A new census of dust and polycyclic aromatic hydrocarbons at z=0.7-2 with JWST MIRI

This paper utilises the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) to extend the observational studies of dust and polycyclic aromatic hydrocarbon (PAH) emission to a new mass and star formation rate (SFR) parameter space beyond our local Universe. The combination of fully sampled spectral energy distributions (SEDs) with multiple mid-infrared (mid-IR) bands and the unprecedented sensitivity of MIRI allows us to investigate dust obscuration and PAH behaviour from $z=0.7$ up to $z=2$ in typical main-sequence galaxies. Our focus is on constraining the evolution of PAH strength and the dust-obscured luminosity fraction before and during cosmic noon, the epoch of peak star formation activity in the Universe. um um um um imaging data, enhancing our understanding of the physical characteristics of dust within these galaxies. We find a strong correlation between the fraction of dust in PAHs (PAH fraction qpah ) with stellar mass. Moreover the sub-sample with robust qpah measurements ($N=216$) shows a similar behaviour between qpah and gas-phase metallicity to that at $z suggesting a universal relation: qpah is constant ($ 3.4$) above a metallicity of $Z odot $ and decreases to $<1$ at metallicities $ odot $. This indicates that metallicity is a good indicator of the interstellar medium properties that affect the balance between the formation and destruction of PAHs. The lack of a redshift evolution from $z 0-2$ also implies that above $Z odot $ the PAH emission effectively traces obscured luminosity and the previous locally calibrated PAH-SFR calibrations remain applicable in this metallicity regime. We observe a strong correlation between the obscured UV luminosity fraction (ratio of obscured to total luminosity) and stellar mass. Above the stellar mass of $M_*>5 Msun on average, more than half of the emitted luminosity is obscured, while there exists a non-negligible population of lower-mass galaxies with $>50$ obscured fractions. At a fixed mass, the obscured fraction correlates with SFR surface density. This is a result of higher dust covering fractions in galaxies with more compact star-forming regions. Similarly, galaxies with high IRX (IR to UV luminosity) at a given mass or UV continuum slope (beta ) tend to have higher Ssfr and shallower attenuation curves, owing to their higher effective dust optical depths and more compact star-forming regions.