Spinning dust emission from ultrasmall silicates: emissivity and
  polarization spectrum
  Anomalous microwave emission (AME) is an important Galactic foreground of
Cosmic Microwave Background (CMB) radiation. It is believed that the AME arises
from rotational emission by spinning polycyclic aromatic hydrocarbons (PAHs) in
the interstellar medium (ISM). In this paper, we assume that a population of
ultrasmall silicate grains may exist in the ISM, and quantify rotational
emissivity from these tiny particles and its polarization spectrum. We found
that spinning silicate nanoparticles can produce strong rotational emission
when those small grains follow a log-normal size distribution. The polarization
fraction of spinning dust emission from tiny silicates increases with
decreasing the dipole moment per atom ($\beta$) and can reach $P\sim 20\%$ for
$\beta\sim 0.1$D at grain temperature of 60 K. We identify a parameter space
$(\beta,Y_{Si})$ for silicate nanoparticles in which its rotational emission
can adequately reproduce both the observed AME and the polarization of the AME,
without violating the observational constraints by the ultraviolet extinction
and polarization of starlight. Our results reveal that rotational emission from
spinning silicate may be an important source of the AME.
