G C JonesM BétherminY FudamotoM GinolfiP CapakP CassataA FaisstO Le FèvreD SchaererJ D SilvermanLin YanS BardelliM BoquienA CimattiM Dessauges-ZavadskyM GiavaliscoC GruppioniIbar, EduardoEduardoIbarY KhusanovaA M KoekemoerB C LemauxF LoiaconoR MaiolinoP A OeschF PozziD RiechersG RodighieroM TaliaL ValliniD VerganiG ZamoraniE Zucca2025-04-152025-04-152020-01-0110.1093/mnrasl/slz1542-s2.0-85076555546https://cris-uv-2.scimago.es/handle/123456789/2438WOS:000525753500005We report the detection of [C II] λ158 μm emission from a system of three closely separated sources in the Cosmic Evolution Survey (COSMOS) field at z ∼ 4.56, as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Large Program to INvestigate C II at Early times (ALPINE). The two most luminous sources are closely associated, both spatially (1.6 arcsec ∼ 11 kpc) and in velocity (∼100 km s−1), while the third source is slightly more distant (2.8 arcsec ∼ 18 kpc, ∼300 km s−1). The second most luminous source features a slight velocity gradient, while no significant velocity gradient is seen in the other two sources. Using the observed [C II] luminosities, we derive a total log10(SFR[C II] [M☉ yr−1]) = 2.8 ± 0.2, which may be split into contributions of 59, 31, and 10 per cent from the central, east, and west sources, respectively. Comparison of these [C II] detections to recent zoom-in cosmological simulations suggests an ongoing major merger. We are thus witnessing a system in a major phase of mass build-up by merging, including an ongoing major merger and an upcoming minor merger, which is expected to end up in a single massive galaxy by z ∼ 2.5.enacceso abiertoAstronomy And AstrophysicsSpace And Planetary Sciencereview