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Large scale filaments associated with Milky Way spiral arms

Large scale filaments associated with Milky Way spiral arms

Publication date: 29 May 2015

Authors: Ke Wang et al.

Journal: Monthly Notices of the Royal Astronomical Society
Volume: 450
Issue: 4
Page: 4043
Year: 2015

Copyright: The Royal Astronomical Society

The ubiquity of filamentary structure at various scales throughout the Galaxy has triggered a renewed interest in their formation, evolution, and role in star formation. The largest filaments can reach up to Galactic scale as part of the spiral arm structure. However, such large-scale filaments are hard to identify systematically due to limitations in identifying methodology (i.e. as extinction features). We present a new approach to directly search for the largest, coldest, and densest filaments in the Galaxy, making use of sensitive Herschel Hi-GAL (Herschel Infrared Galactic Plane Survey) data complemented by spectral line cubes. We present a sample of the nine most prominent Herschel filaments, including six identified from a pilot search field plus three from outside the field. These filaments measure 37–99 pc long and 0.6–3.0 pc wide with masses (0.5–8.3) × 104 MSun, and beam-averaged (28 arcsec, or 0.4–0.7 pc) peak H2 column densities of (1.7–9.3)× 1022 cm−2. The bulk of the filaments are relatively cold (17–21 K), while some local clumps have a dust temperature up to 25–47 K. All the filaments are located within ≲60 pc from the Galactic mid-plane. Comparing the filaments to a recent spiral arm model incorporating the latest parallax measurements, we find that 7/9 of them reside within arms, but most are close to arm edges. These filaments are comparable in length to the Galactic scaleheight and therefore are not simply part of a grander turbulent cascade.

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