Hydrocarbon dust, the main component of interstellar dust, consists mainly of polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons. This dust is assumed to be affected by interstellar radiation and shock waves, but the detailed mechanisms are not fully understood so far.

The study included a comprehensive analysis conducted by the Japanese astronomy community, with scientists examining the relationship between the brightness emitted by hydrocarbon dust and the total infrared brightness (LIR) of 138 galaxies.

Using near-infrared data (2.5-5 μm) from the AKARI space telescope, they measured the brightness of aromatic hydrocarbons with a wavelength of 3.3 μm (Laromatic) and aliphatic hydrocarbons with a wavelength of 3.4-3.6 μm (Laliphatic).

Additionally, the team used photometry data from the AKARI, WISE, and IRAS telescopes to create models of the spectral energy distribution of these galaxies, which allowed them to estimate the galaxies’ total infrared brightness and emission field density.

Research results

The results show that galaxies with higher infrared luminosity have lower luminosity ratios of aliphatic and aromatic components, and an anti-correlation is observed between this ratio and the intensity of the radiation field.

It is noteworthy that these low values ​​are found mainly in galaxies in the merger stage, indicating that in such environments the aliphatic components decay faster than the aromatic ones.

As a result, scientists concluded that hydrocarbon dust likely underwent dissociation under the influence of shock waves and radiation during the merger of galaxies. The luminosity ratio of aliphatic to aromatic components decreases in extreme interstellar conditions because aliphatic components are chemically weaker than their aromatic counterparts.