# A Curved Magnetic field in the ring-like shell of bubble N4

## TL;DR

This study detects a curved magnetic field in the shell of bubble N4, showing magnetic field strengthening due to compression, which may influence star formation processes in the region.

## Contribution

It provides the first measurement of a curved magnetic field in the shell of bubble N4 using near-infrared polarization data.

## Key findings

- Magnetic field strength in the shell is about 120 μG.
- The shell's magnetic field is parallel and curved along the ring.
- All submillimeter clumps are magnetically subcritical.

## Abstract

We report the detection of a curved magnetic field in the ring-like shell of the bubble N4, derived from near-infrared polarization of reddened diskless stars located behind this bubble. The magnetic field in the shell is curved and parallel to the ring-like shell, and its strength is estimated to be $\sim120\,\mu$G in the plane of the sky. The magnetic field strength in the shell is significantly enhanced compared to the local field strength. We calculate the mass-to-flux ratio for the submillimeter clumps in the shell and find that they are all magnetically subcritical. Our results demonstrate that the magnetic field strengthens as the interstellar medium is compressed into a shell, and suggest that the magnetic field has the potential to hinder star formation triggered by \ion{H}{2} region expansion.