Star formation, polarization, and magnetic fields in the ALMA era (Dr. Chat Hull; NAOJ, JAO Chile)

From October 01, 2019 15:15 until October 01, 2019 16:30

Categories: Coloquios

New ALMA polarization observations continue to both expand and confound our understanding of the role played by the magnetic field in low-mass star formation. The sample of very young, Class 0 protostellar sources observed with high resolution and high sensitivity with ALMA is now large enough that we are beginning to see the same surprising features in multiple sources. The first of these are magnetic field morphologies that beautifully trace the outflow cavity walls in several objects, indicating that the outflow has shaped the magnetic field. The polarization along the cavities is strongly enhanced, and in some cases is co-located with emission from UV-tracing molecules, suggesting that the origin of the enhanced polarization is the strong irradiation of the outflow cavities. The second, more puzzling set of features are thin structures with well organized magnetic fields that are not associated with outflow cavity walls, and yet have high polarization fractions in spite of being deeply embedded and far from any obvious source of the photons necessary to align the grains. I will close by discussing recent observations of polarization toward much more evolved, Class II protoplanetary disks.  In the case of my work on IM Lup (one of these disks): consistent with some observations of other disks, the polarization at Bands 6 and 7 (1.3 mm and 850 microns) appears to be due to scattering by dust grains, thus complicating the search for magnetic fields in these sources. While on one hand all of these results challenge our understanding of both magnetic grain-alignment and grain growth, they also have the potential to open up new windows into the dust-grain properties and radiation environments in young star-forming sources.