Characterizing magnetic field morphologies in three Serpens protostellar
  cores with ALMA
  With the aim of characterizing the dynamical processes involved in the
formation of young protostars, we present high angular resolution ALMA dust
polarization observations of the Class 0 protostellar cores Serpens SMM1, Emb
8(N), and Emb 8. With spatial resolutions ranging from 150 to 40 au at 870
{\mu}m, we find unexpectedly high values of the polarization fraction along the
outflow cavity walls in Serpens Emb8(N). We use 3 mm and 1 mm molecular tracers
to investigate outflow and dense gas properties and their correlation with the
polarization. These observations allow us to investigate the physical processes
involved in the Radiative Alignment Torques (RATs) acting on dust grains along
the outflow cavity walls, which experience irradiation from accretion processes
and outflow shocks. The inner core of SMM1-a presents a polarization pattern
with a poloidal magnetic field at the bases of the two lobes of the bipolar
outflow. To the south of SMM1-a we see two polarized filaments, one of which
seems to trace the redshifted outflow cavity wall. The other may be an
accretion streamer of material infalling onto the central protostar. We propose
that the polarized emission we see at millimeter wavelengths along the
irradiated cavity walls can be reconciled with the expectations of RAT theory
if the aligned grains present at '<' 500 au scales in Class 0 envelopes have
grown larger than the 0.1 {\mu}m size of ISM dust grains. Our observations
allow us to constrain the star-forming sources magnetic field morphologies
within the central cores, along the outflow cavity walls, and in possible
accretion streamers.
