Variations in the 6.2 $\mu$m emission profile in starburst-dominated
  galaxies: a signature of polycyclic aromatic nitrogen heterocycles (PANHs)?
  Analyses of the polycyclic aromatic hydrocarbon (PAH) feature profiles,
especially the 6.2 $\mu$m feature, could indicate the presence of nitrogen
incorporated in their aromatic rings. In this work, 155 predominantly
starburst-dominated galaxies (including HII regions and Seyferts, for example),
extracted from the Spitzer/IRS ATLAS project (Hern\'an-Caballero &
Hatziminaoglou 2011), have their 6.2 $\mu$m profiles fitted allowing their
separation into the Peeters' A, B and C classes (Peeters et al. 2002). 67% of
these galaxies were classified as class A, 31% were as class B and 2% as class
C. Currently class A sources, corresponding to a central wavelength near 6.22
$\mu$m, seem only to be explained by polycyclic aromatic nitrogen heterocycles
(PANH, Hudgins et al. 2005), whereas class B may represent a mix between PAHs
and PANHs emissions or different PANH structures or ionization states.
Therefore, these spectra suggest a significant presence of PANHs in the
interstellar medium (ISM) of these galaxies that could be related to their
starburst-dominated emission. These results also suggest that PANHs constitute
another reservoir of nitrogen in the Universe, in addition to the nitrogen in
the gas phase and ices of the ISM.
