A study of polycyclic aromatic nitrogen heterocycles (PANHs) in starburst-dominated galaxies: variations in the 6.2 ${\mu}$m emission profile

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, 206 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 the breakdown of 169 sources into the Peeter's A, B and C classes (Peeters et al. 2002). 73.4% of these galaxies were classified as class A, 24.8% were as class B and 1.8% 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.