H I Self-Absorption and the Kinematic Distance Ambiguity: The Case of the Molecular Cloud GRSMC 45.6+0.3

Details H I Self-Absorption and the Kinematic Distance Ambiguity: The Case of the Molecular Cloud GRSMC 45.6+0.3 H I Self-Absorption and the Kinematic Distance Ambiguity: The Case of the Molecular Cloud GRSMC 45.6+0.3

Feb 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...566l..81j&link_type=abstract

The Astrophysical Journal, Volume 566, Issue 2, pp. L81-L84.

Astronomy and Astrophysics

Astronomy

37

Galaxy: Kinematics And Dynamics, Galaxy: Structure, Ism: Atoms, Ism: Clouds, Ism: Molecules

Scientific paper

We report on a three-dimensional (l, b, VLSR) physical association of H I self-absorption with 13CO emission toward the Galactic molecular cloud GRSMC 45.6+0.3. Photochemical models indicate that a significant column density of cool (T<~25 K) H I exists in the skins (Av<~2) of typical Galactic molecular clouds. The H I self-absorption can thus be produced by the cool cloud skin absorbing the warm (TSPIN~100 K) background H I emission that is ubiquitously distributed throughout the Galaxy. Liszt, Burton, and Bania have suggested that because cool H I in a molecular cloud will absorb warmer H I background line emission, H I self-absorption can be used to resolve the kinematic distance ambiguity for molecular clouds in the inner Galaxy. Clouds at the near distance should show H I self-absorption, whereas clouds at the far distance will not since there is no background to absorb. The near kinematic distance of 1.8 kpc for the GRSMC 45.6+0.3 molecular cloud is independently confirmed by its morphological correlation with foreground optical extinction.

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