MagMar III -- Resisting the Pressure, Is the Magnetic Field Overwhelmed in NGC6334I?

TL;DR

This study uses ALMA observations to analyze magnetic fields, outflows, and turbulence in NGC6334I, revealing that magnetic energy is weaker than kinetic and outflow energies, and that protostellar feedback dominates turbulence injection.

Contribution

First detailed magnetic field strength measurements in NGC6334I combining polarization, Zeeman, and energy analysis, highlighting the magnetic field's limited role compared to feedback processes.

Findings

Magnetic field strengths range from 1 to 11 mG, averaging 1.9 mG.

Magnetic energy is weaker than outflow and feedback energies.

Gas conditions are mostly supersonic and trans-Alfvenic, moving towards super-Alfvenic.

Abstract

We report on ALMA observations of polarized dust emission at 1.2 mm from NGC6334I, a source known for its significant flux outbursts. Between five months, our data show no substantial change in total intensity and a modest 8\% variation in linear polarization, suggesting a phase of stability or the conclusion of the outburst. The magnetic field, inferred from this polarized emission, displays a predominantly radial pattern from North-West to South-East with intricate disturbances across major cores, hinting at spiral structures. Energy analysis of CS$(J=5 \rightarrow 4)$ emission yields an outflow energy of approximately $3.5\times10^{45}$ ergs, aligning with previous interferometric studies. Utilizing the Davis-Chandrasekhar-Fermi method, we determined magnetic field strengths ranging from 1 to 11 mG, averaging at 1.9 mG. This average increases to 4 $\pm 1$ mG when incorporating Zeeman measurements. Comparative analyses using gravitational, thermal, and kinetic energy maps reveal that magnetic energy is significantly weaker, possibly explaining the observed field morphology. We also find that the energy in the outflows and the expanding cometary {\HII} region is also larger than the magnetic energy, suggesting that protostellar feedback maybe the dominant driver behind the injection of turbulence in NGC6334I at the scales sampled by our data. The gas in NGC6334I predominantly exhibits supersonic and trans-Alfvenic conditions, transitioning towards a super-Alfvenic regime, underscoring a diminished influence of the magnetic field with increasing gas density. These observations are in agreement with prior polarization studies at 220 GHz, enriching our understanding of the dynamic processes in high-mass star-forming regions.