Resolved Dust in z ≈ 1 Galaxies with JWST/MIRI MRS: Survey Description and First View on Polycyclic Aromatic Hydrocarbons, Mid-infrared Atomic Emission, and Warm H2

Abstract

Dust is a key component of galaxies that regulates their thermal balance and, consequently, star formation and the buildup of stellar mass. Polycyclic aromatic hydrocarbons (PAHs) are responsible for reprocessing the radiative energy of galaxies, thus tracing dust evolution. Using JWST/MIRI Medium Resolution Spectroscopy (MRS), we present the first resolved view of the PAHs and mid-infrared emission lines in a sample of eight z ≈ 1 galaxies. A key novelty is our ability to directly map PAH emission near the end of cosmic noon at JWST’s limits. The sample is selected to be on the star-forming main sequence with stellar masses M⋆ = 1010.6−11.2 M⊙ and infrared luminosities LIR = 1011.5−11.9 L⊙. Two of them contain active galactic nuclei (AGN), and two are interacting systems. We detect and quantify primary PAH emissions from 3.3 to 11.3 μm throughout the galaxies, alongside atomic fine-structure lines (Ar, Ne, and Fe), Brα, and H2 rotational transitions. Through PAH ratio diagnostics and comparison to theoretical models, we qualitatively probe the physical properties of PAH molecules, i.e., size and charge. The AGN and mergers in our sample exhibit a higher fraction of neutral PAHs, possibly related to high radiation intensity and/or shocks, as suggested by increased atomic and H2 line ratios. Leveraging the integral field units data, we find that the grain sizes of the centrally located PAHs tend to be larger and less ionized than those in the outskirts of the galaxies. Finally, we compare our results to observations of PAHs in local and similar-redshift galaxies, revealing a potential evolutionary trend when controlling LIR.