Tuesday 6/18/13

Not too much today, but a study of CO-to-H2 in a diffuse molecular cloud within the Milky Way, which is maybe interesting for some!

Title: A High-Resolution Study of the CO-H2 Conversion Factor in the Diffuse Cloud MBM 40
Authors: Cotten, David L.; Magnani, Loris
Publication: eprint arXiv:1306.3972
Publication Date: 06/2013
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics
Comment: 27 pages, 2 figures
Bibliographic Code: 2013arXiv1306.3972C


We made CO(1-0) observations of 103 lines of sight in the core and envelope of the high-latitude cloud MBM 40 to determine how the CO-H_2 conversion factor (X_CO) varies throughout the cloud. Calibrating X_CO with CH data at similar resolution (1′ for CO, 1.5′ for CH) yields values of X_CO ranging from 0.3 10^20 to 3.6 10^20 cm^-2 [K km s^-1]^-1 with an average of 1.5 +/- 0.3 10^20 cm^-2 [K km s^-1]^-1. Given that the cloud has a peak reddening of 0.24 mag, it should be classed as a diffuse rather than a translucent molecular cloud. The mass obtained from the CO data and our values of X_CO is 9.6 M(solar) for the core, 12 M(solar) for the envelope, and 10 M(solar) for the periphery of the cloud. A third of the molecular mass of the cloud is found in a region with E(B-V) < 0.12 mag. With these mass estimates, we determine that the cloud is not gravitationally bound.

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