Oral Presentation

Magnetic Field in Massive Protoclusters

Author(s): Vivien Chen (NTHU); Qizhou Zhang (CfA)

Presenter: Vivien Chen (National Tsing Hua University)

The influence of magnetic fields on dynamics and timescales of star formation remains an open question. The alignment of magnetic field with respect to mass accretion flow renders greatly different expectation for gas kinematics. Polarized emission arising from magnetically aligned dust grains in the mm/sub-mm wavebands is often used to map the 2D morphology of the 3D magnetic fields on the plane of sky. Although a pinched field morphology aligned with the outflow axis has been reported in a few massive porto-clusters, it remains unclear whether these cases well represent the rich diversity of forming clusters. As part of the SMA polarization legacy project, we have observed the polarized dust emission at 882um in the nearby (1.83 kpc) massive protocluster W3 IRS5 with an angular resolution of 2.7” (~5000 AU). W3 IRS 5 is a luminous proto-cluster with at least eight hyper-compact HII regions and makes a much younger analogue to the Trapezium system. Our polarization maps show a pinched morphology while the CO emission suggests two pairs of bipolar outflows. We have developed radiative transfer models to interpret the observed polarized dust emission. We are able to reproduce observed polarization pattern with a misaligned hourglass geometry of magnetic field. This suggests that the magnetic field does not necessarily remain well-aligned at scales of cluster formation. Comparison with the case of G240.31+0.07, which displays a well-aligned field morphology, will also be discussed.