Speaker
Ke Wang
(ESO)
Description
Co-authors:
Leonardo Testi(1), Adam Ginsburg(1), Malcolm Walmsley(2,3),Sergio Molinari(4), Eugenio Schisano(4)
1. ESO - European Southern Observatory, Garching bei München, Germany
2. INAF - Osservatorio astrofisico di Arcetri, Firenze, Italy
3. Dublin Institute of Advanced Studie, Dublin, Ireland
4. Istituto di Astrofisica e Planetologia Spaziali (IAPS) INAF, Roma, Italy
The ubiquity of filamentary structure at various scales through out 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 data complemented by spectral line cubes. We present a sample of the 9 most prominent Herschel filaments from a pilot search field. These filaments measure 37-99 pc long and 0.6-3.0 pc wide with masses (0.5-8.3)x10^4 Msun, and beam-averaged (28", or 0.4-0.7 pc) peak H_2 column densities of (1.7-9.3)x10^{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 due to local star formation activities. 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 scale height and therefore are not simply part of a grander turbulent cascade. These giant filaments, which often contain regularly spaced pc-scale clumps, are much larger than the filaments found in the Herschel Gould's Belt Survey, and they form the upper ends in the filamentary hierarchy. Full operational ALMA and NOEMA will be able to resolve and characterize similar filaments in nearby spiral galaxies, allowing us to compare the star formation in a uniform context of spiral arms.