A young stellar cluster within the RCW41 HII region: deep NIR photometry and Optical/NIR polarimetry

TL;DR

This study investigates the magnetic fields and young stellar population in the RCW41 star-forming region using optical/NIR polarimetry and deep photometry, revealing insights into star formation processes and magnetic field behavior.

Contribution

It provides the first detailed analysis of interstellar polarization and magnetic field structure in RCW41, along with characterization of its young stellar cluster and evidence of sequential star formation.

Findings

Magnetic field lines are distorted, following the region's borders and pointing radially inward.

A cluster age of 2.5-5 million years was estimated, indicating recent star formation.

Polarization degree decreases in the ionized core, suggesting turbulence and weak magnetic fields.

Abstract

The RCW41 star-forming region is embedded within the Vela Molecular Ridge, hosting a massive stellar cluster surrounded by a conspicuous HII region. Understanding the role of interstellar magnetic fields and studying the newborn stellar population is crucial to build a consistent picture of the physical processes acting on this kind of environment. We have carried out a detailed study of the interstellar polarization toward RCW41, with data from an optical and near-infrared polarimetric survey. Additionally, deep near-infrared images from the NTT 3.5m telescope have been used to study the photometric properties of the embedded young stellar cluster, revealing several YSO's candidates. By using a set of pre-main sequence isochrones, a mean cluster age in the range 2.5 - 5.0 million years was determined, and evidence of sequential star formation were revealed. An abrupt decrease in R-band polarization degree is noticed toward the central ionized area, probably due to low grain alignment efficiency caused by the turbulent environment and/or weak intensity of magnetic fields. The distortion of magnetic field lines exhibit a dual behavior, with the mean orientation outside the area approximately following the borders of the star-forming region, and directed radially toward the cluster inside the ionized area, in agreement with simulations of expanding HII regions. The spectral dependence of polarization allowed a meaningful determination of the total-to-selective extinction ratio by fittings of the Serkowski relation. Furthermore, a large rotation of polarization angle as a function of wavelength is detected toward several embedded stars.