Magnetic Fields Under Feedback: A Case Study of the Massive Star-Forming Hub G34.26+0.15

TL;DR

This study uses polarized submillimeter observations to analyze magnetic field structures in a high-mass star-forming cloud, revealing feedback effects from an HII region and estimating magnetic field strength.

Contribution

It introduces the filament and ellipse alignment factors to assess magnetic field orientation relative to structures, highlighting feedback effects on magnetic fields in star formation.

Findings

Magnetic field generally aligns with filaments in the northwest.

HII region expansion radically reshapes the magnetic field.

Magnetic field strength estimated at 0.5-1.4 mG.

Abstract

We present 850$\mu$m polarized observations of the molecular cloud G34.26+0.15 taken using the POL-2 polarimeter mounted on the James Clerk Maxwell Telescope (JCMT). G34.26+0.15 is a hub-filament system with ongoing high-mass star-formation, containing multiple HII regions. We extend the Histogram of Relative Orientations technique with an alternative application that considers the alignment of the magnetic field to the filaments and a HII region boundary, denoted as the filament alignment factor ($\xi_{F}$) and the ellipse alignment factor ($\xi_{E}$) respectively. Using these metrics, we find that, although in general the magnetic field aligns parallel to the filamentary structure within the system in the north-west, the magnetic field structure of G34.26+0.15 has been radically reshaped by the expansion of an evolved HII region in the south-east, which itself may have triggered further high-mass star formation in the cloud. Thus, we suggest high-mass star formation is both occurring through mass accretion as per the hub-filament model from one side, and through compression of gas under stellar feedback from the other. We also use HARP observations of C$^{18}$O from the CHIMPS survey to estimate the magnetic field strength across the cloud, finding strengths of $\sim$0.5-1.4 mG.