Variations in the 6.2 $\mu$m polycyclic aromatic hydrocarbon band in Active Galactic Nuclei- and Starburst-dominated galaxies

TL;DR

This study examines the variations of the 6.2 μm PAH emission feature in a diverse sample of galaxies, revealing predominant class A profiles and the influence of secondary spectral features on PAH classification.

Contribution

It provides a detailed analysis of PAH profile variations across different galaxy types and introduces the impact of secondary features on spectral classification.

Findings

80% of galaxies show class A PAH profiles

Water ice absorption has minimal effect on PAH bands

Secondary spectral features influence PAH profile classification

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are fundamental to understanding the interstellar medium (ISM) of several astrophysical objects. Normally present in Starburst (SB) galaxies, they have also been more frequently detected in active galaxy nuclei (AGNs), suggesting an inner dusty torus that can shield the radiation from the central black role. In this work, we analyze the 6.2 $\mu$m PAH band of SB-, AGN- and mixed-dominated spectra from 175 IDEOS database galaxies. After fitting of the band, the sources were distributed into the Peeters' A, B and C classes according to their profile peak positions. Class A objects are predominant in 80% of the entire sample, which could indicate the presence of PAHs with nitrogen incorporation. The water ice absorption at 6.0 $\mu$m was also studied in eleven objects, and it affected the PAH band poorly. A prominent second spectral feature after 6.3 $\mu$m is present in ten galaxies. Fitting both PAH profiles at 6.2 $\mu$m changes all the fit results: the first profile is consistently blue-shifted and classified as class A due to the presence of the second component. Further studies are needed to better comprehend these PAH trends in galactic environments.