Publication Date:
2015-05-29
Description:
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) 10 4 M , and beam-averaged (28 arcsec, or 0.4–0.7 pc) peak H 2 column densities of (1.7–9.3) x 10 22 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.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
