Magnetic fields in massive star-forming regions (MagMaR)

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Abstract
Context . Accretion streamers connected to protostellar disks and/or envelopes are thought to transport material across several thousand of au. Whether the motions of the gas comprising these streamers are dominated by gravity, large scale external turbulence or the action of magnetic fields is still under scrutiny. Aims . The aim of this work is to understand the role of the magnetic fields in the star-formation processes, in particular the role that magnetic forces have in potentially leading flows of gas and accretion onto the envelopes and disks orbiting protostars. Methods . First, we try to identify large-scale accretion streamers toward the high-mass Young Stellar Object GGD 27–MM1 and fit their trajectories using the so-called Mendoza model, a modification of the classical model of pure gravitational infalling motion of fluid particles in a potential well. Second, we estimate the strength of the magnetic field associated with the streamers. Then, we determine whether the streamers are dominated by magnetic or centrifugal forces. Results . Inspecting the Atacama Large Millimeter/submillimeter Array (ALMA) H 2 CO cube we were able to identify four accretion streamers spreading up to ∼7000 au and fit their trajectories in the position-position-velocity space. The polarized continuum emission reveals a good alignment of the magnetic field and the trajectory of the streamers. Using the Davis-Chandrasekhar-Fermi (DCF) method, we derive estimates for the magnetic field strength, find that the streamers are sub-Alfvénic, and discuss (after estimating energy terms for turbulence, ordered motions, magnetic forces, and gravity) a possible qualitative scenario in which, the gravitational well of the GGD 27–MM1 protostar dominates streamer gas motions over turbulence and magnetic forces at distances of ∼3000 au.

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