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H. G. Arce (AMNH), GALFA ``HI and Molecular Clouds" Subconsortium
Observations of the neutral hydrogen (HI) gas around and inside molecular clouds can provide important insight on the formation, evolution and physical conditions of molecular clouds. The first step in studying how molecular clouds are formed from low-density HI clouds is to observe and study the distribution and kinematics of the neutral gas near molecular clouds and compare it with the distribution and kinematics of the molecular gas. The powerful mapping capabilities of the Arecibo L-band Feed Array (ALFA) will allow us to produce large-scale maps of the HI emission surrounding different molecular clouds. The proposed ALFA observations, in concert with large-scale high-resolution molecular line maps of the same regions, will provide an unprecedented data set from which a detailed comparison between the HI and the molecular gas in different molecular cloud environments could be produced. Such a detailed comparison is needed to discriminate among existing models of molecular cloud formation.
In addition, the proposed Galactic ALFA HI observations will allow us to map and study the distribution and kinematics of the cold HI (traced by narrow absorption lines) associated with dense cold regions in molecular clouds. The cold HI data are essential in order to estimate the neutral hydrogen fractional abundance, an important parameter for modeling the chemical evolution of the molecular clouds both from the point of view of determining their ''age," and the possible effects of dynamic processes such as turbulent diffusion.
Preliminary results from the ALFA test observations of the Taurus molecular cloud region are shown.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.