Formaldehyde observations of molecular clouds

Details Formaldehyde observations of molecular clouds Formaldehyde observations of molecular clouds

Sep 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986phdt.........7w&link_type=abstract

Ph.D. Thesis Virginia Univ., Charlottesville.

Astronomy and Astrophysics

Astronomy

2

Formaldehyde, Interstellar Gas, Molecular Clouds, Absorption Spectra, Emission Spectra, Gas Density, Molecular Energy Levels, Radio Astronomy, Radio Spectra

Scientific paper

The 1(11) to 1(10) and 2(12) to 2(11) K-doublet transitions H2CO have been observed in absorption towards 26 strong continuum radio sources in the first galactic quadrant. Ninety-seven discrete absorption components have been detected in the 6 cm 1(11) to 1(10) line. Of these, 69 have corresponding detections in the 2 cm 2(12) to 2(11) transition. The data were analyzed using a 16-level collisional excitation model and the collisional rate coefficients of Green et al. (1978), employing a spherically symmetric Large Velocity Gradient approximation to treat the radiative transfer. Median H2 densities of 9 x 10(4) cm(-3) were obtained for clouds near H II regions and 7 x 10(4) cm(-3) for clouds well removed from H II regions. Estimates of the ortho-H2CO column density, when combined with conservative estimates of the ortho-H2CO abundance, suggest that the H2CO traces a significant fraction (20 to 80%) of the total H2 column density seen in CO. No evidence is found in our data sample for the existence of a significant population of molecular clouds comprised solely of low density gas. Maps of the 6 cm and 2 cm H2CO absorption in the dense molecular core TMC-1 and high spatial resolution observations of the 2 cm H2CO emission in the rho Oph B cloud core are also presented.

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