PAH features within few hundred parsecs of active galactic nuclei
  Spectral features from PAH molecules observed in the mid-IR range are
typically used to infer the amount of recent and ongoing star formation (SF) on
kpc scales around AGN where more traditional methods fail. This assumes that
the observed PAH features are excited predominantly by SF. With current
ground-based telescopes and the upcoming JWST, much smaller spatial scales can
be probed and we aim at testing this assumption in the range of few tens to few
hundreds of pc. For that, we spatially map the emitted 11.3{\mu}m PAH surface
flux as a function of distance from 0.4-4 arcsec from the centre in 28 nearby
AGN using ground-based high-angular resolution mid-IR spectroscopy. We detect
and extract the 11.3{\mu}m PAH feature in 13 AGN. The fluxes within each
aperture are scaled to a luminosity-normalised distance from the nucleus to be
able to compare intrinsic spatial scales of AGN radiation spanning about 2
orders of magnitude in luminosity. For this, we establish an empirical relation
between the absorption-corrected X-ray luminosity and the sublimation radius in
these sources. Once normalised, the radial profiles of the emitted PAH surface
flux show similar radial slopes, with a power-law index of approximately -1.1,
and similar absolute values, consistent within a factor of a few of each other
as expected from the uncertainty in the intrinsic scale estimate. We interpret
this as evidence that the profiles are caused by a common compact central
physical process, either the AGN itself or circumnuclear SF linked in strength
to the AGN power. A photoionisation-based model of an AGN exciting dense clouds
in its environment can reproduce the observed radial slope and confirms that
the AGN radiation field is strong enough to explain the observed PAH surface
fluxes within ~10-500 pc of the nucleus. Our results advice caution in the use
of PAH emission as a SF tracer within a kpc around AGN.
