Journal Article

Multiwavelength observations of cirrus clouds in the North Celestial Loop: physical parameters of molecular sites

L. Barriault, G. Joncas and R. Plume

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 2, pages 1250-1266
Published in print September 2011 | ISSN: 0035-8711
Published online September 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19121.x
Multiwavelength observations of cirrus clouds in the North Celestial Loop: physical parameters of molecular sites

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In this third paper of the series, we continue to investigate the transition between atomic and molecular gas in two potential sites of molecule formation at high Galactic latitude, which we call the Spider and Ursa Major. Using Five College Radio Astronomical Observatory 12CO (J= 1–0) observations and four clump identification algorithms, the clump properties are first determined in both regions, showing similar properties compared to the clumps found in translucent clouds. New higher resolution 12CO (J= 1–0) and 13CO (J= 1–0) observations from the Institut de Radioastronomie Millimétrique and new 12CO (J= 2–1) observations from the James Clerk Maxwell Telescope (resolution ≈20 arcsec) are also presented in five fields for the Spider (560 spectra) and in two fields for Ursa Major (288 spectra). Using a large velocity gradient model, physical parameters (density and column density) are determined in each field. The densities are smaller at the location of the infrared excess peaks (<200 cm−3) than at the locations of the 12CO peaks (≈103 cm−3), confirming that a small density could explain the absence of coincidence between the infrared excess peak and the 12CO peak. Self-shielding is probably efficient given the computed 12CO column densities (≈1015 cm−2).

Keywords: ISM: clouds; ISM: molecules; radio lines: ISM

Journal Article.  12752 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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