Carbon envelopes around merging galaxies at z ~ 4.5

Abstract: Galaxies evolve through a dynamic exchange of material with their immediate surrounding environment, the so-called circumgalactic medium (CGM). Understanding the physics of gas flows and the nature of the CGM is thus fundamental to studying galaxy evolution, especially at $4 \leq z \leq 6$ (i.e. at post-Reionization Epoch) when galaxies rapidly assembled their masses and reached their chemical maturity. Galactic outflows are predicted to enrich the CGM with metals, although gas stripping in systems undergoing 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 $z \sim 4.5$, observed by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE). To do so, we study the nature of the [CII]158 $\mu$m emission in the CGM around these systems, using simulations to help disentangle the mechanisms contributing to the CGM metal pollution. By adopting an updated classification of major merger systems in the ALPINE survey, we select and analyze merging galaxies whose components can be spatially and/or spectrally resolved in a robust way. Thus, we can distinguish between the [CII] emission coming from the single components of the system and that coming from the system as a whole. We also make use of the \texttt{dustyGadget} cosmological simulation to select synthetic analogs of observed galaxies and guide the interpretation of the observational results. We find a large diffuse [CII] envelope ($\gtrsim 20 $ kpc) embedding all the merging systems, with at least $25 \%$ of the total [CII] emission coming from the medium \textit{between} the galaxies. Using predictions from \texttt{dustyGadget} we suggest that this emission has a multi-fold nature, with dynamical interactions between galaxies playing a major role in stripping the gas and enriching the medium with heavy elements.}