Spitzer characterisation of dust in an anomalous emission region: the
  Perseus cloud
  Anomalous microwave emission is known to exist in the Perseus cloud. One of
the most promising candidates to explain this excess of emission is electric
dipole radiation from rapidly rotating very small dust grains, commonly
referred to as spinning dust. Photometric data obtained with the Spitzer Space
Telescope have been reprocessed and used in conjunction with the dust emission
model DUSTEM to characterise the properties of the dust within the cloud. This
analysis has allowed us to constrain spatial variations in the strength of the
interstellar radiation field ($\chi_\mathrm{ISRF}$), the mass abundances of the
PAHs and VSGs relative to the BGs (Y$_\mathrm{PAH}$ and Y$_\mathrm{VSG}$), the
column density of hydrogen (N$_\mathrm{H}$) and the equilibrium dust
temperature (T$_\mathrm{dust}$). The parameter maps of Y$_\mathrm{PAH}$,
Y$_\mathrm{VSG}$ and $\chi_\mathrm{ISRF}$ are the first of their kind to be
produced for the Perseus cloud, and we used these maps to investigate the
physical conditions in which anomalous emission is observed. We find that in
regions of anomalous emission the strength of the ISRF, and consequently the
equilibrium temperature of the dust, is enhanced while there is no significant
variation in the abundances of the PAHs and the VSGs or the column density of
hydrogen. We interpret these results as an indication that the enhancement in
$\chi_\mathrm{ISRF}$ might be affecting the properties of the small
stochastically heated dust grains resulting in an increase in the spinning dust
emission observed at 33 GHz. This is the first time that such an investigation
has been performed, and we believe that this type of analysis creates a new
perspective in the field of anomalous emission studies, and represents a
powerful new tool for constraining spinning dust models.
