RESOLVED MAGNETIC FIELD MAPPING OF A MOLECULAR CLOUD USING GPIPS.

We present the first resolved map of plane-of-sky magnetic field strength for a quiescent molecular cloud. GRSMC 45.60+0.30 subtends 40 × 10 pc at a distance of 1.88 kpc, masses 16,000 M_☼, and exhibits no star formation. Near-infrared background starlight polarizations were obtained for the Galactic Plane Infrared Polarization Survey using the 1.8 m Perkins telescope and the Mimir instrument. The cloud area of 0.78 deg² contains 2684 significant starlight polarizations for Two Micron All Sky Survey matched stars brighter than 12.5 mag in the H band. Polarizations are generally aligned with the cloud's major axis, showing an average position angle dispersion of 15 ± 2° and polarization of 1.8 ± 0.6%. The polarizations were combined with Galactic Ring Survey ¹³CO spectroscopy and the Chandrasekhar-Fermi method to estimate plane-of-sky magnetic field strengths, with an angular resolution of 100 arcsec. The average plane-of-sky magnetic field strength across the cloud is 5.40 ± 0.04 μG. The magnetic field strength map exhibits seven enhancements or “magnetic cores.” These cores show an average magnetic field strength of 8.3 ± 0.9 μG, radius of 1.2 ± 0.2 pc, intercore spacing of 5.7 ± 0.9 pc, and exclusively subcritical mass-to-flux ratios, implying their magnetic fields continue to suppress star formation. The magnetic field strength shows a power-law dependence on gas volume density, with slope 0.75 ± 0.02 for ⩾10 cm^–3. This power-law index is identical to those in studies at higher densities, but disagrees with predictions for the densities probed here. [ABSTRACT FROM AUTHOR]