Carbon envelopes around merging galaxies at z ~ 4.5

Galaxies evolve through a dynamic exchange of material with their immediatesurrounding environment, the circumgalactic medium (CGM). Understanding thephysics of gas flows and the nature of the CGM is thus fundamental to studyinggalaxy evolution, especially at $4 \leq z \leq 6$ when galaxies rapidlyassembled their masses and reached their chemical maturity. Galactic outflowsare predicted to enrich the CGM with metals, although gas stripping in systemsundergoing a major merger has also been suggested to play a role. In this work,we explore the metal enrichment of the medium around merging galaxies at$z\sim4.5$, observed by the ALMA Large Program to INvestigate [CII] at Earlytimes (ALPINE) survey. To do so, we study the nature of the [CII]158 $\mu$memission in the CGM around these systems, using simulations to help disentanglethe mechanisms contributing to the CGM metal pollution. By adopting an updatedclassification of major merger systems in the ALPINE survey, we select andanalyse merging galaxies whose components can be spatially and/or spectrallyresolved in a robust way. In this way, we can distinguish between the [CII]emission coming from the single components of the system and that coming fromthe system as a whole. We also make use of the dustyGadget cosmologicalsimulation to select synthetic analogues of observed galaxies and guide theinterpretation of the observational results. We find a large diffuse [CII]envelope (> 20 kpc) embedding all the merging systems, with around 50% of thetotal [CII] emission coming from the medium between the galaxies. Usingpredictions from dustyGadget we suggest that this emission has a two-foldnature: it is due to both dynamical interactions between the galaxies whichresult in tidal stripped gas and the presence of star-forming satellites(currently unresolved by ALMA) that enrich the medium with heavy elements.