Uncovering the multi-scale structure of dust distribution in nearby galaxies

TL;DR

This study uses advanced image decomposition to analyze dust emission in nearby galaxies, revealing scale-dependent properties of PAH molecules and the interstellar medium with high-resolution JWST data.

Contribution

We enhance the constrained diffusion decomposition algorithm to distinguish emission sources at multiple scales, providing new insights into dust and PAH behavior in galaxies.

Findings

PAH emission transitions around 300 pc with weaker PAH fraction at smaller scales

Smaller PAH fractions observed in bright, star-forming environments

A transition from power-law to log-normal PDFs occurs around 200 pc in ISM structures

Abstract

High-resolution JWST-MIRI images now allow us to resolve in great detail the multi-scale nature of the emission in nearby star-forming galaxies, from compact star-forming regions to large-scale diffuse emission, giving new insights into dust emission, its composition, and the surrounding interstellar medium (ISM). We aim to understand at which scale the different processes driving dust emission in mid-infrared (7.7-21 um) wavelengths take place and if we can disentangle dense regions' emission from emission linked to a more diffuse component. We use and enhance the constrained diffusion decomposition (CDD) algorithm, an alternative to the wavelet transform decomposition, to disentangle the emission coming from compact regions from the emission originating from diffuse sources. This allows us to cleanly quantify the mid-IR spectral properties of the ISM at intervals within a continuum of physical scales. We find a transition scale of PAH emission around 300 pc, with weaker PAH fraction at smaller scales, highlighting the destruction of PAHs in HII regions. We also show variations in the PAH fraction in different morphological environments, with a smaller fraction in bright and star-forming environments. Studying and comparing the probability distribution functions (PDFs) of HII regions and diffuse ISM with the PDFs at different scales, we find a similar separation scale around 200 pc at which we observe a transition from a power-law PDF for dense structures to a log-normal one for the diffuse ISM.