%0 Generic %1 citeulike:13665306 %A Li, Pak S. %A McKee, Christopher F. %A Klein, Richard I. %D 2015 %K imported %T Magnetized Interstellar Molecular Clouds. I. Comparison Between Simulations and Zeeman Observations %U http://arxiv.org/abs/1506.08228 %X The most accurate measurements of magnetic fields in star-forming gas are based on the Zeeman observations analyzed by Crutcher et al. (2010). We show that their finding that the 3D magnetic field scales approximately as density\$^0.65\$ can also be obtained from analysis of the observed line-of-sight fields. We present two large-scale AMR MHD simulations of several thousand \$M\_ødot\$ of turbulent, isothermal, self-gravitating gas, one with a strong initial magnetic field (Alfven Mach number \$M\_A,0= 1\$) and one with a weak initial field (\$M\_A,0=10\$). We construct samples of the 100 most massive clumps in each simulation and show that they exhibit a power-law relation between field strength and density in excellent agreement with the observed one. Our results imply that the average field in molecular clumps in the interstellar medium is \$<B\_tot> 42 n\_H,4^0.65 \mu\$G. Furthermore, the median value of the ratio of the line-of-sight field to density\$^0.65\$ in the simulations is within a factor of about (1.3, 1.7) of the observed value for the strong and weak field cases, respectively. The median value of the mass-to-flux ratio, normalized to the critical value, is 70\% of the line-of-sight value. This is larger than the 50\% usually cited for spherical clouds because the actual mass-to-flux ratio depends on the volume-weighted field, whereas the observed one depends on the mass-weighted field. Our results indicate that the typical molecular clump in the ISM is significantly supercritical (\~ factor of 3). The results of our strong-field model are in very good quantitative agreement with the observations of Li et al. (2009), which show a strong correlation in field orientation between small and large scales. Because there is a negligible correlation in the weak-field model, we conclude that molecular clouds form from strongly magnetized (although magnetically supercritical) gas.

@misc{citeulike:13665306, abstract = {The most accurate measurements of magnetic fields in star-forming gas are based on the Zeeman observations analyzed by Crutcher et al. (2010). We show that their finding that the 3D magnetic field scales approximately as density\$^{0.65}\$ can also be obtained from analysis of the observed line-of-sight fields. We present two large-scale AMR MHD simulations of several thousand \$M\_\odot\$ of turbulent, isothermal, self-gravitating gas, one with a strong initial magnetic field (Alfven Mach number \$M\_{A,0}= 1\$) and one with a weak initial field (\$M\_{A,0}=10\$). We construct samples of the 100 most massive clumps in each simulation and show that they exhibit a power-law relation between field strength and density in excellent agreement with the observed one. Our results imply that the average field in molecular clumps in the interstellar medium is \$\<B\_{tot}\> \sim 42 n\_{H,4}^{0.65} \mu\$G. Furthermore, the median value of the ratio of the line-of-sight field to density\$^{0.65}\$ in the simulations is within a factor of about (1.3, 1.7) of the observed value for the strong and weak field cases, respectively. The median value of the mass-to-flux ratio, normalized to the critical value, is 70\% of the line-of-sight value. This is larger than the 50\% usually cited for spherical clouds because the actual mass-to-flux ratio depends on the volume-weighted field, whereas the observed one depends on the mass-weighted field. Our results indicate that the typical molecular clump in the ISM is significantly supercritical (\~{} factor of 3). The results of our strong-field model are in very good quantitative agreement with the observations of Li et al. (2009), which show a strong correlation in field orientation between small and large scales. Because there is a negligible correlation in the weak-field model, we conclude that molecular clouds form from strongly magnetized (although magnetically supercritical) gas.}, added-at = {2019-03-25T08:20:55.000+0100}, archiveprefix = {arXiv}, author = {Li, Pak S. and McKee, Christopher F. and Klein, Richard I.}, biburl = {https://www.bibsonomy.org/bibtex/2a8362b62e377aed995cf249f7573c540/ericblackman}, citeulike-article-id = {13665306}, citeulike-linkout-0 = {http://arxiv.org/abs/1506.08228}, citeulike-linkout-1 = {http://arxiv.org/pdf/1506.08228}, day = 26, eprint = {1506.08228}, interhash = {97726115734c7be4bfe9f17280f2fb87}, intrahash = {a8362b62e377aed995cf249f7573c540}, keywords = {imported}, month = jun, posted-at = {2015-07-06 05:18:07}, priority = {2}, timestamp = {2019-03-25T08:20:55.000+0100}, title = {{Magnetized Interstellar Molecular Clouds. I. Comparison Between Simulations and Zeeman Observations}}, url = {http://arxiv.org/abs/1506.08228}, year = 2015 }