Portal de Periódicos da CAPES

THE IMPORTANCE OF THE MAGNETIC FIELD FROM AN SMA-CSO-COMBINED SAMPLE OF STAR-FORMING REGIONS

2014; IOP Publishing; Volume: 797; Issue: 2 Linguagem: Inglês

10.1088/0004-637x/797/2/99

1538-4357

Patrick M. Koch, Ya‐Wen Tang, Paul T. P. Ho, Qizhou Zhang, J. M. Girart, Huei-Ru Vivien Chen, P. Frau, Hua-Bai Li, Zhi-Yun Li, Hauyu Baobab Liu, M. Padovani, Keping Qiu, Hsi-Wei Yen, Hope How-Huan Chen, Tao-Chung Ching, S. Lai, Ramprasad Rao,

Astro and Planetary Science

Submillimeter dust polarization measurements of a sample of 50 star-forming regions, observed with the SMA and the CSO covering pc-scale clouds to mpc-scale cores, are analyzed in order to quantify the magnetic field importance. The magnetic field misalignment $\delta$ -- the local angle between magnetic field and dust emission gradient -- is found to be a prime observable, revealing distinct distributions for sources where the magnetic field is preferentially aligned with or perpendicular to the source minor axis. Source-averaged misalignment angles $\langle|\delta|\rangle$ fall into systematically different ranges, reflecting the different source-magnetic field configurations. Possible bimodal $\langle|\delta|\rangle$-distributions are found for the separate SMA and CSO samples. Combining both samples broadens the distribution with a wide maximum peak at small $\langle|\delta|\rangle$-values. Assuming the 50 sources to be representative, the prevailing source-magnetic field configuration is one that statistically prefers small magnetic field misalignments $|\delta|$. When interpreting $|\delta|$ together with an MHD force equation, as developed in the framework of the polarization-intensity gradient method, a sample-based scaling fits the magnetic field tension-to-gravity force ratio $\langle\Sigma_B\rangle$ versus $\langle|\delta|\rangle$ with $\langle\Sigma_B\rangle = 0.116 \cdot \exp(0.047\cdot \langle|\delta|\rangle)\pm 0.20$ (mean error), providing a way to estimate the relative importance of the magnetic field, only based on measurable field misalignments $|\delta|$. The force ratio $\Sigma_B$ discriminates systems that are collapsible on average ($\langle \Sigma_B\rangle 1$) (abridged).