An observational correlation between magnetic field, angular momentum and fragmentation in the envelopes of Class 0 protostars?

Abstract

Aims. The main goal of the following analysis is to assess the potential role of magnetic fields in regulating the envelope rotation, the formation of disks and the fragmentation of Class 0 protostars in multiple systems. Methods. We use the Submillimeter Array to carry out observations of the dust polarized emission at 0.87 mm, in the envelopes of a large sample of 20 Class 0 protostars. We estimate the mean magnetic field orientation over the central 1000 au envelope scales to characterize the orientation of the main component of the organized magnetic field at the envelope scales in these embedded protostars. This direction is compared to that of the protostellar outflow in order to study the relation between their misalignment and the kinematics of the circumstellar gas. The latter is traced via velocity gradient observed in the molecular line emission (mainly N2H+) of the gas at intermediate envelope scales. Results. We discover a strong relationship between the misalignment of the magnetic field orientation with the outflow and the amount of angular momentum observed at similar scales in the protostellar envelope, revealing a potential link between the kinetic and the magnetic energy at envelope scales. The relation could be driven by favored B-misalignments in more dynamical envelopes or a dependence of the envelope dynamics with the large-scale B initial configuration. Comparing the trend with the presence of fragmentation, we observe that single sources are mostly associated with conditions of low angular momentum in the inner envelope and good alignment of the magnetic field with protostellar outflows, at intermediate scales. Our results suggest that the properties of the magnetic field in protostellar envelopes bear a tight relationship with the rotating-infalling gas directly involved in the star and disk formation: we find that it may not only influence the fragmentation of protostellar cores into multiple stellar systems, but also set the conditions establishing the pristine properties of planet-forming disks.

Magnetic fields in star formation: from clouds to cores

“…Interferometric studies of core-scale magnetic field and outflow orientation have suggested that alignment is typically random, with a possible highly-correlated subset (Hull et al 2014;Zhang et al 2014;Hull and Zhang 2019), while observations of protostellar envelopes find fields to be preferentially either parallel or perpendicular to the outflow, with misalignment more common in sources with larger rotational energies (Galametz et al 2018(Galametz et al , 2020. A comparable single-dish study found that outflows and local magnetic fields tend to be misaligned by 50 • ± 15 • in 3D, but did not rule out random orientation (Yen et al 2021).…”

Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration

“…Current observations with single dish instruments (such as Planck, BLASTPOL and the JCMT POL2), as well as interferometric facilities (such as ALMA, CARMA and SMA) are providing a wealth of polarimetric data that, if properly interpreted, can deepen our insight on the different processes occurring in different environments. For instance, recent interferometric observations with the SMA have allowed Galametz et al (2020) to highlight the potentially crucial role of the relative orientation between the magnetic field orientation, inferred from the polarized dust emission, and the rotation axis, inferred from the direction of the outflows and jets, on the fragmentation and multiplicity properties of protostars. Even though the ability of the polarized signal arising from aligned dust grains to trace the orientation of the magnetic fields is well established for the interstellar gas, it is still necessary to assess its robustness as a tracer of the magnetic field topology in the case of objects displaying a higher degree of complexity such as young protostars, since important conclusions are drawn from polarimetric observations, such as in the previously cited work.…”

What Produces Dust Polarization in the HH 212 Protostellar Disk at 878 μm: Dust Self-Scattering or Dichroic Extinction?

“…Note that the disk axis has a position angle of ∼ 23 • , well aligned with the jet axis (Lee et al 2017a). In the flattened envelope at a size scale of ∼ 1500 au, the magnetic fields are found to have a similar mean axis to that in the molecular core (Galametz et al 2020). Interestingly, the innermost flattened envelope with a size scale of ∼ 500 au detected in dust continuum also has an axis with a similar position angle of ∼ 36 • ±10 • (see Figure 1c Lee et al 2017a).…”

“…Recently, dust polarization due to aligned grains has also been detected on the larger scales in the dense molecular core and the flattened envelope around the disk, revealing magnetic field morphology there (Yen et al 2021;Galametz et al 2020), and thus allowing us to check the possible presence of poloidal fields in the outer disk. In the molecular core at a size scale of ∼ 0.1 pc, the magnetic fields are found to be poloidal with a mean axis at a position angle of ∼ 35 • ±10 • , slightly misaligned with the disk axis (of symmetry) by ∼ 12 • counterclockwise (see Figure 11 in Yen et al 2021).…”