SCUBA Polarization Measurements of the Magnetic Field Strengths in the L183, L1544, and L43 Prestellar Cores

We have mapped linearly polarized dust emission from L183 with the JCMT SCUBA polarimeter and have analyzed these and our previously published data for the prestellar cores L183, L1544, and L43 in order to estimate magnetic field strengths in the plane of the sky, Bpos. The analysis used the ChandrasekharFermi technique, which relates the dispersion in polarization position angles to Bpos. We have used these estimates of the field strengths (neglecting the unmeasured line-of-sight component) to find the mass-to-magnetic flux ratios λ (in units of the critical ratio for magnetic support). Results are Bpos ≈ 80 μG and λ ≈ 2.6 for L183, Bpos ≈ 140 μG and λ ≈ 2.3 for L1544, and Bpos ≈ 160 μG and λ ≈ 1.9 for L43. Hence, for all three cores the mass-to-flux ratios are supercritical by a factor of ∼ 2, and magnetic support cannot prevent collapse. We note that for L183 and L1544 infall motions have been detected, suggesting collapse. These data are consistent with models of star formation driven by ambipolar diffusion in a weakly turbulent medium, but cannot rule out models of star formation driven by turbulence. Subject headings: ISM: magnetic fields — polarization ISM: individual: L183, L1544, L43 — stars: formation