In a groundbreaking study, a team of researchers led by Elizabeth J. Tarantino from the University of Virginia has utilized the James Webb Space Telescope (JWST) to observe the growth of aromatic hydrocarbon dust particles in the extremely metal-poor galaxy Sextans A. The team includes scientists from various institutions such as the Space Telescope Science Institute, the University of Western Ontario, and the University of Arizona.
The mid-infrared spectrum of star-forming galaxies with high metallicity is typically dominated by emission features from small carbonaceous dust grains, known as polycyclic aromatic hydrocarbons (PAHs). However, in metal-poor galaxies, the abundance of PAHs relative to the total dust sharply declines, and the reason for this deficit has remained unknown. The researchers present JWST observations that detect and resolve emission from PAHs in Sextans A, which has a metallicity of only 7% of the Sun’s. This marks the lowest metallicity detection of PAH emission to date.
In contrast to higher metallicity galaxies, the clumps of PAH emission in Sextans A are compact, ranging from 0.5 to 1.5 arcseconds, or 3 to 10 parsecs in size. This compactness explains why PAH emission had previously evaded detection by lower resolution instruments like Spitzer. The ratios between the 3.3, 7.7, and 11.3 micrometer PAH features indicate that the PAH grains in Sextans A are small and neutral, with no evidence of significant processing from the hard radiation fields within the galaxy.
These findings suggest that the low PAH abundance in Sextans A is likely due to inhibited grain growth rather than enhanced destruction. The compact clumps of PAH emission are likely active sites of in-situ PAH growth within a dense, well-shielded phase of the interstellar medium. The research demonstrates that PAHs can form and survive in extremely metal-poor environments, which were common early in the evolution of the Universe.
The practical applications for the energy sector lie in understanding the formation and behavior of PAHs in various environments. PAHs are significant components of soot and other combustion byproducts, and their behavior can impact the efficiency and environmental impact of energy production processes. By studying the formation and growth of PAHs in extreme environments, researchers can gain insights into optimizing combustion processes and reducing emissions in the energy industry.
This research was published in the journal Nature Astronomy.
This article is based on research available at arXiv.