H2CO MAPPING TOWARD DR21 AND W58 (K3=50)

We have mapped the distribution of 4.8-GHz H2CO absorption against the galactic Hn regions DR21 and W58 (K3#50) with 8arcsec resolution. Opacity variations on scales less than 18 arcsec (0.2 pc) are seen against the extended continuum emission toward DR21. Extreme variations are observed toward the various radio components in W58. The H2CO equivalent width is 5.2 km s1 in the direction of component CI; it is 2 column densities derived from the H2CO equivalent widths are compared to the visual extinction. Large variations in the apparent H2CO/H2 abundance ratio are derived for W58. © Royal Astronomical Society.