Outflows, cores, and magnetic field orientations in W43-MM1 as seen by ALMA

C Arce-Tord,F Louvet,L Bronfman,P Didelon,G Garay,V J M Le Gouellec,P C Cortes,T Nony,F Motte,C L H Hull

doi:10.1051/0004-6361/202038024

Abstract

Aims. It has been proposed that the magnetic field, which is pervasive in the interstellar medium, plays an important role in the process of massive star formation. To better understand the impact of the magnetic field at the pre- and protostellar stages, high-angular resolution observations of polarized dust emission toward a large sample of massive dense cores are needed. We aim to reveal any correlation between the magnetic field orientation and the orientation of the cores and outflows in a sample of protostellar dense cores in the W43-MM1 high-mass star-forming region. Methods. We used the Atacama Large Millimeter Array in Band 6 (1.3 mm) in full polarization mode to map the polarized emission from dust grains at a physical scale of ~2700 au. We used these data to measure the orientation of the magnetic field at the core scale. Then, we examined the relative orientations of the core-scale magnetic field, of the protostellar outflows, and of the major axis of the dense cores determined from a 2D Gaussian fit in the continuum emission. Results. We find that the orientation of the dense cores is not random with respect to the magnetic field. Instead, the dense cores are compatible with being oriented 20–50° with respect to the magnetic field. As for the outflows, they could be oriented 50–70° with respect to the magnetic field, or randomly oriented with respect to the magnetic field, which is similar to current results in low-mass star-forming regions. Conclusions. The observed alignment of the position angle of the cores with respect to the magnetic field lines shows that the magnetic field is well coupled with the dense material; however, the 20–50° preferential orientation contradicts the predictions of the magnetically-controlled core-collapse models. The potential correlation of the outflow directions with respect to the magnetic field suggests that, in some cases, the magnetic field is strong enough to control the angular momentum distribution from the core scale down to the inner part of the circumstellar disks where outflows are triggered.

Highlights

It has been proposed that the magnetic field, which is pervasive in the interstellar medium (ISM), might play an important role in the dynamical evolution of star-forming clouds
The very few existing observational studies, which have reported this type of behavior, had very limited samples: Davidson et al (2011) studied 350 μm polarization observations taken at the CSO toward three low-mass Class 0 protostars, and they report a magnetic field orientation, in loose agreement with the magnetically-controlled core-collapse predictions; Chapman et al (2013) found the magnetic field orientation to be perpendicular to the pseudodisks in four low-mass cores, using 350 μm polarization observations taken at the CSO; Qiu et al (2014) report a similar result
In this work, which is based on a sample of 28 outflow lobes, we find two configurations to be compatible with the observational cumulative distribution functions (CDFs) of the angle difference between the orientation of the outflows and the magnetic field orientation

Summary

Introduction

It has been proposed that the magnetic field, which is pervasive in the interstellar medium (ISM), might play an important role in the dynamical evolution of star-forming clouds (e.g., Shu et al 1987; Hennebelle et al 2011; Commerçon et al 2011; Crutcher 2012; Planck Collaboration Int. XXXV 2016; Planck Collaboration Int. XXXIII 2016; Matsushita et al 2018; Beuther et al 2018). Large-scale observations (∼1 pc) of the magnetic field revealed a well-ordered structure in the lowdensity envelopes of molecular clouds, suggesting that parsecscale envelopes are magnetically supported against gravitational collapse (e.g., Franco et al 2010).

Results

Discussion

Conclusion