2001A&A...371..274U

We present measurements of Zeeman splitting in SO J_N=1₂-1₁ line emission/absorption arising from dense thermal gas (>10⁶cm^–3) associated with ten compact HII and star-forming regions. No line-of-sight magnetic field, above an average 1σ limit of 0.57mG, is detected toward any of these sources. The W3(OH) region, found in a previous study to have a line-of-sight field of 3mG in its dense gas, is thus unique in this respect. The implication of this study is that the magnetic fields in dense clouds are supercritical in the sense that they are not capable of supporting their host clouds against gravitational collapse. The relatively low average field limit is consistent with those theories predicting the quick onset of and short timescales for ambipolar diffusion. Also presented are (1) Zeeman splitting measurements of the CCS J_N=1₀-0₁ line probing the 10^4–5cm^–3 gas towards three positions in the Taurus star forming region, giving a 1σ average upper limit of 66µG, and (2) measurements of Zeeman splitting in the OH ²Π_3/2J=7/2F=3⁺-3^– hyperfine line toward the compact HII regions DR-21 and G10.62.