We present ALMA observations of a merging system at z \sim 4.57 , observed as a part of the ALMA Large Program to INvestigate [ CII ] at Early times ( ALPINE ) survey .
Combining ALMA [ CII ] 158 \mu m and far-infrared continuum data with multi-wavelength ancillary data we find that the system is composed of two massive ( M _ { \star } \gtrsim 10 ^ { 10 } ~ { } { M _ { \odot } } ) star-forming galaxies experiencing a major merger ( stellar mass ratio r _ { mass } \gtrsim 0.9 ) at close spatial ( \sim 13 kpc ; projected ) and velocity ( \Delta v < 300 ~ { } { km~ { } s ^ { -1 } } ) separations , and two additional faint narrow [ CII ] -emitting satellites .
The overall system belongs to a larger-scale protocluster environment and is coincident to one of its overdensity peaks .
ALMA reveals also the presence of [ CII ] emission arising from a circumgalactic gas structure , extending out to \sim 30 kpc .
Our morpho-spectral decomposition analysis shows that about 50 \% of the total flux resides between the individual galaxy components , in a metal-enriched gaseous envelope characterized by a disturbed morphology and complex kinematics .
Similarly to observations of shock-excited [ CII ] emitted from tidal tails in local groups , our results can be interpreted as a possible signature of interstellar gas stripped by strong gravitational interactions , with a possible contribution from material ejected by galactic outflows and emission triggered by star formation in small faint satellites .
Our findings suggest that mergers could be an efficient mechanism of gas mixing in the circumgalactic medium around high- z galaxies , and thus play a key role in the galaxy baryon cycle at early epochs .