On the question of dark matter and cold H2

Details On the question of dark matter and cold H2 On the question of dark matter and cold H2

Feb 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...282l..41w&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 282, no. 3, p. L41-L44

Astronomy and Astrophysics

Astrophysics

14

Absorption Spectra, Dark Matter, Hydrogen Clouds, Interstellar Matter, Line Spectra, Molecular Clouds, Molecular Spectra, Supernova Remnants, Astronomical Spectroscopy, Carbon Monoxide, Formaldehyde, Hydroxyl Radicals

Scientific paper

Lequeux et al. (1993) have proposed that there is a substantial amount of mass in cold H2 clouds in the outer galaxy. We test this hypothesis using recent molecular line observations toward the supernova remnant Cassiopeia A. From H2CO and OH absorption and CO emission line data, the molecular clouds toward Cas A are not interacting with this supernova remnant, so are typical interstellar clouds with Av. These are clouds are in the Perseus spiral arm, approximately 10 kpc from the galactic center, that is, in the outer galaxy. Since these clouds have selected on the basis of absorption line surveys, there is no bias toward warm molecular gas as in CO emission line surveys. Comparisons with 20 resolution emission line surveys. Comparisons with 20 sec resolution emission line maps of CO are used to determine the kinetic temperature, Tk. The region sampled is approximately 16 square arcmin, much more than can ever be observed using line absorption spectra toward extragalactic sources. Of more than 15 clouds toward Cas A, only one has Tk as low as 6 K. Cold H2 makes up a mass fraction of less than 8%.

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