Profile comparison of the 6-9 $\mu$m polycyclic aromatic hydrocarbon
  bands in starburst-dominated galaxies
  Polycyclic aromatic hydrocarbons (PAHs) are of great astrochemical and
astrobiological interest due to their potential to form prebiotic molecules. We
analyse the 7.7 and 8.6 ${\mu}$m PAH bands in 126 predominantly
starburst-dominated galaxies extracted from the Spitzer/IRS ATLAS project.
Based on the peak positions of these bands, we classify them into the different
A, B, and C Peeters' classes, which allows us to address the potential
characteristics of the PAH emitting population. We compare this analysis with
previous work focused on the 6.2 ${\mu}$m PAH band for the same sample. For the
first time in the literature, this statistical analysis is performed on a
sample of galaxies. In our sample, the 7.7 ${\mu}$m complex is equally
distributed in A and B object's class while the 8.6 ${\mu}$m band presents more
B class sources. Moreover, 39 per cent of the galaxies were distributed into A
class objects for both 6.2 and 7.7 ${\mu}$m bands and only 18 per cent received
the same A classification for the three bands. The "A A A" galaxies presented
higher temperatures and less dust in their interstellar medium. Considering the
redshift range covered by our sample, the distribution of the three bands into
the different Peeters' classes reveals a potential cosmological evolution in
the molecular nature of the PAHs that dominate the interstellar medium in these
galaxies, where B class objects seem to be more frequent at higher redshifts
and, therefore, further studies have to be addressed.
