Spinning dust emission from circumstellar disks and its role in excess
  microwave emission
  Electric dipole emission from rapidly spinning polycyclic aromatic
hydrocarbons (PAHs) is widely believed as an origin of anomalous microwave
emission (AME), but recently it encounters a setback due to the non-correlation
of AME with PAH abundance seen in a full-sky analysis. Microwave observations
for specific regions with well-constrained PAH features would be crucial to
test the spinning dust hypothesis. In this paper, we present physical modeling
of microwave emission from spinning PAHs from protoplanetary disks (PPDs)
around Herbig Ae/Be stars and T-Tauri stars where PAH features are well
observed. Guided by the presence of 10 $\mu$m silicate features in some PPDs,
we also model microwave emission from spinning nanosilicates. Thermal emission
from big dust grains is computed using the Monte Carlo radiative transfer code.
Our numerical results demonstrate that microwave emission from either spinning
PAHs or spinning nanosilicates dominates over thermal dust at frequencies $\nu<
60$ GHz, even in the presence of significant grain growth. Finally, we attempt
to fit mm-cm observational data with both thermal dust and spinning dust for
several disks around Herbig Ae/Be stars that exhibit PAH features and find that
spinning dust can successfully reproduce the observed excess microwave emission
(EME). Future radio observations with ngVLA, SKA and ALMA Band 1 would be
valuable for elucidating the origin of EME and potentially open a new window
for probing nanoparticles in circumstellar disks.
