Evolution of magnetized hub-filament systems: Comparing the observed properties of W3(OH), W3 Main, and S 106

TL;DR

This study investigates the magnetic field structures and filament properties of three evolving hub-filament systems, revealing how magnetic alignment, filament mass, and star formation indicators change during evolution, with implications for understanding cluster formation.

Contribution

It provides new JCMT/POL-2 polarization observations and analysis of magnetic fields, filament line-masses, and star formation indicators across different evolutionary stages of HFS.

Findings

Filament line-mass functions evolve with HFS stage.

Magnetic field alignment with filaments changes during evolution.

Hub sizes correlate with young cluster radii and show 'double-node' star formation features.

Abstract

In this study, we examine three cluster-forming hub-filament systems (HFS) - W3(OH), W3 Main, and S 106 - spanning evolutionary stages from early to advanced, with a focus on their magnetic field (B-field) structures and filament line-mass distributions. Our goal is to identify indicators of HFS evolution, particularly within their hubs, as star formation progresses. Our analysis combines observations of dense star-forming gas and young stellar populations. We present new JCMT/POL-2 observations of 850micron dust polarized emission to probe magnetic field morphology and dense gas structures. Archival infrared and radio data are also used to trace star formation activity. We derive radial column density profiles centered on the hubs to define distinct filament and hub regions. We then analyze histograms of line mass, polarization intensity (PI), polarization fraction (PF), and the relative orientation between B-fields and filaments. As HFS evolve, we observe changes in the filament line-mass function (FLMF), PF, and B-field-filament alignment - especially within the hub, which also increases in size. Massive bipolar outflows and radiation bubbles reshape the plane-of-sky B-fields, aligning them with cavity walls and shells, consistent with known rearrangements near HII regions. We also find a notable similarity between hub sizes and young cluster radii. "Double-node" star formation - where two subregions within a hub show different evolutionary stages - emerges as a common HFS feature. We present evidence for its widespread occurrence across several well-studied, nearby star-forming clouds.