have confirmed the location of these Bone candidates in the Galactic mid-plane and within 5 km/s of a spiral arm. We propose to use the IRAM 30-m to create the first ever high-resolution CO map (1mm) of a candidate “Bone of the Milky Way,” simultaneously with a suite of dense gas tracers at 3mm with IRAM. Capitalizing on IRAM’s unique ability to map CO over large areas at high angular resolution while simultaneously obtaining kinematic information about the dense gas, we will provide the first measure of structure and kinematics toward these unique Galactic structures. Our total time request is XX hours to map XX sq. arcminutes at 1mm (¹³CO and C¹⁸O 2-1) and 3mm (HCO+, HCN 1-0, etc.) toward our most promising Northern-hemisphere candidate Bone, “BC1.”