MM SUBMM-BOLOMETER OBSERVATIONS OF STAR-FORMING REGIONS

Methods are described to estimate hydrogen column densities and masses using molecular lines and mm/submm dust emission as probes (Section I ). Possible errors and uncertainties in the latter method are discusse d (Section II). NGC2024 is shown as an example where molecular lines c ease to be reliable tracers of hydrogen column densities (Section III) . Sgr B2 is shown as an example where FIR dust emission observed by IR AS misses a dense and cool GMC because its interior dust is too cool ( Section IV).