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arXiv · 1510.06784

A Global View of Molecule-Forming Clouds in the Galaxy

Steven J. Gibson·Ward S. Howard·Christian S. Jolly·Jonathan H. Newton·Aaron C. Bell·Mary E. Spraggs·J. Marcus Hughes·Aaron M. Tagliaboschi·Christopher M. Brunt·A. Russell Taylor·Jeroen M. Stil·Thomas M. Dame
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Abstract

We have mapped cold atomic gas in 21cm line HI self-absorption (HISA) at arcminute resolution over more than 90% of the Milky Way's disk. To probe the formation of H2 clouds, we have compared our HISA distribution with CO J=1-0 line emission. Few HISA features in the outer Galaxy have CO at the same position and velocity, while most inner-Galaxy HISA has overlapping CO. But many apparent inner-Galaxy HISA-CO associations can be explained as chance superpositions, so most inner-Galaxy HISA may also be CO-free. Since standard equilibrium cloud models cannot explain the very cold HI in many HISA features without molecules being present, these clouds may instead have significant CO-dark H2.

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Steven J. Gibson, Ward S. Howard, Christian S. Jolly, Jonathan H. Newton, Aaron C. Bell, Mary E. Spraggs, J. Marcus Hughes, Aaron M. Tagliaboschi, Christopher M. Brunt, A. Russell Taylor, Jeroen M. Stil, Thomas M. Dame. 2015-10-22. A Global View of Molecule-Forming Clouds in the Galaxy. https://doi.org/10.1017/s1743921316007882

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