Probing the Rosette Nebula Stellar Bubble with Faraday Rotation

TL;DR

This study uses Faraday rotation measurements of background radio sources to analyze the plasma shell of the Rosette Nebula, providing insights into the nebula's magnetic environment and its interaction with the star cluster.

Contribution

It introduces detailed Faraday rotation measurements of the Rosette Nebula and compares simple plasma shell models to explain the observed magnetic field effects.

Findings

Excess rotation measure of 50-750 rad m^-2 observed through the nebula

Both plasma shell models can reproduce the rotation measure magnitude and extent

Stellar bubble model better explains the dependence of rotation measure on distance

Abstract

We report the results of Faraday rotation measurements of 23 background radio sources whose lines of sight pass through or close to the Rosette Nebula. The Rosette Nebula is an excellent candidate for studies of super bubbles associated with young star clusters. We made linear polarization measurements with the Karl G. Jansky Very Large Array (JVLA) at frequencies of 4.4GHz, 4.9GHz, and 7.7GHz. We are able to establish a background rotation measure in this part of the sky due to the Galaxy of +147 rad m^-2. Sources whose lines of sight pass through the nebula have an excess rotation measure of 50-750 rad m^-2, which we attribute to the plasma shell of the Rosette Nebula. We consider two simple plasma shell models and how they reproduce the magnitude and sign of the rotation measure, and its dependence on distance from the center of the nebula. These two models represent different modes of interaction of the Rosette Nebula star cluster with the surrounding interstellar medium. Both can reproduce the magnitude and spatial extent of the rotation measure enhancement, given plausible free parameters. We contend that the model based on a stellar bubble more closely reproduces the observed dependence of rotation measure on distance from the center of the nebula.