Galaxies continuously reprocess their interstellar material. We can therefore expect changing dust grain properties in galaxies that have followed different evolutionary pathways. Determining the intrinsic dust grain mix of a galaxy helps in reconstructing its evolutionary history. Early-type galaxies occasionally display regular dust lanes in their central regions. Owing to the relatively simple geometry and composition of their stellar bodies, these galaxies are ideal to disentangle dust mix variations from geometric effects. We therefore modelled the various components of such a galaxy (FCC 167). We reconstructed its recent history and investigated the possible fate of the dust lane. Observations from MUSE and the Atacama Large Millimeter/submillimeter Array (ALMA) reveal a nested interstellar medium structure. An ionised-gas disc pervades the central regions of FCC 167, including those occupied by the main dust lane. Inward of the dust lane, we also find a disc/ring of cold molecular gas where stars are forming and HII regions contribute to the ionised-gas emission. Further in, the gas ionisation points towards an active galactic nucleus and the fuelling of a central supermassive black hole from its surrounding ionised and molecular reservoir. Observational constraints and radiative transfer models suggest the dust and gas are distributed in a ring-like geometry and the dust mix lacks small grains. The derived dust destruction timescales from sputtering in hot gas are short, and we conclude that the dust must be strongly self-shielding and clumpy or will quickly be eroded and disappear. Our findings show how detailed analyses of individual systems can complement statistical studies of dust-lane ETGs.
Unusual Galactic H ii Regions at the Intersection of the Central Molecular Zone and the Far Dust Lane
