Peeling Back the Layers of Extinction of Dusty Galaxies in the Era of JWST: Modelling Joint NIRSpec + MIRI Spectra at rest-frame 1.5-28 $\mu$m

Abstract

We present an analysis of the combined NIRSpec and MIRI spectra of dusty galaxies between 1.5 - 28 $\mu$m restframe by implementing a differential extinction model, where the strength of extinction varies across the spectrum as different layers of the obscuring dust are probed. Our model is able to recover a 2D distribution of dust temperature and extinction which allows inference of the physical nature of the dust in these environments. We show that differential extinction is necessary to reproduce the spectra of 4 highly obscured Luminous Infrared Galaxies observed with NIRSpec IFU and MIRI MRS, where simple screen or uniformly mixed dust distributions fail to fit the data. We additionally compare the extinction of HII regions in these galaxies via hydrogen recombination lines, the extinction of molecular gas via the H$_2$ lines, Polycyclic Aromatic Hydrocarbons via the 12.7/11.3 PAH ratio and the stellar continuum. We find that the molecular gas is deeply buried with the HII regions in star-forming regions, with a similar extinction to the hottest dust components. However we find the cooler dust to be less obscured, at a similar extinction to the stellar continuum and PAHs. The nuclei show a complex dust distribution with VV114 NE, NGC 3256 S, IIZw96 SW showing a deeply buried continuum source relative to the molecular gas/HII regions. Additionally, NGC 3256 S, NGC 7469 and VV114 SW show an isolated hot dust component, indicative of AGN heating, where NGC 3256 S and NGC 7469 are previously known AGN.