The ALPINE-ALMA [C II] survey: a triple merger at z ∼ 4.56
Cimatti, A.; Maiolino, R.; Pozzi, F.; Rodighiero, G.; Schaerer, D.; Béthermin, M.; Giavalisco, M.; Silverman, J. D.; Boquien, M.; Ibar, E.; Ginolfi, M.; Oesch, P. A.; Capak, P.; Dessauges-Zavadsky, M.; Koekemoer, A. M.; Gruppioni, C.; Fudamoto, Y.; Riechers, D.; Zamorani, G.; Le Fèvre, O.; Bardelli, S.; Zucca, E.; Talia, M.; Cassata, P.; Vallini, L.; Lemaux, B. C.; Faisst, A.; Vergani, D.; Yan, Lin; Jones, G. C.; Loiacono, F.; Khusanova, Y.
United Kingdom, France, Switzerland, United States, Italy, Japan, Chile, Denmark, Germany, Netherlands
Abstract
We 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 log_{10}(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.