ON THE QUESTION OF DARK-MATTER AND COLD H-2

Lequeux et al. (1993) have proposed that there is a substantial amount of mass in cold H-2 clouds in the outer galaxy. We test this hypothes is using recent molecular line observations toward the supernova remna nt Cassiopeia A. From H2CO and OH absorption and CO emission line data , the molecular clouds toward Cas A are not interacting with this supe rnova remnant, so are typical interstellar clouds with A(v) approximat ely 3m. These clouds are in the Perseus spiral arm, approximately 10 k pc from the galactic center, that is, in the outer galaxy. Since these clouds have been selected on the basis of absorption line surveys, th ere is no bias toward warm molecular gas as in CO emission line survey s. Comparisons with 20'' resolution emission line maps of CO are used to determine the kinetic temperature, T(k). The region sampled is appr oximately 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 T(k) as low as 6 K. Cold H-2 makes u p a mass fraction of <3%.