GTC/CanariCam mid-IR imaging of the fullerene-rich Planetary Nebula IC
  418: searching for the spatial distribution of fullerene-like molecules
  We present seeing-limited narrow-band mid-IR GTC/CanariCam images of the
spatially extended fullerene-containing planetary nebula (PN) IC 418. The
narrow-band images cover the C60 fullerene band at 17.4 {\mu}m, the polycyclic
aromatic hydrocarbon like (PAH-like) feature at 11.3 {\mu}m, the broad 9-13
{\mu}m feature, and their adjacent continua at 9.8 and 20.5 {\mu}m. We study
the relative spatial distribution of these complex species, all detected in the
Spitzer and Infrared Space Observatory (ISO) spectra of IC 418, with the aim of
getting observational constraints to the formation process of fullerenes in
H-rich circumstellar environments. A similar ring-like extended structure is
seen in all narrow-band filters, except in the dust continuum emission at 9.8
{\mu}m, which peaks closer to the central star. The continuum-subtracted images
display a clear ring-like extended structure for the carrier of the broad 9-13
{\mu}m emission, while the spatial distribution of the (PAH-like) 11.3 {\mu}m
emission is not so well defined. Interestingly, a residual C60 17.4 {\mu}m
emission (at about 4-{\sigma} from the sky background) is seen when subtracting
the dust continuum emission at 20.5 {\mu}m. This residual C60 emission, if
real, might have several interpretations; the most exciting being perhaps that
other fullerene-based species like hydrogenated fullerenes with very low
H-content may contribute to the observed 17.4 {\mu}m emission. We conclude that
higher sensitivity mid-IR images and spatially resolved spectroscopic
observations (especially in the Q-band) are necessary to get some clues about
fullerene formation in PNe.
